I installed a good used motor in my 93 single turbo car and I can't figure out this backfire at idle? Scrapped the vacuum tree and ran new vacuum lines to fuel pres. regulater, boost sensor, blowoff valve, and wastegate. I also have all sensors needed hooked up but still can't figure out problem. I ported the upper and lower intake manifold, removed the secondary throtle valve in the intake, pulled the oil needle and seat out off the front of the crank shaft and plugged it with the correct size bolt so it will inject oil on the rotors at all times and I removed the fuel mixing plates under the injectors. When I start the car it idles up to 2800rpm and sounds good for the first 30 seconds then it starts backfiring. I try to give it throttle and it just backfires and dies. Any ideas? Any help would be greatly appreciated!!

 

I just pulled the upper intake off to check vacuum lines, and I noticed that the intake runners are perfectly clean on the small primary runners but the big secondary runners are very oily and carboned up! The runners were perfectly clean from the porting so this is a major buildup in only the big secondary runners, and the gummy shitz goes all the way to the 2 upper throttle blades on the throttlebody! The primary runners are spottless all the way to the primary throttle blade. I removed and blocked all EGR and all PCV recirculation. Ideas

 

i had that once and i just reset the ECU, so try just taking off the neg cable and holding the brake down for 20sec and putting the neg cable back on and start her up and see what happens.

 

You have to hold the brake down for 20 secs to reset the ECU?

 

I will try resetting the ecu this weekend but the car has been apart for half a year and this computer is new? Thanks for your time!