This occurs sparatically, although more often than not. It's really strange, and I can't think of anything that would be causing it. OK, the best way to describe this is in a scenario, so here it goes:
I'll be driving around with the car and everything at full operating temperature (or warmed up, basically). Let's say I am cruising down doing 40 or 45 in 4th gear, and I am coming up on a red light. I push the clutch in, RPMs drop right to 1000. I shift into neutral, the RPMs stay at a constant 1000 (clutch still in, idling). I come to a stop at the light, and shift into first gear to get ready for the light to turn green. When I shift into first, the RPMs go up and down, from ~1100 to 1000. Now I have something loose and rattling under my car by the catalytic converter, so everytime it drops from 1100 to 1000, the thing rattles - very annoying. Anyway, if I shift back into neutral, the RPMs stable out again at 1000. The weirdest thing is that it doesn't happen all the time. Sometimes, I'll put it in first and it'll rev up to like 1300 and drop off (causing the rattle again). Sometimes, after I take it out of gear the first time and put it into neutral, it'll rev to anywhere from 1100 to 1500 RPMs and stay there for a little bit, then drop off to 1000 (until I put it in first again, then usually it does the jumping thing.) What the hell is wrong with my car now? Any suggestions? I am not throwing any CEL codes, so I don't think it's a bad sensor. I don't understand, but it's really embarrassing to be sitting there with the thing revving and rattling...not to mention annoying as hell. Please help me,
Tyler

 

Unplug the 1st-2nd switch on the transmission and see if that helps .

 

OK, thanks -
I don't know where that is, though? Could someone tell me where this switch is located, and maybe what it does?

 

Anyone?

Now it seems as though it only happens during the day...so maybe only when it's warmer out? I drove it home tonight, and it didn't fluctuate at all. I also got a better boost pattern than during the day. This is crazy.

 

I HAD THE SAME PROBLEM ON MINE. EVEN AFTER I PUT A NEW ENGINE IN, THE SAME PROBLEM WAS THERE. A NEW PROGRAMABLE ECU SOLVED IT. I FOUND DURING THE ENGINE SWAP THAT I HAD A light flywheel. MAYBE THE STOCK COMPUTER CANT KEEP UP.

 

I have that problem on my car itll bounce the rpms up and down and sometimes they will fall to like 100 and i mean 100. But the ecu is the problem I hear and so that means power fc.