Idle Problem

[westonben]

Hi, I'm having some problems with my Series 1 Disco. It's a gulf spec 1999 3.9i without Cat. It's covered 104k kms.

Symptoms: When the engine is hot, pulling up at lights etc. the revs can dip. However, when stationary the idle also bounces up and down a little. It sits steady at about 700rpm for a while before dropping bit at a time down to 500rpm (engine sounds like it's stalling/labouring) a little click can be heard and the revs jump back up to 700rpm. Cycle repeats until I'm rolling again. No other issues with running.

What is ruled out:

MAF (tried known working ones)
TPS (tried known working ones)
AICV/Stepper (replaced) Mating surfaces spottlessly cleaned.
Checked leaks on all pipework
Fuel Pump (new)
Fuel Filter (new)
Leads/Plugs/Rotor Arm/Dizzy Cap (new)
Coolant Temp Sensor (new)
Throttle body (cleaned spotlessly)
Crankcase Inlet Air Filter (cleaned)

What's left:
Fuel Pressure Regulator
Fuel temperature sensor
Blocked injectors (tried cleaners)
Head Gasket
VSS
ECU
Slit Wrists?

Where do I go from here? The dealer has not been able to diagnose the problem and the other garages here (qatar) are very crude.

Appreciate any help as it's getting well beyond a joke now!

Thanks

Ben

[Utemad]

The Idle Air Control valve at the back of the plenum chamber.

Pull it out and clean up the plunger and its mating surface.
Maybe need to replace it?

Mine used to do what you describe but not quite as bad. Usually only when it was cold.

[INter674]

. that sounds normal to me - ours has always done that. Young relative actually asked me why does it do that...to which I replied...it's a Land Rover, that's why....and he nodded sagely...

[Utemad]

Just saw the IAC valve is on your list of done things.

If you unplug it does the problem stop or at least change?

[westonben]

It might normal to fluctuate a bit, but it's also occasionally stalling. That can't be normal?

WRT to pulling the stepper, do I do this while the engine is running????

[mike 90 RR]

If you have no catalic converter // then you did a exhaust change?? .. Did you keep or are you running the Oxy sensors??

[Utemad]

WRT to pulling the stepper, do I do this while the engine is running????

I just meant unplug it.

When the engine is running unplug it and see if the idle stays the same or continues to fluctuate.

[mickashay]

mine is doing this also,when i pull up the revs bounce up and down then are ok when driving,was out in some very slippery hills today and it was doing it real bad when coming down the hills and stalling alot,i have cleaned the idle air control but still didnt change any thing???what else should i look at also

[harry]

If you have no catalic converter // then you did a exhaust change?? .. Did you keep or are you running the Oxy sensors??
i run a 95 aussie disco, factory no o2 sensors or cats, so i guess his is also standard there.
you mention the stepper motor has been cleaned, has it also been lubed in its own shaft?
i also have endured this hunting at the lights and stalling , one fix was the replacement of the engine temp probe, and this problem still persists with mine now and again.
sometimes it is as simple as turning the ign off, waiting briefly and re starting the engine
i really believe the problem is directly related to the temp sensor.
however someone may be able to give you more clues - good hunting [no pun intended]

[duncanw]

the exact same thing happened to mine, I cleaned out the stepper motor with no change so I bought a new one and it fixed the problem.

Regarding whats remaining on the list of possibles, I doubt very much its the fuel pressure regulator, mine also died and it was crap across the whole rev range, could only manage 80km top speed and it stank of petrol.

Blocked injectors ? your fuel economy would be crap and it would be lacking power on the whole range, pull your plugs out and have a look at them, if their black it's not usally a good sign

Head Gasket, doubtful, again it would be crap across the whole range, do a compression test and see if its in the normal range.

Maybe if you check your vacuum lines ?

Do you hold the brakes at the lights when the engine wants to die ? I had a faulty brake booster and if I put the brakes on at idle it would drop the revs.

[westonben]

Thanks for the replies guys.

The Disco is standard, gulf spec was without cats and o2 sensors.

It stalls when in drive (it's an auto), but the hunting and engine labouring also occur in park though the revs are much higher (800-900rpm).

The stepper motor is a brand new Land Rover part.

Anyone got any experience of adjusting the MAF? I believe a voltage of 0.7V is correct? Anyone tried anything different?

