Runner1954
New member
I have a stock 2009 corvette, no modifications with 50,000 miles. I do have a GM extended warranty. My car started to idle rough in Aug 2016. I've completed the normal maintenance stuff and replaced plugs, wires, coils, coil wires, engine upper intake flush and fuel tank flush per GM. MAF sensor was also checked out. My initial post in Dec I described a rough idle issue, no codes. Took my car to the dealer with negative results. I contacted GM and was advised with no codes I could not be helped. Jan 2 2017, I took the vehicle to another shop and after checking my car out the shop came up with two codes P0300 and P0357. My car will idle for 10 seconds at a stop light and its fine, then the rough idle starts where the RPM needle jumps. You can feel the engine rock a little/ rough idle. On a normal 30 drive in stop and start traffic 20% of the time the idle is fine and 80% rough with the RPM needle jumping slightly. The car drives fine with power no hesitation. I returned to the dealer and my car has been there a week with still negative results. The tech advised me that the codes are in the history but not current and the idle seems fine. The service manager is trying to come up with a solution but working with GM I'm not confident he will. Any ideas?