My 91 has an idle issue. It won't idle at a consistant rpm it surges but not all the time and doesn't matter what the engine temp is. already changed O2 sensor, air and fuel filters.

 

you probly have a vacuum leak.

 

Thought of that too but my experience with vacuum leaks is a constant high idle not a surging idle.

 

What happens when you step on the brakes while parked and idling (warm engine)?

 

air leak behind the VAFM is possible.
timing should be at OEM (engnbldr told me 7* is optimum for the ECU)
i'd make sure the vacuum lines are all good... and that pipe from the VAFM to the Throttle body.

do you have a good chain?

 

revs normally when i hit the gas and settles back to idle then resumes surging, warm or cold
it surges like you are lightly tapping the gas pedal

 

Check engine light on? If so pull the codes by jumping TE1 and E1 in the diagnostics box...

I'm leaning towards your IAC. It's either bad or clogged up. Here is a simple test to find out...

1. Remove air intake tube at the throttle body. With a piece of duct tape cover the large hole on the bottom of the throttle body right in front of the throttle plate.
2. Reinstall the air intake tube and start the truck. If the idle returns to normal then the IAC is bad or clogged up.

*Do not rev the motor too hard, so it doesn't suck in the duct tape*

Give it a go and let us know what you find...

 

carb cleaner or w/e intake cleaner helps alot

 

clean ur throttle body and MAF (mass air flow sensor) make sure your air filters clean.