[PhilipA]

Many(all?) 3.9s deteriorate at idle especially under load.
Once the revs fall to 550 or so the stepper will go up one step thus restoring idle speed. If it gets a little fast the stepper will again drop one step, thus the fluctuating idle.
I believe that this is mainly the age and design of the injectors. They are single hole injectors which dribble rather than spray when they are dirty and/or old. This causes an uneven rich mixture.
There are modern 4 hole Bosch injectors available from the USA at a reasonable price .
Bosch Injectors - Alpha Romeo, Fiat & Jaguar Fuel Injectors (http://www.fiveomotorsport.com/Injector_SetsENGLAND.asp)

I have fitted an earlier set and they improved the idle greatly. However the USA spec cars have cats which can compensate for any injector volume variations, so I cannot guarantee that they will be exactly right for your car. I have a Unichip interceptor that also compensates for any mixture differences.
But I think its worth the risk of a slightly incorrect idle which could be tuned out with the MAF anyway.
Regards Philip A

[westonben]

mine is doing this also,when i pull up the revs bounce up and down then are ok when driving,was out in some very slippery hills today and it was doing it real bad when coming down the hills and stalling alot,i have cleaned the idle air control but still didnt change any thing???what else should i look at also

Check some of things that didn't fix my problem above. Easy one's are to clean the MAF and it's electrical connectors (maybe give them a nip to tighten also). If you cleaned the stepper did you also clean it's mating surface?

[4bee]

I don't know if it's critical but the instructions that came with my Idle Air Control valve states that before inserting it, adjust the pintle length.

ie. From the rear of the cone to the gasket mounting face should be adjusted to 28mm (11/8")
If greater than that, INTERNAL DAMAGE to the valve can occur.

To adjust, compress spring & rotate the pintle inwards to achieve this dimension. Oil the plunger rod.


When replacing valve on engine

DO NOT OVERTIGHTEN. 18 NM (13ft/lbs)
The body is thin at the end of the thread & can snap off.

NB Check the fixing screws that hold the plate to the Throttle Body as air leaks here can cause poor idling.

[westonben]

4Bee, I think you might be on to something with the plate. When I removed it there was no gasket in place. I've ordered one and will see if that fixes it! Will update!

WRT to reassembly of the stepper - here are the instructions I found:

Firstly lightly lubricate the threaded area then refit the spring and screw the cone back into the motor, until the keyway just snags on its locating lug in the motor. Now reconnect the stepper into the car, and cycle the ignition on and off. The unit will wind the assembly back in as the ignition goes off. Disconnect and refit to the plenum chamber.

[4bee]

;)I cleaned the faces, checked the faces for true, & applied a thin bead of blue sealant & refitted it. It is still secure.

I don't have that assy. detail. Interesting. Thanks.



ie. From the rear of the cone to the gasket mounting face should be adjusted to 28mm (11/8")
If greater than that, INTERNAL DAMAGE to the valve can occur.UPDATED

NB NB I believe I misread the fine print on the sheet. IT IS TO THE TIP OF THE CONE/PINTLE TO THE GASKET SEALING FACE 28 mm

My apologies if there are a million IACs around Oz that are stuffed up.;)

[Boxer]

This is the thread I've been dreaming of finding. Only drama is that I've tried quite a few things also. Funnily enough though, after a major service I gave it 2 weeks ago it was driving like a new car. Perfect idle etc. Now it's back to being a bag of crud again.

Someone above mentioned the gasket for the IAC. Mine split, so I had to bandage it. Where do you get them from? hoping after market

[westonben]

I've not seen a gasket for the stepper motor itself for sale. The one I was talking about is for the stepper motor mounting plate on the back of the plenum. It cost 50p from Rimmerbros in the UK for a genuine part.

[Boxer]

Oh, mine was loosely sarcastic towards genuine parts prices though. Shouldn't be a prob finding one. I'm just being lazy.

If anything, I'm hoping that going to LPG will fix the problem.

[westonben]

I'm going to try to adjust the MAF to "tune" the problem. I've not heard of many people trying this, but there aren't too many people out there with non-cat disco's to have tried it.

Anyone gone this route? I'm thinking of dropping the base voltage down a fraction to see if it compensates with more fuel???? :o

[Boxer]

I'm keen on doing this too Ben. I've got access to a dyno and A/F meter. Do you have a diagram of the MAF and pin outs?

Of the two adjusters on it, I have no clue which does what.

