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Old 09-01-11, 03:58 PM  
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Default Rough Idle on Cold Start

My 2011 STi, on cold starts only, has a rough idle and some sputtering sounds. RPMs jump to about 1500+. After approximately 20-30 seconds everything smooths out and goes away. No driving issues. It only happens on cold starts. This issue has been going on for a while now but has been barely detectable (mostly sound change from exhaust) and not bothersome. I recently got protuned on E85 and the issue seems to be exacerbated. I did quite a bit of googling and searching and can't find a definitive answer.

During the protune we found a minor vacuum leak from the GS AOS main O-ring during a smoke test. It was the only leak. I've since sealed the leak. However, the issue has not gone away.

Just to eliminate possibilities... again, system was smoke tested. No injector leaks, no intake leaks, etc... MAF sensor is clean. Protune went well and no issues on the dyno. No smoke from tailpipe or under oil cap. No obvious fluid leaks.

Mod list:
- AEM Cold Air Intake
- Cobb downpipe
- Borla catback exhaust
- Grimmspeed air oil separator
- Grimmspeed EBCS
- Injector Dynamics 1000cc injectors
- Aeromotive Stealth 340 lph fuel pump

Any ideas?

Last edited by xatnys; 09-01-11 at 04:13 PM.
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