Erratic idle

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waveyr02
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Erratic idle

Post by waveyr02 »

I have now got my synergie on the road and we think its great, but it has a problem returning to idle. Its when you lift the throttle it takes a long time to return,its idle is fine once there but its spoiling the driving (at rounderbouts etc ) just wondered if anyone could point in the right direction if they come across this before. Its a 2.0 8v petrol. Thanks Simon.
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Mandrake
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Re: Erratic idle

Post by Mandrake »

First thing I'd check is to make sure that the throttle plate is not sticking open at all - I'm not familiar with that engine but you should be able to slip off the pipe between the air filter box and the throttle body and visually watch the throttle plate turn as the accelerator is operated, and confirm that it snaps completely shut instantly when you take your foot off the throttle.

Also check the throttle cable slack adjustment isn't too tight, and if the inside of the throttle body around where the throttle plate seals is dirty with cabon/oil buildup, give it a good clean as a dirty throttle body can affect idle stability and the transition between idle and small throttle openings.

For example on my V6 a small throttle opening would actually cause the revs to drop below idle and try to stall, and I wasn't able to get a steady speed between 1000-1500 rpm with any throttle opening, it would either try to stall or jump straight up to 1500 rpm, and it would sometimes hang at 1500 rpm for a moment before dropping back to idle after being revved. Cleaning the throttle body and throttle plate cured those symptoms.

Those are the basic things that I can think of to check, there are a number of other things that might cause the engine rpm to hold higher for a second or two before dropping to idle, a faulty oxygen sensor can occasionally cause symptoms like this - the ECU gets confused by the faulty data from the sensor and will hold the revs higher (and sometimes cycle them up and down a bit) to try to clear the fault. A faulty throttle position sensor could potentially cause a problem too.
Simon

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waveyr02
Posts: 36
Joined: 23 Jan 2013, 18:20
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Re: Erratic idle

Post by waveyr02 »

Thanks for the reply i will have a look at the throttle body tommorow.
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