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So, I'm having this ongoing battle with Joe's 164, an '89 V6, manual.

When cold the engine idles nicely. When warm the idle speed is around 1000RPM. It idles smoothly and drives smoothly.

Unplugging the idle air valve causes a stutter, then increases the idle speed further.
I have put several turns of tape around the grommet and made the clamp a tight fit.

Unplugging the throttle switch increases the idle speed, so that is also set correctly.

I have pulled off the chrome pipes and found leaky gaskets. I refitted the pipes several times with different sealants. Spraying brake cleaner around them caused a stutter. Eventually I removed the fuel rail and repaired stripped threads for the chrome pipes. Cleaned everything up and fitted new gaskets, new bolts. Spraying brake cleaner around no longer causes a stutter, engine runs a little smoother. Still no change to hot idle speed.

Never had this problem until I cleaned the throttle body. Throttle stop screw is backed right off and throttle cable is slack. If I press the throttle plate HARD closed, idle speed drops.

Also cleaned and refixed pipes for oil vapour separator. Removed and inspected corrugated pipe and refitted with great care to ensure all pipes fitted tightly with new clamps. No change.

Tried removing/plugging lines to brake servo and fuel pressure regulator. No change. Even replaced oil filler cap and dipstick O-rings in case air being drawn through crankcase.

Going to try a spare idle air valve and slacken/retighten throttle plate screws. Also thinking of swapping throttle body for spare but I can't see that making much difference, I didn't think the throttle had to be pushed so completely closed.

Running out of patience and ideas, any advice welcomed!

Thanks for reading,
-Alex
 

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You got a sticking or bad min max throttle switch or mis-adjusted one me thinks, or wring/connector going to it.
 

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Somehow it seems like it's getting too much air. Is it an electrical or a mechanical issue?

Back when I had idle issues and the mechanic left them worse than before, I obtained a Lancia manual. It said the throttle plate had to be shut as there was a factory adjusted stop that let a set amount of air in. As mechanic had messed with a adjustable rod linkage between throttle plate and the same sort of throttle position switch the V6 has, I had to take the rod out and adjust so the throttle plate would hit stop.

I then reattached a vacuum hose I found loose under the manifold and adjusted the idle to 750 rpm with the idle air adjustment screw. When I plugged the IAC valve back, it didn't rev up the engine, so I thought it must be dirty and sticking. Indeed it was full of gum.

The things that caused the problem were: a maladjusted rod and consequently maladjusted throttle position sender, a sticking IAC valve, a vacuum leak hidden in the guts of the engine and a mechanic not knowing proper procedure.

Also, I found the temperature sender wire had lost the retaining spring and would make odd contacts if touched.

Now that the IAC valve isn't sticking anymore, idle goes to about 1100 for a few seconds and lowers to 750 as it warms up. It is dead smooth and with 98 petrol, I can hardly tell it's running.
 

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To confirm (or otherwise), can you buzz out the idle switch with a meter to make sure the 'idle' contact is shut with throttle shut. I know you can hear them click, but best to buzz it just to be sure.


Your IACV sounds OK. The fact it speeded up a bit when you unplugged it, suggests it was already set to minimum air by the ECU, which probably exonerates the idle switch as well TBH - they have a limp-mode in that with no power applied, they should spring back past minimum air to a point where more air passes through. (I'm putting it badly - basically, they need a wee bit of drive to give minimum airflow)

Next, probably going to be the throttle plate I'd suspect as it does sound like you've sorted every other possible issue. Forgive the question, but did you put the plate back in the right way round (it has a slight chamfer to it), and did you tighten the fixing screws with the abutment screw backed right out and the butterfly pushed hard-shut (forcing it to align correctly)?. No doubt you did.....but have to ask just in case - don't intend any offence.

Other random and probably irrelevent thought - does the car think it has the A/C on by any chance? If pins 29 & 32 see 12V, the ECU will lift the idle speed to compensate for the A/C load.....but I don't think this is likely to be it.

HTH.
 
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