Erratic RPM's

[MikeWild]

I'm stumped, I just completed a 2.9 to 4.0L swap into my 91 5spd ranger. Everything seemed to work fine once I fired it up and did a test drive with it yesterday. This morning, I drove about 10 blocks to the store, everything was fine. Coming home, it all went south. Here's the symptoms:

Starts fine
Idles fine

As soon as I go to give it gas, the RPM's jump up and down like I'm pumping the throttle. I thought it might be the IAC valve, so I unplugged it and it just stalled out. I thought maybe there was a ground wire issue as my negative cable looks like poo so I cleaned it all up. No effect. Checked the ground wires at the ECM, and they look fine. Tonight I went and played around a bit more, checked the vacuum lines, MAF, all look good. I don't suspect a faulty fuel pump or filter as the truck drove fine with the 2.9 prior to pulling it. I also don't suspect the 4.0ECM as I also drove it without issue prior to yanking the 4.0. Out of 10 fires, it ran and revved perfectly as though nothing was wrong one time after completely shutting the truck off, then it went back to messing with me.

I've read that the ABS might be connected in searching similar issues, (my ABS is not hooked up, but it was like that and drove fine with the 2.9) so I doubt that's relevant.

I'm suspecting a possible TPS issue, but would appreciate any insight you all might have in solving this issue.

 

[MikeWild]

I noticed today when farting around with it, that as soon as I brought the RPM's up to around 2000 is when it started it's revving up and down routine, but if I kept it under 2000, I could shift through all the gears and get the truck somewhat up to speed.

again.... any suggestions would be appreciated.

 

[MikeWild]

finally figured it out today. Turns out it was the CPS