Thread: Idle Problem

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

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

Originally Posted by 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

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?

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.

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.

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.

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

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.

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.