wildberryeagle

I have a 1995 z28 and I just rebuilt the lt1 and put a rebuilt 4l60e with shift kit in. The motor has some bolt ons like cam, long tubes, no egr, no air pump, no a/c. I had pcm for less tune the pcm. The car was idling pretty good from the get go but it would not kick down like it should when driving. The guy from pcm for less told be that the tps controls that and probably should change it. I changed the tps and now the idle is between 1500 and 2000. The car wont shift gears until it hits 4000rpm. If you leave off before 4000 the car acts like its in neutral until it hits the last rpm it was at before reengaging. The idle is now surging a couple of hundred rpm when in gear and in park. I changed everything back to original and it stays the same. It sounds like a vacuum leak but I didn't unplug anything. If anyone knows how to fix this please let me know. Thanks

Injuneer

Are the throttle blades fully closed at idle? You would need to pull the intake elbow and observe.

Sounds like the TPS is not letting the blades close. You need to measure the TPS voltage (key on/engine off) at closed throttle. Should be between 0.30 and 0.90 volts. Then rotate to wide open throttle and measure the voltage. Should be about 4 volts higher than the closed throttle reading..

Measure TPS voltage between the dark blue signal wire and the black ground wire. Alternatively, download a free copy of Scan9495 software and buy a 16-pin cable, and read the TPS voltage directly from the PCM. And, that software will allow you to log the PCM data while the engine and trans are misbehaving, allowing us to help you diagnose the problem.

https://www.camaroz28.com/forums/com...95-lt1-874306/

TPS wiring, courtesy of Shoebox

http://shbox.com/1/1995_pcm1.jpg

wildberryeagle

Thanks for the info. Hopefully the blades aren't closing like you said. I will **** with it tomorrow. It just sucks that changing the tps is causing so many problems.

wildberryeagle

Thanks Injuneer, that fixed my problem. The new one that I bought was no good, I had a few of them in the shed from previous problems and all but one was no good. I had to fiddle with the tps to get it to .83 at no throttle. The blades were open just a little bit so I adjusted the throttle stop screw. It took a few miles, but the transmission started to shift normal. Thanks again

Injuneer

Glad it worked out for you. Thanks for the feedback.