Mitsubishi Repair: 98 diamante rough idle, crankcase pressure, torque requirements

Question
I have a 98 Diamante with a 3.5 liter automatic. The car has 105K miles. It has had regular maintenance. I paid the dealer to change the Timing belt, plugs, wires about 30K ago. The car has a rough idle. You can hear it sputter at the exhaust outlet. I cleaned the IAC motor (it revs when compressor comes on) The dealer just cleaned the injectors. Any thoughts?

Answer
MArk,
A rough idle can be difficult to diagnose; even for the dealership.  A quick fix could simply be to replace your PCV valve. A little valve that releases excess crankcase pressure. Very inexpensive and easy to replace.

Other areas to check are your fuel and ignition systems. Have your fuel pump checked and your fuel filter replaced. A clogged fuel filter will reduce the amount of fuel entering your engine and cause poor idling and possible stalling. Your ignition system is basically made up of your alternator, distributor, spark plugs and spark plug wires. You'll want those items inspected and replaced if necessary. You spark plugs and plug wires should regularly be replaced every 30,000 miles or so.

The last thing I can think of to have checked is your transmission. Your torque converter kind of acts like a clutch as in a manual transmission vehicle. If your torque converter is not changing the torque requirements when your car is stopped, then your RPMs will quickly drop down, and the car will idle poorly. Next time you're at a light or stop sign, and you feel you're going to stall, move your shifter to N (neutral) and see if that brings the life back into your car. If it does, have your mechanic focus on our transmission and your ignition timing. Also have your transmission fluid checked and replaced if low or dirty. It should be flushed and replaced ever 30k-40k miles.

As you can see, diagnosing a rough idle problem is not easy. There can be several causes, and every mechanic and person with some knowledge of cars (like me) might have different views on areas to check. Next mechanic you bring your car to, give them the list of items I've recommended to have checked, and then you'll know what worked or what can be ruled out.
Good luck!