Fast Idle problem-94 Disco V8

[muddy69]

Here's my problem - On cold start, engine runs high idle around 1500rpm for about 10 sec's before returning to normal idle around 700rpm in driveway. I run in second gear after a min, step on clutch and still idles high at 1200rpm - 1300rpm until I come to complete stop, then the idle drops back to around 700rpm three to four secs after complete stopping-these symptoms are when cold.
When at running temp, she will idle reasonably well (around 800) if Im going up through the gears and step on clutch b/n 3rd and 4th gear. But if I'm cruising in 4th and come down to 3rd with clutch in, the idle stays up at the rpms that i was at when cruising (until I come to complete stop when the rev's eventually fall back to around 700rpm). If I down change in any gear, the same problem happens.
This problem seems to have gotten worse after a recent trip in the high country where the engine coolant temp got into the red range for a little too long. The engine is running rich (fuel smell at exhaust) and I have black exhaust tip. I know there is an exhaust leak around the exhaust manifold that needs attention.

FWIW, new IAC valve, checked for vacuum leaks (none apparent), checked all hoses, new water pump, new plugs, newish MAF sensor about 2 yrs old (reco), new thermostat. Otherwise, engine seems fine and compression seems good, no real loss of power under load.
Are there any 3.9 owners who could help me solve this one. I suspect TPS or VSS, but I don't know enough about these before I go swapping them out. Could a coolant sensor also be causing this..so many options.
Any help greatly appreciated. - Muddy 69

[DEFENDERZOOK]

<span style="color:blue">is your stepper motor functioning correctly and not seizing up....?

that controls idle.....</span>

[PhilipA]

It sounds like you have an automatic ECU in the car, as this is normal behaviour with autos to smooth the change to first as the car comes to a stop. The ECU takes a signal from the Vehicle Speed sensor to tell it whether the car is moving or not. If moving idle up , stopped then normal idle.
The cold start behaviour sounds normal to me.

I remember several years ago i had a Falcon auto which did this and drove me mad in traffic. Went to the dealer several times ( who had no idea) until I finally read that it was normal.
regards Philip A

[muddy69]

Thanks guys, but this is a 5 speed Manual 3.9 V8 injection. Not sure if the ECU is automatic or not..thats' too electronic for me..

And the stepper motor (ie IACV) is brand new from ULR in Malvern.

The idle is way too high as the idle prior to this wasn't too bad...

[muddy69]

Basically, the engine maintains speed with the foot off the accelerator only until the vehicle comes to a complete stop..

I want to change components out, but would like other people's opinions before spending big $$ unneccsarily.

[igould]

I've had similar (not identical) problems.
Mine would idle at 2500rpm until I had stopped for 20-30 seconds, when it would drop in steps down to normal idle. If I didn't get a long red light somewhere, it would continue until I had a chance to stop for a decent length of time.
I could be rolling along at only 5kmh, and it still wouldn't drop until I had stopped moving.
The general consensus here when I was chasing solutions seemed to be stepper motor problems.
Pulling the stepper motor off and cleaning it with carby cleaner has helped, but not completely solved the problem.
Since a new stepper motor is in the hundreds of dollars, I'm learning to live with it until it gets too bad to put up with.
Apparently, it's operation can be checked using Testbook at you friendly neighbourhood LR stealer.
I'd be interested to hear your solution when you find it. It may help me.

Good luck,
Ian

[PhilipA]

You have not mentioned the injection temp sensor. They only cost $30.
If it is rich and idling fast, it sounds like the ECU is cold compensating. Might only be a dirty connection. the resistance values are in the manual.

VSS should not be an issue. Does your speedo work?

TPS will not do this, usually anyway. Bad TPS most common symptom is miss while tipping in off overrun. In some circumstances, the car will cut out while just cruising along.
fuel temp sensor? This only compensates by a small percentage so should not cause the problem, but check the connections.

Bad IACV will usually cause stalling as you come to a stop as the car falls off high idle. the IACV on 3.9 is quite crude with I think only 4 steps. When they are dirty the usually just slow down in reaction, but should not cause avery high idle. What is the base idle?

