have a 99 blazer and more often than not it will surge a few hundred rpm then go back to where it was.does it more with cruise control on but does it without also. sometimes it surges as much as 5 or 6 hundred rpm then drops back to where it was.any help will be appreciated..thanks..Dave

 

This could be caused by quite a few different things.
Throttle vane sticking,
Idle air control valve sticking,
Throttle position sensor issues,
Mass Air Flow sensor issues,


I would suggest trying to rent/borrow a scanner that can read real time data from the above sensors. This way you can see what they are doing when this issue happens.


I am not sure if this will help but I had an issue sort of like this with mine when I bought it. Mine is a 5 speed manual and would rev up between shifts and rev up when put into neutral occasionally but it was very intermittent.
Mine was due to a bad Throttle Position Sensor.


I had to put my scanner on it and read the sensors while I was driving because it was intermittent. My trucks TPS value would usually drop to 0 like it should but sometimes I would let off the throttle to shift and the TPS would hang at 24%. This caused the ECM to think the throttle was open and feed it fuel causing the engine to rev up.


I hope this helps. I am just trying to give you an idea of some stuff to check.

 

thank you for your sugestions you have been very helpful. Dave..