fluctuating RPMs on 3b 20V?

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Nov 4, 2003 | 05:56 PM

feelstranger

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fluctuating RPMs on 3b 20V?

Hey all,
first thing to figure out on the new 1991 200 TQW. It has an odd fluctuating rythmic hesitation when driving constant speed- just enough to feel. Then I found that when stopped, if I step on the gas and hold it steady around 2K-3K rpm that the rpms will begin to drop several hundred rpm for a few seconds then come back up, and then drop again, and so on -in a cycle. It'a about every 5 seconds or so...
This is not apparent at idle.
Any ideas?

Nov 4, 2003 | 06:36 PM

devil's advocate

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could be

an undercharged AC system kicking in and out. Try turning the climate control to "econ" and see if it still does it. Even in cooler weather the auto climate control will run the ac (unless it is below 40 degrees or so). If the system is undercharged it will cycle on and off because it has a low pressure cut-out switch.

Nov 4, 2003 | 09:24 PM

RockinV8Q

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O2 sensor

RPM fluctuations of several hundred RPM under no-load steady throttle indicates an 02 sensor on its last legs.

Nov 4, 2003 | 10:31 PM

sk88erguy

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thats what i replaced when mine did that and it fixed it for the most part

it still does it very mildly, maybe only 2 or 3 times sinse i replaced it and it has been a while but ya that is it, i think i might have some old wires going to it causing it to surge very slighty when it does.

Nov 5, 2003 | 06:44 AM

feelstranger

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Thanks for the info-

It was on ECON during the observations....
Could the O2 sensor cause the hesitation under load also?

Nov 5, 2003 | 09:42 AM

RockinV8Q

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Re: Thanks for the info-

Yes it can cause fluctuations under load.

Nov 5, 2003 | 10:12 AM

5kcstq

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I noticed something similar

I've been driving my 200q20v for only a week now, and I noticed that during steady state throttle, or very slow, gradual, acceleration I can feel the car almost surging. I haven't noticed the big changes in rpm's you describe, and the frequency seems faster.

Mine seems like it's going a tiny bit faster, then less fast, then a tiny bit faster, etc.

I asked an Audi tech friend of mine and he said that's how the cars are. However, your symptoms sound different than mine.

I just passed smog and I haven't had any other strangeness, but maybe a new O2 sensor would help (my problem).

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Nov 6, 2003 | 02:10 PM

5kcstq

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Re: I noticed something similar

Yeah, probably two sides to the same thing. If I was accelerating and it didn't, I would call it a hesitation, or a stumble (altho' stumble sounds even worse). When I try to maintain the same speed, the car likes to sort of go/rest/go/rest.