idle/tranny issues at startup

HELP i am having a problem with my 1990 plymouth gr voyager.when i start it up the check engine light comes on and it bucks and keeps downshifting the trany as i try to drive off.it give off a bad smell and keeps idling rough.after about 2 miles of driving like this it runs fine until it gets cold and the process starts again.i changed one speed sensor but couldn't find the next one.there is a sensor right by the speedometer cable .does anyone know what that sensor is??the haynes manual says its the distance sensor but the autopart store says there is no distance sensor.Please help anyone that can.

The first thing to do is get the computer code(s) that are setting off the check engine light and it will give you an idea where to look first.
To get the codes, turn the ignition switch three times (don't start the car) (on-off-on-off-on) and watch the check engine light. Count the flashes. In diagnostic mode, the computer repeatably flashes out each two digit fault code with each digit seperated by a pause. The end of the list is code 55. If you search the web, keywords "Chrysler computer codes" you will find a site which lists the meaning of each code.

thanx yogi...i got codes 12 15 24 41 ..i changed a sped sensor on the front of the tranny but i am still getting the speed sensor code..i see something called a distance sensor by the speedometer cable but the store tells me there is none there.so i am still at square one..and trying to find whats causing this problem.i really apppreciate any help at all that i can get.

The fault codes in the computer can be reset. The computer will remember fault codes for 50 or so ignition on sequences. To reset the fault codes in the computer, turn the ignition key on-off 50-55 times. The next diagnostic will set only those codes that are still a problem.

You may be having two problems here: The major problem is the 24 (throttle position sensor). This sensor is attached to the throttle plate arm and outputs voltage back to the computer that will translate into how open the plate is and how much gas to give the engine. A fully closed throttle is calibrated to output about .5 volts or so (not zero), and when fully open, about 4.5 volts. The code 24 says the voltage is going outside of this range. Either zero (loose wiring) or it's spiking high (usual case of a bad sensor). The computer is lost as to how much gas to give the engine and goes into a "limp" mode. It makes a guess. The bucking and downshifting are probably related to this.
The only thing about replacing this sensor is that care must be given to align it properly so that it is calibrated (to that .5 volts minimum). I've gotton around this by obtaining a replacement throttle body assembly at the junkyard (two bolts) just for the sensors. It's cheaper too - that sensor costs $50 new. It's getting too expensive to guess anymore.
As for your other codes: Ignore the 12 if you have disconnected the battery recently. If you have not, then it may relate to the 41 code (possible charging problem of some kind ). See if it is overcharging or undercharging.

hi i changed the throttle pos. sensor but i didn't really pay attention to calibrating it when i put it in..i thought i could just put it back correctly once the two bolts were aligned properly.i will check to see if the voltage is where my problem is..
also do you know what that sensor by the speedometer cable is?it says distance sensor in the hayns manual.the sensor i changed is one at the front of the tranny.
thanx for your responses ,you have really made this a fun experience to get another opinion.

plus i forgot to mention that after the engine warms up it runs fine ..no bucking ,idling problem or anything.i am really puzzled.

Hmmm? I only other sensor I can think of on the transmission is the neutral saftey switch, and I am unsure of if there are any other transmission sensors or where they are located.

If you only have a problem with the engine cold (i.e. No problem when vehicle doesn't move until the engine fully warmed up), then the problem is in the area of the engine, not the transmission.

The problem may not even be a sensor. Clogged throttle bodies are the usual cause of idle problems and can cause misfires at speed when they're really bad. Oily carbon build-ups occur (the PCV blowby) that clog air passages. The IAC (idle) is a moving valve (that can get stuck). You could try thouroughly cleaning out the inside of the throttle body using carberator cleaner. Both the main bore (past the big butterfly valve) and into the IDLE bore (the smaller 1/4 bore hole which is before the butterfly value on the inside side).