Hello all I have a 96 blazer that has just had the engine replaced with a junker. Since I got the truck back I have replaced the idler pulley. The problem is when it is idling its almost like its giving itself a little gas at about 1 second intervals at the peak it is about 700-800 rpms and at its lowest it is about 450-500 rpms almost stalling. my idea is when my engine first died i had the cruise control on and couldnt get it off. I was wondering if it could be messed up. My first thought was to pull the fuse on the cruise control and see what happened but i couldnt find a cruise control fuse on the interior fuse block and i cant even find the fuse block itself under the hood . Does anybody have any ideas? thank you

 

It could be a EGR valve thats stuck open, thats known to cause a rough idle

 

Today I've noticed while it's idling the oil pressure is high. The more gas I give it the higher the pressure gets.

 

It sounds like a sticking IAC valve to me. Like it is sticking to a point then opens a bit. I would remove the throttle body and clean it up. Specifically the IAC valve and its bore which is located towards the back of the throttle body.

 

I had same type of idle problem and was lucky enough to have a similar engine vortex 4.3 and just replaced the iac valve and the other two components in the same area near the trottle body,sorry i don,t even know the names of the parts but you ,ll see em near the idle air control valve,one unpluges has a small harness and the other is on top of trottle body easy to replace all of em,sorry i can,t be more help,but this may point you in the general direction,and it really fixed my problem,it starts right up and runs really smooth,good luck,jim

 

Your common culprits to idle problems are IAC, a/c, TPS, EGR, and a vacuum leak. Since the engine has been switched, make sure the vacuum hoses are all connected and you dont have any leaks. Best way to listen for leaks is with another piece of hose. Place one end up to your ear, and move the other end around the engine compartment, your listening for a sucking or whoosing sound.