How do I test Idle Control Valve

[Mike Young]

Hi

I've got an '88 Carrera 3.2 with an idle problem.

If the engine is running above 2000 rpm and I take my foot off the throttle, the engine speed will drop to about 1000 rpm quickly then something seems to arrest the deceleration and hold the engine at its idle speed of about 900 rpm.

If the engine is running below 2000rpm then when I take my foot off the throttle the engine speed drops to about 100 - 200rpm sometimes cutting out and sometimes recobvering to idle properly.

This happens with the engine hot or cold.

I've tested the throttle idle switch - that is OK
I've taken apart the Flow meter and checked the pot with a meter. Thats running smooth and no apparent problems.

I've also checked the Idle Control Valve. This particular one has three connections unlike some I read about that have two.
The valve body seems free enough to move but I dont know how to check the part fully.

Can anyone help please?

[Rot 911]

The search button is your friend:
3.2 Idle Problems
and here
and one more

[Mike Young]

Thanks for the pointers Kurt. There were some good points there and I think I now know how to test the valve.

But something else is bugging me! Its all too predictable.

When the engine decelerates from above 2000 rpm it stops SUDDENLY at about 1000 rpm and then idles fine. It sounds like there's a surge of power from somewhere that halts the deceleration, and its this surge thats missing when the engine speed starts to drops from below 2000 rpm.

Can anyone explain whats going on in the Motronic system when changing from normal running to idle? What initiates this surge

Mike

[Mike Young]

Iv'e just unplugged the idle control valve and tried the engine. The problem has gone away. I guess I need a new valve then!

BUT it seems to run fine without the valve at all- whats its purpose ?

Mike

[Tim Polzin]

Don't throw away the ISV as it sounds like it is working. It provides bypass air to keep the idle constant. Give it a good cleaning with carb cleaner or the like, then adjust the idle based on these instructions from John Walker on a previous post:

"are you using the screw on the throttle housing that faces to the rear? a 7mm deep socket works well to turn it. if you have an old black, round relay, you can pop off the cover and use it as the bypass tool. plug it in the receptacle on the left side of the engine compartment. push the tab on it's electromagnet with your finger. you should not notice a change in idle speed when you push the relay tab. if you do, raise or lower the idle speed until you don't notice a change."


Tim

[Mike Young]

Thanks Tim

I just tried linking the test plug to disable the ICV and the engine speed drops very low - almost cutout. So according to the info by John I need to adjust the idle to about 850rpm with the ICV disabled.

I'm a bit unsure about the idle adjustment screw !

I couldn't find the article you refer to by John and I'm afraid to start adjusting screw without being sure I have the correct one.

Can you point me to the correct article or even describe the idle adjustment screw on my '88 3.2 carrera

Thanks
Mike

[Steve W]

I've posted a basic idle adjustment procecure at the bottom of the following page along with pictures and diagrams. Good luck:

idle speed adjustment

[Mike Young]

Thanks Steve

I took a guess at which was the idle speed adjustment screw yesterday, and give it a go. When I disabled the ICV with the link, the engine speed dropped very low and almost cut out. I then adjusted the idle speed back to about 900rpm using the adle adjust screw and removed the link.

Amazing, the problem has now gone away and my carrera drives great for the first time since I've owned it.

For anyone thats interested - on my way to getting this fixed the ICV was my main suspect. I'd cleaned it out as commonly suggested on this Forum, but my idle problem didn't go away. On the point of buying a new one I thought nothing to loose and took it apart, cleaned up the considerably scored slip rings with a very fine wet emery cloth and put it back together.

What I'm trying to say is for someone with a suspect ICV, you can take these valves fully apart and service them more thouroughly than just a squirt of carb cleaner.

I've posted a thank you to all at the following link Thanks for your help

But thanks again everyone for your help

Mike