Mechanics

I TOLD YOU A FEW DAYS AGO ABOUT MY STALLING AT LIGHTS AND WHEN I PUT IT INTO GEAR.I HAVE READ ON ANOTHER FORUM YESTERDAY THAT IT COULD BE THE TRANSMISSION CONTROL MODULE.COULD THIS BE MY PROBLEM?AND IF SO HOW DO I FIND OUT WHICH TYPE OF TRANSMISSION

1998 Jeep Grand Cherokee • 11,200 miles

Car stalls at lights and stop signs and when put into gear
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Bobalou71
January 19, 2012.



Your message is cut off but it sounds like it could be the idle air control valve

ProAutoTech
Jan 19, 2012.
Sorry about that but I read on a forum recently that it could be the transmission control module. The jeep runs great idles great too. Only have the stalling problem at lights and when I put it in gear. Ive replaced IAC map sensor TPS tuned up changed neg battery cable and I cleaned the throttle body and checked the throttle body gasket which was in good shape. Still have the same problem though

Tiny
Bobalou71
Jan 19, 2012.
You caused the problem to remain by disconnecting the battery. The Engine Computer lost its memory and has to relearn "minimum throttle" before it will know when it must be in control of idle speed. Until then, you also usually won't get the nice idle flare-up to 1500 rpm for a couple of seconds when starting the engine.

To meet the conditions for the relearn to take place, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the pedals.

Caradiodoc
Jan 19, 2012.
Already did that

Tiny
Bobalou71
Jan 19, 2012.
Then you're going to need a scanner that displays live data to see what the computer is doing. The automatic idle speed motor will be shown with the "step" it is on from 0 to 256. 32 is typical for a properly-running engine. If you find it on a lower step, and the idle speed is too low, it hasn't relearned minimum throttle. One defective section in the brake light switch can prevent the relearn from taking place. If you find it's on a higher step, say 45 or more, the computer is trying to raise idle speed without success. An open circuit in any of the four wires going to it will be detected and set a diagnostic fault code. That will most likely not turn on the Check Engine light because it shouldn't have an adverse effect on emissions. The motor can not be tested accurately with an ohm meter because there are four coils of wire inside it all tied together. Two of them would have to be open to see that with an ohm meter, and it is very uncommon to even have one coil open.

Besides electrical problems, the air passage could be plugged with carbon or the shaft of the motor could be tight. Carbon was a big problem with the 3.0L engines in the early '90s, but we don't see that anymore with better additives in the fuel.

Two ways to see if the motor is tight are to remove it and see if the valve moves in and out when you turn on the ignition switch, or to use the scanner to perform the AIS control test. By pressing buttons on the scanner, the computer will run the engine speed up to 2000 rpm in 200 rpm increments.

You can also retract the pintle valve by hand when you have the motor out but it will be very hard to move. You'll have to use both hands to squeeze the valve in or pull it out. Once it has been retracted, you can install it that way and start the engine. Idle speed should be much too high but it will come down gradually as the computer pulses it to the desired position.

You can also try holding the brake pedal up with your toes when coasting to do the relearn. If that works, the switch could just be out-of-adjustment and road vibration is making one part of it turn on and off.

Caradiodoc
Jan 19, 2012.
I will try that I never pulled the brake up with my toes when I coasted

Tiny
Bobalou71
Jan 19, 2012.
If your vehicle has cruise control, it will have three switches built into the brake light switch. Two are off when the pedal is released. The one part that turns on is for the cruise control. I've had a few that caused the system to cancel while driving but low idle speed was never one of the accompanying complaints because minimum throttle was already learned and in memory. Holding the brake pedal up prevented some of those systems from kicking out over bumps so it stands to reason that same part of the switch could cause a failure to learn minimum throttle. The cruise control system is run by the Engine Computer and the brake light switch wires go to it.

I suppose a problem with the throttle position sensor could cause that too. When the computer sees high intake manifold vacuum for seven seconds or longer, it knows the vehicle has to be moving and coasting, and your foot is off the gas pedal. At that point it takes a voltage reading from the TPS. From then on, anytime it sees that same voltage, it knows your foot is off the pedal and it has to be in control of idle speed. If that voltage is bouncing around during the seven-second coast, the computer will assume your foot is still on the pedal and causing that change. I've never changed a TPS for that myself, but you might also check that the throttle cable has a little slack in it so engine vibration doesn't pull on it.

Caradiodoc
Jan 19, 2012.