rpm is jumping

[pvtz]

what would be causing the motor in my 87 4 runner to not stay at an rpm, like for example when I went to do my emissions test I couldn't because my truck won't stay at 2500 rpm, it jumps around and I can't figure out why!!

 

[kowe69]

what would be causing the motor in my 87 4 runner to not stay at an rpm, like for example when I went to do my emissions test I couldn't because my truck won't stay at 2500 rpm, it jumps around and I can't figure out why!!

Usually that's caused by them running the test with the A/C on. The compressor turns on and off and loads and unloads the engine. Making it very difficult to maintain speed on the dyno and/or engine rpm.

 

[Lifelong Jeeper]

What about throttle position sensor or cam shaft position sensor needing replacement. If they aren't working then the computer will be trying to regulate the engine inappropriately.

???

 

[78mitsu]

could also be cracked and bleeding EGR diaphragm.