[Lucus]

I'd be doing the rounds with a can or carby cleaner looking for vacum leaks before i touched the MAF.........;)

[Boxer]

I'd be doing the rounds with a can or carby cleaner looking for vacum leaks before i touched the MAF.........;)

Done that a few times on mine. When I first bought it I even had the plenum top off and found one of the velocity stacks had come loose and was rattling around. Quick dab of araldite fixed that right up.

[westonben]

Boxer, it should only have one adjustment, a hex head bolt that sets a DC output voltage from the sensor that sets the idle carbon monoxide level (or mixture setting).

Use a voltmeter between red and black wire and blue and red wire check the voltage with the ignition on (you'll need to probe the connector somehow - I managed with trailing some wire out of the connections, but you don't want to damage the connector pins), but the engine not running and make a note in case you need to reset it. The screw allows you to set the carbon monoxide base line with these voltages. The setting of the DC voltage has no effect on the overall voltages produced by the air flow meter output for any given air flow so should only affect idle. I can't see a big problem with playing with this and it should be easy to go back to your previous setting.

Turn the adjustment screw clockwise to richen the mixture, and anticlockwise to lean the mixture. Although it will go from 0 volts to over 3.5 volts you should be aiming for something between 1V and 1.5V.

This unit has 4 connections:

Red/black is Ground
Blue/Green is the Air flow signal- should be .2-.7 volts (no air flow). Tick over on the 3.9 is about 1.7 volts
Brown Orange is +12v
Blue/red is the CO trim value.

To be clear - this will only make any difference to cars without Lambda (O2) sensors.

[Boxer]

Thanks Ben. I'm gonna head to a makes shop to stick it on the gas analyser, will also check the fuel pressure. I'm being lazy again by saying this, but any idea what the base and vac pressures should be?

On top of that, I've had 2 specialists tell me that my MAF might be shagged and I'd be up for about $600. If that's the case, then I'm gonna jam a Microtech on it. At least then I can tune it myself.

[westonben]

Don't have the figures here with me, but will post later if no one else has beaten me to it.

A new MAF is expensive but you could try reconditioned ones, second hand ones and reproduction ones. Check Flea-bay. Any of the 5AM or 3AM meters should work. This one should be ok, he'll ship from the US: http://cgi.ebay.com/ebaymotors/93-1993-Jaguar-XJ6-XJS-MAF-Mass-air-flow-Sensor-Lucas_W0QQcmdZViewItemQQ_trksidZp1638Q2em122QQcate goryZ33557QQihZ012QQitemZ220259775491QQrdZ1QQsspag enameZWD2V

To test the air flow sensors output, connect a voltmeter between the red black wire and blue green wire (sensor output). Remove the air filter and blow into the mouth of the air flow meter (into hole that runs around the edge of the air intake). At tick over the voltage is around 1.7 volts. This should jump when you blow!

[4bee]

Re the IACV adjustment post back a bit.

I should point out that the one I fitted is identical in appearance to the OEM Geguine Parts valve except it's plated finish & not black.

I pulled the piston out yesterday to find the pintle adjustment is different but both posts are correct ^ ^ ^.

My replacement valve is an A/Mkt one. "Standard IAC-030" which is labelled for Land Rover as well as Holden Camira JB Made in the USA, & from memory 50% of the LR price & came from "Automotive Service Solutions" Ph1300 30 40

http://www.efi.com.au/pagePartsnavSensors.php


I originally went searching for GM 25527077 or AC - Delco 217-437 & this seems to be the same one including a better price than LR Genuine Parts.

[Boxer]

Seems like my mixtures are looking good now and from what you mentioned in the other thread Ben, it does make sense, yet the car does seem to be running leaner across the board. Yet, I might still try playing a trick on the computer to see if I can get it even leaner. Based on what this says.



Throttle Position Sensor

The Throttle Position Sensor is mounted on the side of the plenum chamber inlet neck and is directly coupled to the throttle valve shaft. The potentiometer is a resistive device supplied with a voltage from the ECU. Movement of the throttle pedal causes the throttle valve to open, thus rotating the wiper arm within the potentiometer which in turn varies the resistance in proportion to the valve position. The ECU lengthens the injector open time when it detects a change in output voltage (rising) from the potentiometer. In addition, the ECU will weaken the mixture when it detects the potentiometer output voltage is decreasing under deceleration and will shorten the length of time the injectors are open. When the throttle is fully open, the ECU will detect the corresponding throttle potentiometer voltage and will apply full load enrichment. This is a fixed percentage and is independent of temperature. Full load enrichment is also achieved by adjusting the length of the injector open time. When the throttle is closed, overrun fuel cut off or idle speed control may be facilitated dependant on other inputs to the ECU. The throttle position sensor is designed to be self-adaptive. (At least in theory, adjustment is neither possible nor necessary. This is one small advantage of the 14CUX system over the 14CU system.)

