Rough idle at cold start
Thread Starter
Heel & Toe
Joined: Apr 2025
Posts: 15
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Rough idle at cold start
2002 C5 stock coupe with 104,000 miles and suddenly developed a rough idle when cold and definite engine miss or stumble. Smooths out after warmed up but after a 15 min highway drive at 75 mph and coming to a stop the engine shook then stopped and car ran fine. Looked but see no vacuum lines loose and plug wires all connected. No codes in dic either. Any suggestions on where to look would be appreciated.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,606
Likes: 4,060
From: Cape Coral, Florida
If you don't have at least a code reader I'd take the car to a diagnostic shop...they test and don't guess...could be a skewed ECT sensor...if a misfire can be a few things..."looking" to see if you have a vacuum leak isn't of much help...you can look at your fuel trims... that will help you.
