Ok i just did a valve job on my 1994 22re because the #1 intake valve somehow got slightly bent. new felpro gaskets everywhere. start it up and runs great but then start to notice the idle is kinda raising. it continues to raise until about 2000 rpm and then it start to surge down to 800 back to 2000 quickly. and just continues to do so. when you rev it revs quick no lag. seems to run great other than that. i have checked and rechecked all vacuum hose routings and i am positive they are correct. has new plugs, cap and rotor and does not seem to be a miss fire problem. thought the egr might be stuck open so i applied vacuum to it and it really starts missing. if i adjust timing it seems to slow down the surges but does not eliminate. has 150 psi compression across the cylinders. if i pull the oil fill it seems to almost stop the surging temporarily. i am stumped. when i got it was missing on cylinder 1 so no way to tell how long it has been doing it. when i pull one plug wire the miss starts and surging stops. anyone know what might be wrong???? please help trying to go wheeling need it to run right. thanks

 

check out the throttle position sensor:
http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml
there is a circuit in it that tells the ECU that the throttle is closed, and if it's not reading properly, engine speed fluctuations can occur.
as well, vacuum leaks can cause this situation and the ECU's coolant temp sensor.

 

Is this with the AC on? Does it stop when you turn the AC button off?

 

Mine does the same thing. Easy check is to just unplug the sensor. Mine stopped surging when I did this but also idles higher. Apparently they rebuild these things , so I figured I may just pull it off and try to clean it up a little.

 

ok i figured it out and i will admit my stupidness. i have always been a GM car guy actually have GM training. When i was doing the head gasket i noticed the 2 coolant lines going into the Throttle Body. On most GM cars this is an emissions control that warms up the TB to make the fuel less dense therefor less fuel. so thinking i would add a little performance i bypassed them. Come to find out that is their genius way of sensing engine temp for the idle hence the strange problem. Reran lines and all problems solved. So it was my doing not the truck.