Hi Idle Transmission, Cpu, Iac or WHAT!

Ok I saw the post on the kick down by Indamiddle77. I read it and I am some what confused on the directions since one guy was talking about a Mopar trans but INDA had a AW4. I also read the post by Tayln regarding kick down adjustment for an AW4. So if that can be clarified for me to do IF that is my issue! I have a 1000 to 1200 rpm idle problem which is causing poor fuel mileage and cruise control like effects while driving.

Here is the back ground:
1999 2wd Sport 4dr auto AW4 4.0 233K.
May be irrelevant, but Prior to Trans starting to slip, I adjusted the selector cable on the pass. side of trans because it was between gears on the console. I messed with the little 1/4 round thing with the nut that is adjustable!
AW4 was replaced with a used one. It had about 100K on donor trans with *NO CODES* after installation.
I had Hi idle before trans swap. Had a TPS code before trans swap but cleared it and tested TPS. TPS tested good.
New trans shifts great I do need to remove some fluid it is about 1/4" above fill mark on dip stick. (Irrelevant?)
I still had hi idle after swap. Thinking it is still IAC problem, I pulled throttle body off and cleaned thoroughly every component of the T. B. I Installed but it made no changes .
I purchased a used T.B. cleaned it and installed it and it ran better but hi idle came back after a day or maybe same day. The days and results are starting to blend in!

Here's where it gets goofy; at start on a cold engine runs great, idle is about 800, 900. After a few minutes and it warms up 'IF' the idle comes up it only comes up to about 1000. When I drive it and come to a full and complete stop, and only if I come to a complete stop, within a second the rpm's will drop to 800-900 and idle perfect. If and when I remove my foot off the brake, without throttle application, it will roll and jump back up to 1000-1200 rpm's once the vehicle is moving.
After it has run around town the hi idle 1200 is there and if I shut it off and restart the vehicle while still warm right away or 10 minutes or so later, the idle has gone to 2000+ and slowly drops within 3-5 seconds.

Questions:
Is this a computer problem since it started doing it off and on prior to the donor trans?
Is this a kick down cable problem? This is the second donor trans the factory trans went out about 195K, this one was put in at 233K!
Is this a brake pedal transmission switch problem? I've read there is a switch for the converter on the break pedal!

I would suggest, that you make sure the throttle is closing completely. If you adjusted your throttle cable, do you think there is a chance that it is not allowing the throttle to close completely ? Even if it's hanging up just a little bit, it could cause the idle issues you are describing. The ecu only try's to idle the motor when it believes the throttle is completely closed. Also, you could have an issue with the throttle position sensor.

Closed throttle position is learned, learning process :

Every key on, ecu bumps minimum closed throttle voltage by .04 (usually) volts, so lets say your closed throttle voltage is .76 volts, shut down Jeep. Re-key on, minimum voltage moves to .80 volts, you crank the engine, engine starts, actual throttle voltage is .76, ecu then learns down to .76 volts. Keep in mind that the ecu only learns down, not up, it increments up at key on. If you sit there and key off-on, off-on ..... it will keep bumping minimum throttle volts to about 1.2 (this varies slightly on the calibration), but one the engine starts, it will adjust down to the lowest throttle voltage, in this case .76 volts. Now, the ecu will recognize the throttle as being "open" when the voltage increases by .02 - .04 (again depending the particular calibration) above the stored minimum of .76 volts. So assuming .02, when your throttle moves above .78 volts the ecu is no longer trying to control idle speed, instead it goes to a different set of routines for off-idle IAC control.

If you don't have access to a scan tool, get a digital volt meter, and wire it to the throttle position sensor signal and signal ground at the ecu.

Signal C1 (black) pin 23
Signal ground C1 (black) pin 4

Sorry if I miss lead you butt I did not adjust throttle cable just shifter cable and the crescent moon shaped module bolted to the side of the trans with the 4-6 wire harness. Thanks will try as soon as she gets car home. I do not know if you caught the part about replacing the T.B. all the sensors that came with that T.B. were used. My old T.B. has the originals. I will also disconnect batt for a day and let the cpu reset. I will check kick down and throttle cable ease of travel. One thing I forgot to mention is I also checked for vacuum leaks with carb clnr and either but could not find any.

Hard to believe that the new T.B. TPS may still be bad even though it is not the same one? You do raise the question though, as to possibly a bad TPS connector, melted or frayed wire! I'll have to check! Any thing on the brake pedal switch or kick down cable or the crescent moon switch?

Genuine Jeep TPS, of some crappy Chinese "Lifetime Warranty" junk ? Cheap parts are cheap for a reason, and often are poorly constructed, out of tolerance, or even failed before they ever leave the store. Many threads detail long, frustrating, and expensive searches trying to pin down an issue that was easily solved with a genuine Jeep sensor.

Boss Cherokee said:

Here's where it gets goofy; at start on a cold engine runs great, idle is about 800, 900. After a few minutes and it warms up 'IF' the idle comes up it only comes up to about 1000. When I drive it and come to a full and complete stop, and only if I come to a complete stop, within a second the rpm's will drop to 800-900 and idle perfect. If and when I remove my foot off the brake, without throttle application, it will roll and jump back up to 1000-1200 rpm's once the vehicle is moving.
After it has run around town the hi idle 1200 is there and if I shut it off and restart the vehicle while still warm right away or 10 minutes or so later, the idle has gone to 2000+ and slowly drops within 3-5 seconds.

Click to expand...

High idle commonly associated with vacuum leak. I would also check around the break booster for a vacuum leak since you say it gets better when brake booster is in use. Long shot, worth a look see anyways.

If the engine runs normal cold but idles high when warm, I'd check the intake manifold bolts for a vacuum leak with ether as well. I don't know jack, but I threw money at a high idle problem and all it needed was a bolt tightened. I watched my mechanic spray the ether and listened to the idle increase. I just shook my head.

Be careful with that high idle too. Stopping on loose gravel or in mud can be sketchy when the idle is high. Your front brakes will lock up while the rear tires keep pushing you.

Be careful with that high idle too. Stopping on loose gravel or in mud can be sketchy when the idle is high. Your front brakes will lock up while the rear tires keep pushing you.

Roger that my driveway is 3/8 to 1/2 loose gravel. Already experienced it!

Do a "minimum air flow test", pull the intake boot and plug the idle air passage with your finger, if it dies or barely idles your problem is likely not air leak related.

Thanks will do!