D2 Hunting Idle - annoying

[astormsau]

hi everyone
prior to my lpg install the disco was running a bit rough at idle and not performing as well as it should have. the LPG install i recently had done has made no difference to the idle on petrol and gas exhibits the same behaviour.

When stationary in Drive or Park with aircon off, the idle will sit around 680-700 rpm with the top side of the tacho needle level with the bottom of the third marker (i assume about 680-700 rpm - assuming the markers are 0, 250, 750, 1000).

The idle speed is fine and seems inline with specifications, what happens though is that the car hunts around, up and down about 50 - 100 rpm. If you sit there you can hear the revs dropping and then going up, ever 2-3 seconds. Its only about 50rpm but noticeable and sometimes its more pronounced than other times - maybe dependent upon the weather but running on LPG or petrol makes no difference (i have a vapor injection lpg system fitted). It will exhibit the same behaviour on either fuel.

In the last month i have;
-replaced the MAF with new genuine MAF and had it checked to ensure the new one was ok
-replaced passenger side oxygen sensor - testbook found it faulty
-replaced ignition leads with bosch leads suited for gas
-replaced sparkplugs with NGK BK6 plugs
-replaced air filter element
-replaced engine oil and oil filter
-ran Wynns injector cleaner through a full tank of petrol

So i have taken alot of the steps one would normally take to diagnose this kinda problem. Ritters in Melbourne replaced the ignition leads after I had done the MAF, oxy sensor and plugs and checked and verified that there are no faults showing in testbook.

Just wondering if anyone else has this issue, the car never stalls and does not idle in a very erratic way (up and down from 1000 - 2000 as some people with D1's have found). When i start the car when its cold, it idles at 1200 rpm for 20 seconds as it should, then drops to about 900 rpm once its a bit warm and then ends up sitting around the 680-700 rpm mark so I know the IACV is at least functioning to control idle speed in some way.

I put the old MAF back on (the original which came with the car), it caused the car to idle at about 500 rpm which is too low, but it was still hunting around a bit... up and down by about 50 rpm and of course, not performing as well as it should because the MAF was dead.

I am wondering if the IACV is dirty or if the throttle body could need a clean? I assume you do this with carby cleaner.

Any help/experiences or instructions would be great.
Thanks
Andrew

[mike 90 RR]

At the back of the pletium you have a stepper unit .... This controls the air flow for idle ... Take it off & clean it with carby cleaner .... Make sure you install it back with CLEAN & FLAT mating surfaces ....

After that check for vacuum leaks ...

Also check your vacuum advance on the dizzy is not stuffed ... take off the black vacuum line & suck on it ...

Mike


:)

[astormsau]

hey mike
thanks for the advice, unfortunately i dont have a dizzy or a stepper motor
Discovery model 2's have an IACV which is an idle control valve which is magnetically driven to control air flow, i am wondering if this needs a clean. and no dizzy unfortunately, only coil packs.

[mike 90 RR]

hey mike
thanks for the advice, unfortunately i dont have a dizzy or a stepper motor
Discovery model 2's have an IACV which is an idle control valve which is magnetically driven to control air flow, i am wondering if this needs a clean. and no dizzy unfortunately, only coil packs.

Yep ... forgot about that (coil packed) .... But the "magnetically driven to control air flow" unit .... Have a look at it

In the earlier versions I would clean the wire mesh of the "Hot Wire sensor unit" of any grease and grime with a spray can of "Electrical contact cleaner" (located between air cleaner & manifold butterfly control) ... & clean the "stepper unit"

The other is Air leaks (manifold / lousy vacuum hoses )

Mike

[astormsau]

hi Mike
i cleaned out the IACV magnetically controlled air valve last night, gave it a good soaking in contact cleaner (as i didnt have any carbie cleaner) and the valve is now moving a lot free'er now than it was, plus got some muck out of the pipes leading to and from the IACV.

Put everything back together and the hunting idle problem is still there. The car still idles up at cold and when accessories are turned on,etc but its still hunting...

any more suggestions? any chance the throttle body would need a clean?

thanks for your replies
andrews

[mike 90 RR]

hi Mike
i cleaned out the IACV magnetically controlled air valve last night, gave it a good soaking in contact cleaner (as i didnt have any carbie cleaner) and the valve is now moving a lot free'er now than it was, plus got some muck out of the pipes leading to and from the IACV.

Put everything back together and the hunting idle problem is still there. The car still idles up at cold and when accessories are turned on,etc but its still hunting...

any more suggestions? any chance the throttle body would need a clean?

thanks for your replies
andrews

Sorry Andrew .... on the electrical side I am out of ideas .... But never hurts to clean all parts

However .... If you you are looking for a mechanical fault that can cause this problem .... Then it would be a slack CAM chain

To test ....
Remove spark plugs
Remove rocker cover / (left side?)
Put "socket with solid bar" on the crank bolt
Line up crank to the TDC mark
Then move the crank backwards / forwards & watching the rocker move
You should be able to feel the amount of "slack" in the chain and record "How many degrees" is the chain out?? (due to slack)


I have fixed rough idle / Hunting Idle problems ... but this is when the motor is at the 180,000 K mark .... When I test the chain if I record a movement of 6 degrees = replace (It's shot) .... The cam chain should have basically, no movement when new


The cam is spun backwards & forwards on a slack chain (as it is trying to play catch up) of TDC ..... which throws the electrical timing and also the cam duration peak's of "open & closed" out of sinc with the position of the piston
Also other dependents of the "chain" are computer & EFI


How many K's has yours done???

Be aware that I am not a Qualified Mechanic .... Just your average bloke with a shed and a bench full of tools


Hopefully others will add to any other Ideas :angel:

Mike


:)

[astormsau]

hey mike, its only done 127,000kms.
Motor is strong and performs well, its only the idle which is off.
Because it performs well i have discounted the coil packs as faulty as they seem ok. The only other thing i can think of is the throttle body being dirty or... the ACE (Active cornering enhancement) pump causing it to idle around a bit as that draws off the motor....

Andrew

[mike 90 RR]

hey mike, its only done 127,000kms.
Motor is strong and performs well, its only the idle which is off.
Because it performs well i have discounted the coil packs as faulty as they seem ok. The only other thing i can think of is the throttle body being dirty or... the ACE (Active cornering enhancement) pump causing it to idle around a bit as that draws off the motor....

Andrew

Never hurts to check the CAM chain .... Cheap to test (free) It's good to eliminate it because electrics cost $$$
You don't have to take rocker cover off ... just the plugs .. because if you are OK with mechanics, then you will still feel the slack

I think on the coil pack note .... My understanding of them is they that either work or don't // no gradual decline of performance (knowledge based on my 95 fairlane with coil packs) But i think you have stated that mechanic has tested all this side??

What are the type of spark plug & number are you running???
Make sure you have the right ones in because there are 2 types & one of them is a "resistored type" (self cleaning // I think this is the one for your model) ..... The correct one should be listed in your "owners manual hand book"


Mike

[astormsau]

mike i went from running good old OEM platinum plugs to NGK BK6's because im on LPG.

Same idling issue on both sets of plugs - apparently the platinums were in good condition when they came out, but they run a bit too hot for gas hence the BK6's which are a cooler plug.

I will get my brother to look at the cam chain sometime as he is mechanically minded!

thanks
andrew

[ozscott]

The Bosch Motronic likes Champion double platinum OEMs and OEM leads. I run them with the original coil packs and LPG/Petrol in my D2 - 125,000k...very smooth. Mate all I can suggest is checking for leads and sticking to standard plugs.

Cheers