been having problems with my GSR, it has a few mods, but lately when i rebuilt the block, got a valvetrain upgrade, the new intake, etc. its been giving me problems. it missfires badly (enough to where it wont stay on, or very low rpm, like 400rpm) when its cold... but when it warms up, it idles at a steady 700-800rpm, drives fine, revs fine, and stays on by its self.

took it to a shop, and they said the aftermarket intake could be throwing it off, since on start up it smells like raw fuel, and it blows dark smoke out the tail pipe. rings are new so they said SOME dark/blue smoke is fine.

timing is set, MAP, IACV and fuel/spark are all dead on. block has 30 miles on it. head was rebuilt 5k miles ago. ECU is stock obd1 p72 basemap.

 

Was the ecu chipped?

 

Something tells me the problem might be associated with this part "when i rebuilt the block" these are the most reliable 4 cylinder motors on the planet.

 

Stock P72 ecu with mods do not go well. Especially with the single runner style IM.

 

I have the same problem I also have a gsr motor with a p72 with s300 and my car will not start right cold I have to give it slight gas until it warms up and then it will idle fine, but it will randomly fluctuate sometimes when it is warmed up it does sound like it is misfiring cold help this guy out

 

Sounds like you need to do a compression test.

 

I have the same problem with my 98 auto teg ls, idles ruff but when I start driving it's fine, on cyl 1 , when I take the spark plug wire or injector off it makes no difference !!!!