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Thread: Initial lumpy idle and slow initial throttle response?

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    Default Initial lumpy idle and slow initial throttle response?

    Hello everyone!

    I've just bought my Vectra C a couple weeks ago and I have noticed that when i first turn the car on, the rev counter drops to around 600 revs then the car automatically adds some throttle bringing it back up to 1500 revs, then it drops for a second time (sometimes a third), and goes back up to 1500 again before finally resting at a normal idle rev..

    I know i'm a new drive but this seems slightly odd to me.

    Also, when I put my foot on the accellerator sometimes the car takes up to a second before it responds and the revs start going up.. similarly, sometimes when i take my foot off the accellerator it can take up to a second before it responds and the revs start going down again.

    Also, seems odd to me.

    Thanks to wotsthestory - He plugged his Tech2 into my car and pulled up a fault code, " P0170 - Fuel Trim System Lean " - He's told me that he thinks it might be related to the Idle Air Control valve, but advised me to make a post to see if any of you more mechanical bods might know any better.

    So, any ideas?

    Thanks.

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    Regular Member wotsthestory's Avatar
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    It was the first thing that struck me having seen it another car, clean up the throttle body. I wasn't sure if the IAC valve is serviceable on it's own, or needs the whole throttle body removing and cleaning up.

    Also, his diagnostic port was over to the left, we had to remove more trim to get to it, whereas mine I just removed fag tray and it was in the centre.

    Bri

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    any advances on this one guys?

    I haven't had any time to clean out my throttle body yet but it's on my to do list!

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    Regular Member Dose's Avatar
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    Clean the throttle body, a proper good clean with carb cleaner? am guessing yours is a 1.8?
    My one was pretty much the same,

    The IAC is built into the throttlebody

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    I had the same problem on an astra. I put the op-com on it and watched the live data. I noticed that 1 of the oxygen sensors on the exhaust down pipe was constantly flicking between lean and rich and showing an incorrect voltage. I replaced the oxygen sensor and the car ran as good as new. I hope this helps.

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    Regular Member wotsthestory's Avatar
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    Worth a check I guess, pop your car back over and we'll check live data.

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    When your watching the live data watch both the oxygen sensors and see if there is a big difference between the time they either lean or rich the fuel mixture. Also see the voltage of the sensors and see if there is any difference between them.
    One of the sensors is located at the very top of the exhaust down pipe and the other is located under the engine near where the down pipe joins the main exhaust.
    Hope it helps mate

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    Regular Member rushy's Avatar
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    What engine is it?

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    it's a 1.8i

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    Regular Member rushy's Avatar
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    Could be the MAF or air leak on the intake system. Check the intake manifold is all tightly bolted to the head, check all the intake pipework is air tight from the MAF to the TB and that the TB is seated properly. Try buying some Carb cleaner, take out the air filter, get someone to raise the revs to about 2000-2500rpm and blast the cleaner up the intake, this should help clean the MAF and TB, but TBH the best way is to take them off and do it by hand but the MAF can easily be damaged.

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