To troubleshoot the Throttle Position Sensor, first disconnect system power and then disconnect the EFI Cable Harness from the ECU. Using an Ohmmeter, verify that resistance between terminals 3 and 25 is between 4000 and 6000 Ohms. Next, reconnect the EFI Cable Harness to the ECU, and turn the ignition key switch "on". Take voltmeter readings from pin 20 to ground. With the sensor in the throttle-closed position, you should read 0.085 to 0.545 volts. With the sensor in the throttle-open position, you should read 4.2 to 4.9 volts. In between these extremes, turning the throttle position sensor should produce a smooth sweep of voltage readings.

The Throttle Position Sensor on our example system is marked "215SA", "84925A", "Lucas", "Made in UK", and "2499". It has a 3-lead pigtail on it that's about 6" long, and the 3-pin connector on the end of the pigtail is marked "Rists". The three cables to the pigtail are color coded "yellow", "red" and "green" respectively.

I technically should be able to ever so slightly back off the TPS and therefore reduce the injector open times. I guess it all just depends on making sure the TPS is within spec as per above.

[westonben]

Boxer, it does say that adjustment of the TPS is not possible??

However, I've got a spare TPS if you need it. I'm sure we can come to some agreement! ;)

[westonben]

Well it seems to be fixed. The mechanic had a little wiggle with something around the throttle linkage/accelerator cable and it now seems fine. I wonder if he's tightened the accelerator cable?

Anyway, I'm not complaining as the car is much more driveable now.

They have also "fixed" the problem with the transfer box and I can now get it into low gear ratio, but there does seems to be a lot of noise coming through the selector from the road/engine. I guess they broke something or left something out - any ideas??

[4bee]

little wiggle




Is that the Technical term?

[westonben]

Unfortunately, I didn't get to the bottom of the issue due to the language barrier. I think that maybe he tightened the accelerator cable, but presumably that is just holding the engine above the base idle???

Might be better to loosen back off and adjust the idle by the adjuster?

[Boxer]

Boxer, it does say that adjustment of the TPS is not possible??

However, I've got a spare TPS if you need it. I'm sure we can come to some agreement! ;)

Well... it isn't adjustable, but it can be with a little file or drill bit.

So I did that and it didn't make a lick of difference to the tune. So I put it back to std. :cool:

[westonben]

Boxer, now my own problems are sorted I can think about other peoples!

What is your problem? Burning too rich? What have you tried already and what flavour disco have you got?

Ben

[Boxer]

Nah, honestly, everything seems fine on mine now. The Boxer touch with some valuable info off this forum and the internerd got it running sweet. It even idles like a charm!

And if by flavor, you mean model? It's a plated 95, sold 96 V8i Manual. Sounds like a V8 Supercar :)

[4bee]

Something to consider & check.


After playing with this problem for a few years & trying a lot of things, today I fitted a full set of NGK BPR5EY spark plugs.

Somewhere along the line I had fitted NGK BP6ES. This is a colder plug & with no internal resistor. Why, how? I dunno, but I had for some stupid reason. Don't ask 'cos I don't know.:(

The BPR5EY has a resistor, is a tad hotter & has the all singing all dancing Y shaped electrode tip. The original OEM Champion also was a resistor plug.

********** NGK Frequently Asked Questions (http://www.ngksparkplugs.com/techinfo/spark_plugs/faq/faqresistor.asp) ********

Part of my problem has been sooting up & not self-cleaning & with no resistors who can say how that may have played merry hell with the ECU electronics. Consequently, the idle has been haphazard, to say the least.
Tonight, I saw a whole heap of improvement. An idle that can be controlled & the idle responding up when the air cond is switched on. This has always been a bit crap.

Ok, they are clean new plugs, but according to the book of words if they self-clean & reduce ignition "noise" then I may well be in front after all this time.

Was the non - resistor plug playing up with my electrics? I don't know but if you Google "Resistor Spark Plugs" there has been a lot published on this..

I pose this question because it's possible others or previous owners may have inadvertently fitted non - resistor & cooler plugs & may be one of the causes of what seems to be a common problem with the 3.9 V8i & the 14CUX system.

