Rough idle when cold

My friend has Plymouth Voyager 1995 w/ 3.0 motor. he is concern with rough idle when starts in morning. He took it to dealer shop 6 months ago. they tested & diagnosed it was the A.I.S. Engine acting up inermittenly.or rough idling when cold.When the engine is warm up it run smooth. dealer replace something and it works ok. but now the problem is back again.The same as it was 6 months ago. if he will take it back to the dealership he will be charge or replace that thing again and cost another 100 bucks. Any comments is highly appreciated Thanks

First see if the computer has any problem codes stored in it. This usually leads to the fault censor/circuit. The Check Engine Light will come on when there are problem codes present.

Chysler computer codes (80-95 Chysler's):

To obtain codes: Turning the ignition key on-off-on three times (don't start the engine) will put the
computer into diagnostic mode. Watch the "check engine" light. Count the flashes for each digit which is followed by a pause between digits. Two digits to a code with the end ofthe list being code 55.

Codes other than 55 are problem codes. Some are just informational. Use the following link to get the meaning for each code.

http://www.allpar.com/fix/80s-codes.html

If a diagnostic code is present, your problematic idle is probably related to that.
If you have no diagnostic codes, the 3.0L engine can also have poor idle/misfires when water from condensation gets into the gas (use a drygas product) or when the ignition system hasn't been tuned up for a while. Tuning up the car means changing the plugs, the distributor cap and the rotor. A new set of wires is optional.

By the way, the A.I.S. you mentioned is the air idle sensor on the throttle body. The computer controls the idle by sending signals to it causing movement to a small valve regulating the air going into the engine so as to control idle. If there is oily buildup (it tends to get grungy in there from the pvc valve over time), then the valve in the I.A.S. can stick causing poor/eratic idle and occational misfires. The solution in this case is to liberally spray carberator cleaner into the air intake of the throttle body past the butterfly valve. It will surprise you what crud comes out. The idle intake is a small air bypass bore hole in the side of the main air intake, so be sure to clean that too.