Just thought of something. Could be a lot of crap around the throttle butterfly. Take of the rubber pipe and clean around the throttle blade, and take off the crankcase vent pipe and do the same.
This is my no 1 bet.
RegardsPhilip A

[muddy69]

Ian,

thanks for the advice. My symptoms are very similar to yours, but I can live with it no longer. The fuel consumption has sufferred a little too long. As I said, my stepper is brand new and the old one was suffering a little.

Philip, thanks for your advice. Come to think of it, i think i will replace the flame trap and crankcase breather components. it's time to renew them and the flame trap was a bit crudded up anyway. Will clean the butterfly housing also as i haven't looked at that. The fuel injection temp sensor is what I meant and not the coolant sensor. The high rpm/rev problem is temperature sensitive, thats why i suspect an electrical/sensor component.
I have no cutout at speed and agree with you that TPS possible not problem. VSS-Speedo works fine although there is boucing in the needle up to 60 kmh, probably twist in speedo cable though.
Base idle is meant to be 525 +/-25rpm, mine is def higher than that. Will let you know how I go...Muddy

[muddy69]

Philip,

Do you have the resistance values. I don't have a manual and only have Haynes to go by. Maybe need to invest in a manual!!
Muddy

[muddy69]

Well, I think I may have solved my own problem.
I had a fair bit of carbon buildup in butterfly housing of the intake. Cleaned as much as I could with a clean rag, squirt of WD 40 and she's idling much better. Still a bit high. Need to adjust idle speed once I go over a few other components.
I guess it pays to clean out the whole intake system and not to overlook any component.
Phil, those resistance values would be handy on the sensors if you have them..or tell me to go out and get a manual and stop being a tight ass

Thanks for the advice Phil..you are a legend.

[PhilipA]

I looked it up.
The value you need is that at 80C plus the resistance should be 300-400Ohms. So warm her up and then check with a multimeter. the sensor is only $30 from Graeme Cooper.
Regards Philip A

[muddy69]

Thx Phil

Will do. And will take the IACV off and give the shaft and chamber a good squirt of carb cleaner.

She's still revs high, but will clean it and check/replace the sensor and let you know how I go.

Muddy

[muddy69]

Phil

Just curious. Is the injection temp sensor the same as the fuel temperature sensor..I'm assuming it is..
Checking the US/UK websites, this part is $90 US. How come so cheap here in AU?

Muddy

[PhilipA]

The values are the same but they are different sensors.
The fuel temp sensor is attached to the fuel rail on a Disco I think half way along the LH side of the rail. It's a short button like thing.
The injection water temp sensor sits upright on the RH front of the manifold behind and to the right of the thermostat housing. it has an injection plug on it.
I think that the sensors are not OE but they work OK. Graeme Cooper does not tell where he gets them. Who knows why some parts are priced differently. maybe in UK they can only get genuine or they just are getting ripped off. For example teh IACV is the same as a Chev one.
Regards Philip A

[muddy69]

Phil,
Checked the sensors with my ohm meter. The fuel inject temp sensor is 120 ohms and the coolant sensor is 80 ohms.

Do I have faulty sensors?

[PhilipA]

No that is OK.
You worry if they are higher. They go up to 4000 Ohms or something when cold. Anything under 400 registers as hot and turns the choke off.
Probably if you turned the motor off you had heat soak which made the temp higher at the sensor
Regards Philip A

[muddy69]

I read that these vehicles have no requirement for adjustment of the base idle, but I just followed advice from tech section on atlantic british website and adjusted the base idle/hot idle.

have got it down to around 700-750 rpm and seems to idle better after running in traffic.
thanks for your help anyhow.

Do you know where i can get my hand on a workshop manual reasonably cheap?

[igould]

Originally posted by muddy69
Do you know where i can get my hand on a workshop manual reasonably cheap?
On the emporium here: http://www.aulro.com/modules.php?name=Shop...=category&cid=3 (http://www.aulro.com/modules.php?name=Shopping_Cart&file=category&cid=3)

Cheers, Ian

[muddy69]

Ian

The CD doesn't seem to cover the 93/94 model. Or is it a mis print. I'd assume my 94 would be covered. Do I need to know anything before getting the RAVE cd?

Muddy

[igould]

Originally posted by muddy69

The CD doesn't seem to cover the 93/94 model.

I must admit I never noticed that. I just checked my copy and it definitely says 1995 model year on.
As to any differences for earlier models, you'll need to consult someone wiser than I, such a PhilipA.

Ian