Idling high, but IAC at zero implies a vacuum leak somewhere. Question becomes, where??? Is the plenum gasket blown??

 

IAC is zeroed because I had opened the throttle stop a little so it would run long enough to go to closed loop when I was checking the O2 sensors. IAC was running around 30-35 before that. It absolutely does not have a blown plenum or vacuum leak. I've gone through all that a dozen times. Even pulled the intake and resealed it all, again. Here is a log of it with the idle screw back down to normal. It'll only run for a few seconds like this. Idle surge

 

Try disabling MAP, and TPS, (one at a time) and see if idle will stabilize.

 

TPS unplugged it stays runnning a little longer but still surges badly.
MAP unplugged it starts and dies immediately. If I start it and then unplug the MAP it stays running but still surges.

Top is MAP unplugged, bottom tps unplugged

 

So those are probably ok then. I am rapidly running out of ideas....... We have eliminated everything I can think of. I am just not sure what else it could be.

Just curious, but, what plugs do you have in there?

 

If the MAP is unplugged why does it keep reading? Does it go to baseline instead of 0?

 

I'm not sure but I'm guessing its showing the default value that the computer is using. It does show as MAP Fault limp mode.

 

What's the history on this motor? what year, matching PCM?

 

I bought it as running and driving 99 durango with 141k on it. Pulled engine and trans. Resealed front cover, oil pan and rear main. Pulled the heads, cylinders looked good but heads were cracked between the valves. Put back together with reman heads, replaced plenum plate with aluminum off ebay and new grade 8 bolts. Sent the pcm from the durango to a guy in Utah who removed the Skim because the jeep doesn't have any security stuff. Harness is built out of a combination of a tj harness and a ram harness and matches pin for pin all the stuff on the durango harness for engine and trans input and output. I got a second pcm from a 2000 ram and it runs the same with it. I'm using a gps speed sensor instead of getting speed signal from the abs module, and the speedo works with it. I don't think that would be the issue though with it idling in park.

 

It currently has NGK nickel plugs. I had champion copper plugs in it when I first started it but I swapped these in after a week or so of troubleshooting this idle issue. Has new cap and rotor also.