97 rough cold start - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 08-10-2009, 01:14 PM   #1
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Angry 97 rough cold start

My 97 non SC has developed a rough cold idle. It feels like a misfire for the first 10-20 seconds upon initial start, idles around 6-700 rpm,then it clears up and runs fine. No problem from hot start, just cold. I did plug this weekend but no help. It had the intake done on ot 2 years ago when I bough it.
I also get the occasional P0440 engine code, I clear it with my scanner then it is fine for a few weeks then comes back on. I also put new gas cap on just in case.
Any ideas on this issue.

Thanks, Martin

moved to 92-99 Toddster
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Old 08-10-2009, 01:46 PM   #2
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Might be your intake air temp sensor. Could be a dirty throttle body, clean the MAF, check the PCV valve, check for vacuum leaks.
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Old 08-12-2009, 12:16 AM   #3
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Sounds like the upper intake may be leaking coolant into the cylinder(*)
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Old 08-12-2009, 07:50 AM   #4
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Originally Posted by L67SE View Post
Sounds like the upper intake may be leaking coolant into the cylinder(*)
Not the usual symptoms though. Usual symptoms being cold are hydrolocked motor that won't turn over, or running better than warmed up. A leaking UIM will typically spew coolant as the system pressurizes or have filled the cylinders from the pressure of having been run and shut down.
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Old 08-12-2009, 08:39 AM   #5
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I could easily be wrong about Martman'* car. I just know that one of my previous Bonnevilles would do this and it was coolant causing the missfire. Seems the leak wasn't enough to miss hot but would leak when the car sat and cause a miss for the first 10-20 seconds of running. Replacing the UIM fixed it.

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Old 08-12-2009, 08:47 AM   #6
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I also had one of my Bonnevilles run rough cold and a MAF cleaning fixed it.
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Old 08-13-2009, 11:35 AM   #7
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Well, I did the plugs, wire looked original so I replaced them, tested the coils all was ok. Took for test drive and wow a lot more power. But still the rough cold idle. So I started digging deeper, and I pulled out the IAC motor and it was all carboned up, so I cleaned the intake system etc, and it is much better now. Thanks for all the good advice.
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