Installed modified Kegger, 180 Tstat, SCT Tune, Double Roller TIming Set, new water pump, polished TB, and CAI. Cranked up and runs great.

But idle is at 980 - 990 rpm. IAC changes from 0 to 1 step. I did a search and checked Haynes and FSM and cannot find an answer. I need to slow idle down about 250 to 300 rpm. Don't see an adjustment on throttle cable. Anyone know what I am missing?

Thanks.

 

I would say that the pcm is still learning, how long has it been run for?

 

Less than an hour. Long enough to flush radiator (had dirty coolant) and drain and burp system a second time, and only a short drive in town.

Does it take a while to learn? If so, I'll give it tomorrow to see if it comes back to normal. I can connect my MTG 2500 and idle up and down with it. That is how I know what IAC is doing while it is running.

 

Here are my thoughts in no particular order.

0. Is the truck warmed up?

1. You said you installed a polished throttle body. Did you do this / where did it come from? If the set screw has been messed with, you might have to tweak.

2. SCT tune installed, does it still high idle without SCT?

3. Vac leak

 

From my experience, it takes about 100k for the pcm to relearn itself. Are the TB cables binding on anything? Did you disconnect the neg cable while you were working on it?

 

Polished TB myself. Will look at it tomorrow, but I think all is good with it.
Battery was disconnected for the last week while I was working on this.
Throttle cable is not binding. Seemed to idle fast before loading tune as well, but not 100% certain.
I double checked all vacuum ports and hoses.

100k for PCM to relearn itself? Is there a typo here? Seems pretty long.

 

i would expect the pcm to immediately adjust iac to achieve the proper idle speed, based on its readings of engine temp and rpm.

if its not doing that, then either the iac is not responding, or you may have a vacuum leak causing the high idle.

having the battery disconnected and resetting the pcm should cause it to reset to the default settings which should be pretty close to cold idle of 1000 rpm and warm idle of about 600.

i think something's wrong, but give it a day or two just to give it that slim chance of fixing itself.
also - TPS can malfunction and create fast or surging idle. tps can override the idle function, if it thinks you have your foot in the gas.
also as said - tb cables misadjusted can pull the plate open and override idle function.

 

TPS checks good, and with MTG 2500, shows to be at minimum voltage during idle with no change. I can increase rpm with MTG and TPS follows correctly.

I will check again for vacuum leak, but cruise, heater/AC, power brakes, and other vacuum related functions work well. Replaced PCV (Mopar part) and both vacuum lines to valve covers with new hoses.

Only adjustment on anything throttle that I could see was throttle valve to transmission. Don't see any adjustment on throttle cable, but I may be overlooking it. I will look down TB and see if plate is open or closed while idling tonight. This is a different TB than what I had on it. It came on the JY intake that I modified. I may put original TB back on if I cannot find the problem.

I am wondering if IAC is resetting to what it thinks is closed position (possibly binding before it gets to close) and then steps back to 1 for idle, which may in fact be too far open. I may put the other one in and see if problem persists. Gas is too high to idle this fast!

 

swap IAC motors, see what happens. Don't forget to reset the pcm afterwards.

 

Will resetting PCM default to SCT tune, or orignial factory tune?