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After extensive searches, I do realize that this is a loaded subject. I recently installed 740cc Nismo injectors, and Ash-Spec ECU. My first plenum pull, but have reasonably good experience with automobiles. All went well, replaced a ton of old hoses and such, performed a coolant bypass, used all new injector seals and properly lubed. Problem now is that the idle is noticeably rough. It’s not so bad that the whole car is shaking terrible, just noticeable. Here is the breakdown so far: - No codes (55)
- Rough idle in only when engine has warmed. Exhaust sounds as if there may be a slight misfire.
- At cold startup the engine is perfectly smooth, and has absolutely no indication of a misfire at the exhaust.
- Drivability is normal. Runs smoothly through gears, and boost is good.
- Has good vacuum. Searched like hell for a disconnected vacuum line, but none. (I labeled and tracked everything through the job, and all connections were accounted for)
- Injectors were checked for resistance and all a perfect 10 ohms.
- Performed power balance test. All cylinders firing, with no noticeable culprit cylinder.
- Gas mileage is at about 19mpg in town. Haven’t measured highway yet.
- TPS is functioning correctly
- I disconnected the top IACV connector (yellow), and had no change. Didn’t disconnect the bottom (blue) connector. Most likely not this, as the idle is rather steady.
- Disconnected the air regulator, and had no change.
- I’ve had a compression test done in the past and all is good. Besides this issue would have been there prior to the plenum pull. Car only has 65k miles as well. Car ran perfect before this job, so it is hard for me to believe that parts not touched suddenly went bad. A vacuum leak is usually the culprit for this kind of thing, but what throws me is that it runs perfect when cold. Other ideas? Thanks in advance and sorry so long.
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