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rough idle at cold startup

 
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schwebby
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PostPosted: Wed Aug 10, 2011 11:28 pm    Post subject:  rough idle at cold startup Reply with quote

hey guys - I'm experiencing a rough idle for about 30 seconds or so at cold startup - after 30 seconds or so it runs like a top. I just had the plugs, wires, intake cleaned about 1800 miles ago - new fuel filter about 3000 miles ago. I checked under the hood when i start it cold and it sounds like it might have a vacuum leak - kind of a hissing/whining noise under the hood but like i said it goes away after 30 seconds or so - so it has been tough to locate. also, it seems if i rev it up just a little bit at cold start up the rough idle will clear up. Just wondering if i'm on the right track as far a being a vacuum leak - or could this be a fuel pressure regulator or MAF issue?

Thanks in advance

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barnettimpala
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PostPosted: Thu Aug 11, 2011 4:32 am    Post subject:   Reply with quote

This is what I would do:
1.) check for a vaccum leak first, just by checking th hoses and such.
2.) wiggle and clean the connector for the MAF.
3.) clean/replace IAC, which you should do as a general maintenance thing after awhile anyway.
4.) Now I would be considering a FPR.

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Albert2kls
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PostPosted: Thu Aug 11, 2011 9:02 am    Post subject:   Reply with quote

Mine was doing that last week and when I pulled the IAC out it looked like crap, I put a new one in $30.00 at Autozone and 5 minutes later it has not done it since.

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schwebby
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PostPosted: Fri Aug 12, 2011 1:23 pm    Post subject:   Reply with quote

thanks for the tips - I checked the MAF connector - I will check the vacuum lines and change out the IAC and see if that does the trick.

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schwebby
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PostPosted: Tue Aug 16, 2011 12:43 pm    Post subject:   Reply with quote

well - on Sunday I took the MAF out and cleaned it up - the 3 sensors were quite dirty. I put it back together and tried starting it and there was no rough idle. Started it again Monday morning and no rought idle. Started it Monday afternoon and the rough idle was back. I went to AutoZone and picked up an IAC and changed that last night - seems much smoother now - but i will have to wait and see - I hope this was the culprit - got a long trip from green bay to the michigan race this weekend so i hope she is good to go!

thanks for the help guys

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schwebby
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PostPosted: Wed Aug 17, 2011 6:30 pm    Post subject:   Reply with quote

update - after replacing the IAC i still had the rough idle at cold start up and the hissing sound near the air intake/drivers side headlight area. But once it is warm she runs like a top. Went and picked up a FPR last night (i could smell fuel in the vacuum line but it was not wet) but i was not able to get the flare nut off the FPR without taking the TB or the whole intake off - so i threw in the towel last night and brought it to the garage - they put the FPR on for me - not cheap of course - then when i just went to pick it up this afternoon it STILL had the rough idle and hissing noise by the air intake/drivers side headlight area.

I am baffled - i think i'm going to dig into the headlight fender area and see if i can find any vacuum hoses in there?

any other ideas?

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barnettimpala
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PostPosted: Wed Aug 17, 2011 6:49 pm    Post subject:   Reply with quote

Well, now that you mention where it's hissing, that sounds like a sound to do with the air inlet/intake/filter. Don't know why that would cause a rough idle tho.

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PostPosted: Fri Aug 26, 2011 1:04 pm    Post subject:   Reply with quote

just an update - the impala made it to michigan and back without any issues - although i still have my rough idle at cold start up. I have noticed the cold start idle is pretty smooth in the mornings when it is cooler out - but after work when the car has been sitting in the sun for hours the rough idle is the worst. (temps have been around 75 - 80 degrees in the afternoon). The chevy garage wants to look further into this for me (free of charge ) so I will have them look it over on the next oil change and keep you posted.

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