I'm not saying it will fix a particular problem you may be having, but it might just pay to check what plugs you have fitted just in case.

[4bee]

0700 update.

Very cold engine overnight.



Hit key start, rpm immediately jumped to apx. 1500 on the std. onboard tacho.

Within 2 secs had dropped to 1000 rpm.

Sat there at a nice steady idle & the rpm slowly dropped down as the engine warmed.
I would not normally drive this way with a long warmup, but just let it warm a tad & then drive off allowing the Efi controls to take over.

Am I on a winner? Hopefully, as "she" has never idled as well as this from cold in her short teenage life.:D

[Boxer]

I think I've had a good win tune wise too!. I'm just past a third of an 85 litre tank and have just clocked 268km. Normally I'd be just struggling to get to 200 by half tank! And the car is going great. YET!

I'll start a new thread here, but all of this new mileage has been in 4WD... Thanks to a trip to the dyno. If you think you can help, please click here

http://www.aulro.com/afvb/discovery/61089-d1-v8i-transfer-case-gurus-need-your-smarts.html#post791201

[4bee]

As a reference this is a good read.

Scroll down to Idle Air Valve & you can see why we have problems.


http://www.g33.co.uk/fuel_injection.htm

[JMAN]

while checking my Stepper motor this morning, when I turn the accessories on then off, the stepper buzzes. Then I disconnected it from its housing, repeated the ignition on off sequence. I saw NO movement from the pin/spring assembly, but it was definitly buzzing.
Is it broken??

[Utemad]

JMAN as far as I am aware the way the stepper works is that when you switch off the ignition the stepper tries to wind itself out more steps then it can do. This is to ensure that no matter what position it is in when you shut the engine off, the motor will wind itself all the way to the park position.

So since you pulled it out when it was shut down, it was already in the park position. So giving and removing power again without starting the engine will leave it in the park position and then it will try and wind itself back to the park position.
I don't think I've explained it particularly well but I'd say your stepper is fine.

To test it this might work. Start engine and disconnect stepper when idling. Stop engine and remove stepper from engine. Then turn the ignition on then off. The stepper should be seen to operate. I haven't done this but can't see why it wouldn't work.

[JMAN]

I'll give that a shot. cheers!

[Romulus]

Just reading thorugh this thread and it looks as though the problem has been solved.
I did have a similar problem with my '96 3.9l, idle in drive was all over the place, but was OK in neutral or park, so problem was when engine was 'loaded'.
Replacing the stepper motor helped for about a day then it went back to its old tricks.
So I replaced all ignition leads, new dizzy head, rotor and a new set of spark plugs and that did solve my problem.
It now idles in D in the 650 region with a bit of variation which is to be expected.
However, I still have another problem with starting the engine after it has reached operating temp, I have started a new thread on this, so any help would be greatly appreciated, thanks! :)

[mickashay]

just had my stepper changed and got rid of the bouncing idle but now mine seems to idle at about 1500rpm after driving around for a while,its normal when i start up.

[Slurpie]

My Discovery 1 has been stalling on occassion and I hve been unable to find the problem. It only stalls when the engine is warmed up and sometimes the engine hunts from almost no revs to 1500 rpm. I have replaced the fuel pump and air flow meter, but have now been told that the TPS is suspect.
Any ideas? Where can I buy a TPS in South Africa. The LR dealers are very expensive. The numbers on the unit is 215sa and 70408 A.

[PhilipA]

I was helping a guy in Sweden or somewhere to install a14CUX on an old RR on another forum.
He had this irregular idle problem and it turned out ot be the vacuum advance Diaphragm was split giving an air leak.

Before buying a new TPS, you should test it.There are three wires . one is earth , one 5V and one the return to the ECU. I have forgotten the colours buy easy to tell as one is zero volts, one five and the one you want is about 0.4V at no throttle.
Get a multimeter , preferably the now non existent analogue type and slowly move the throttle open, the voltage should smoothly move from 0.4 or whatever to around 4.5 or so. The important part is that voltage does not drop at any time.
A TPS typical fault does not usually involve idle but the move FROM idle, as they usually wear just off idle, ie where you have your fooT on the throttle most of the time. They ar elike a volume control on an old radio
ie a variable resistor.
Regards Philip A

[4bee]

May I suggest you also check the 3 pin plug/fly lead to the TPS hidden under the Throttle Body & give it a good clean.

[Pierre]

Slurpie, buy from UK - Craddock, Paddock, Rimmer, Island.

HTH

Pete