I have an unusual problem that no one on any forums has replied to. The engine surges with light throttle accelerating or cruising at 2000RPM after warming up to operating temperature. It has done this before and after an engine swap. Rather than live with the problem I've decided to throw parts at it. I made a list of parts that could be the cause that were not changed during the engine swap, and I've started to upgrade or replace them. So far I've done the fuel pump, fuel sock, fuel filter, ignition coil, ignition leads, spark plugs, O2 sensor, tried Sea Foam green, and some other stuff I'm forgetting. I still have my DX exhaust manifold on the Z6 engine. If there were a crack or leak in it, could that be the cause? What parts should I try next?

 

Engine shudders so bad I can feel it on the gas pedal. If I hold it low throttle at 2000RPM, it shudders until it upshifts and then it's smooth. Car runs great otherwise. What else should I throw at it? What should I check? AF ratio at WOT is great.

 

check vacuum hoses, throttle body and cable. Sounds like you have an auto tranny.
Have you checked the fluid?

 

Tranny fluid is brand new. No change before and after fluid. I cleaned the throttle body out. Vacuum hoses should be good, I'll double check and replace them.

The throttle cable is another story. I thought that the cable was binding when I had this problem that the idle would sometimes be about 300 RPM too high when coming to a stop. Then blip the throttle and it would return to normal. I tried lubing it on the throttle body side but that didn't help. When I got the new fuel pump and reset the ECU, this problem disappeared. As did my surging problem, but then two weeks later it came back.

I think the car is haunted. I hear chains dragging in the hatch sometimes. Must be Marley's ghost.

Thanks for your response. I didn't think I was going to get one.