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Hello, I was wondering if anyone could tell me a thing or two about this rather bizarre problem I've been having with my car. It's frustrated me to no end, and confused my mechanic too.

I have a 1990 9000s, normally aspirated 2.3l, auto, with direct ignition. It usually runs just fine, except for the following:

When the engine is cold, no problem. When the engine warms up to operating temperature, still no problem. If I let the engine warm up and then turn it off for a few minutes, then turn it back on, some strange things happen. When I let the car "creep" forward, with or without my foot on the brake, the RPMs will drop down to about 100, then shoot back up to around 1500, and repeat the cycle a few times. I've heard this is called "loping" or "coughing".

I've been in and out of the garage because of this, and had the following service performed:

Cleaned out Idle Air Control valve (twice, I think)
cleaned throttle body, intake manifold, and valves too, I believe.
General tune-up.

None of this seemed to alleviate this problem, although the tune up and cleaning made the car perform better otherwise. A mechanic I talked to said it's because the engine computer is trying to figure out whether to allow lots of air in, or to close off the idle valve, when I "creep" forward. He said he would check through service bulletins for any way to adjust the engine computer or fix this problem.

Has anyone else experienced this? Is it an easy fix? Any ideas?

cheers
 

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I had a problem with my auto once, but it was going between idle and about 2500. It was one of the rubber sleeves in the inlet manifold that had come out, but if it's worn and a sloppy fit it may cause a similar fault. Apart from that I don't know off hand.
 
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