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Rough Idle on Cold Start

16K views 10 replies 7 participants last post by  yamahaSHO 
#1 · (Edited)
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?
 
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#2 ·
I thought this was normal. I went stage 1 yesterday and this morning starting my vehicle, my RPM was around 1500, never this high on stock. I waited 20-30 seconds and it was still at 1500, when i was at a stop after 5 -10 seconds of driving, it came back down to 800 RPM.
 
#8 ·
I have the same problem, cold start , protuned with following parts ,
Idle fluctuates from 1300rpms to 950 Rpms , trying to figure it out .


MegaMAF 73mm Big MAF
Perrin tubo inlet tube 2.4"
Blouch 20g-xt turbo ( 2.4" inlet , 10cm hotside)
ERZ 3" catted downpipe
perrin fmic
Tomei equal lenth header/Uppipe
invidia catback exhaust
grimmspeed ebs
deatschwerks 850cc injectors
deatschwerks dw65 pump (265lph)
Okada coil packs
Colder plugs (ngk 2309)
crank pulley
aos
Moshimoto radiator
Sunoco 93 octane
 
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