I am working on a 1989 Cherokee 4.0L Automatic... High idle problem... I have tried 3 different IAC's and none seem to be closing. I cleaned and tried two different throttle bodies. I replaced the TPS, New base gasket. Adjusted throttle plate opening. Checked for vacuum leaks. Now here's the kicker... if I block off about 95-99% of the air opening on the top of the throttle body hole that is regulated by the IAC... it will idle just fine. I did find a splice on one of the wires to the plug for the IAC. It is soldered and looks good.It is blue with a yellow stipe. I put a test meter and got around 6.4 volts. So now I have disconnected the negative terminal on the battery and am going to see if that makes a difference. Does anyone have a possible solution? By the way the ground at the dipstick looks good... Is the IAC only controlled by the ECU? Sorry for the long post... I am stumped...

 

Cruiser54 will chime in. Any "Renix" issue is right up his alley......stay tuned.

 

It's getting air from somewhere else besides the throttle body then.

Have you checked to see if your intake manifold bolts aren't loose?

 

Checked the intake bolts and found several loose. Have tighten those and the problem still there. I blocked off all vacuum lines and fittings and removed throttle body. Did a smoke test on intake to check for vacuum leaks. The only smoke I am getting is from the bottom of the EGR valve that connects to the intake. Could this be a possible problem causing the high idle? Drawing O2 into the intake?

 

Absolutely.

 

So I removed the EGR valve and plugged the opening on the top hole. My idle dropped to 900 rpms. But I am getting a lot of exhaust gases coming from the bottom hole where the tube inlet is. Is this normal? Seems like a large amount. What would happen if I capped that line off? Going to try a different EGR valve and see if that solves my vacuum problem. Any other idea's?

 

Leave the EGR on there and plug the intake manifold and exhaust manifold bungs.