I have a 88 Camaro 305 with tbi and auto trans. Swaped out engine and trans due to high milage. Installed new engine and trans for the same year of camaro. Engine starts and idles perfect. Timing is spot on. No vacum leaks and the cat was replaced due to high back pressure. Engine pulls strong until floored. At this point engine light comes on and engine loses power. Idles becomes ruff and acts as if the timing has changed. Engine temp will start to run hotter. When the car is shut off everything returns to normal and the vehical runs fine untile you jump on it again. No readable codes can be recovered. Help!

 

a friend at work has a 3000gt with a similar problem...
his car would run good....and check engine light came on....and ran like crap...he bought an OBD2 scanner and it was his throttle position sensor.....
he could watch the voltage go from .1 at idle to 0 when the light came on...and jump back to .1 when the light went out.
no guarantees but just a suggestion...take the one out of yer old motor and try that one

 

Knock sensor mabye????