Fluctuating Idle when coming to a stop
11-29-2016, 08:20 PM
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Fluctuating Idle when coming to a stop Hey guys hope that you're all doing well, but basically I bought a 2002 WS6 a few months back and as of recent have been noticing that when doing a cold start it'll start up and idle near 1000-1200 (where it typically idles at about 800) and even once it has warmed up sometimes after coming to a light it'll stick around 1000 again or sometimes it'll lower down to 600 or so. I can't seem to find a pattern to the behavior and about half the time its right where it usually is at about 800. I thought maybe the MAF sensor so I cleaned that out and while i had the thing apart I cleaned out my throttle body. Possibly a vacuum leak? It just seems random and I'm hoping you guys might have some insight into the problem. If its any help the car has ~116k miles on it but has been pretty well kept with the only other issue being a slight rear main seal leak that'll get to when I go and grab a new clutch to put in
11-30-2016, 03:04 AM
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The 1000-1200 idle speed on a cold start (especially in cool weather, where it will remain that high longer) is normal and part of the factory tune.
Once warmed up, if you have factory tuning then your idle speed is as follows:
M6: 800rpm
A4: 650rpm in P/N, 550rpm in gear
The above numbers are true and correct for every trim level and model year of LS1 F-body. The factory tach can be off by as much as ~150rpm at idle speeds, only a scanner will show true idle speed.
Having said that, the surge/high or low idle once warm is a fairly common problem but there is more than just one possible cause. Could be a dirty/dying IAC motor, a vaccum leak (PCV system is common, or sometimes an intake gasket), a TPS sensor issue, or even relating to the EVAP purge. Not all of these will trigger a MIL/SES, all depends on failure type/how bad.
Have you scanned for codes (pending or current?) Is the car modified in any way, and/or do you know if it's ever had a custom tune?
Once warmed up, if you have factory tuning then your idle speed is as follows:
M6: 800rpm
A4: 650rpm in P/N, 550rpm in gear
The above numbers are true and correct for every trim level and model year of LS1 F-body. The factory tach can be off by as much as ~150rpm at idle speeds, only a scanner will show true idle speed.
Having said that, the surge/high or low idle once warm is a fairly common problem but there is more than just one possible cause. Could be a dirty/dying IAC motor, a vaccum leak (PCV system is common, or sometimes an intake gasket), a TPS sensor issue, or even relating to the EVAP purge. Not all of these will trigger a MIL/SES, all depends on failure type/how bad.
Have you scanned for codes (pending or current?) Is the car modified in any way, and/or do you know if it's ever had a custom tune?
11-30-2016, 03:46 AM
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A few months ago I had a p430 code for the catalyst converters so I took out the O2 sensors and cleaned those out and the code has yet to come back. Just a week ago I had a p442 P code which seemed to be remedied by just tightening down the gas cap a little bit more. It is entirely stock and as far as Im aware it hasn't had a custom tune before.
Last edited by epicsockzebra; 11-30-2016 at 04:31 AM.
11-30-2016, 01:53 PM
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Which O2 sensors did you remove and clean?