Mitsubishi Repair: 92 2.0 SOHC Galant IDLE GOING CRAZY, galant sohc, merry xmas

Question
Hi sir,

I'm in dire need of help as my 2.0 1992 Galant SOHC A/T has started going nuts on me. I have new sparkplugs, changed oil, changed ATF oil, normal tune-up stuff, the works, but i still have the problem - the problem is: when i start my car in the morning (cold), the rpm's seems like they were possessed, it goes from 1000 - 2000 and vice versa, like someone was stepping on the gas.  Turning on the AC lowers the idle speed a bit, but it still seesaws from 800-1700 rpm. Reving the engine to 3000+rpm and letting the pedal go doesn't help.

When the engine warms up to the normal temp, the seesawing disappears, but another prob is happens (might be related). The car is automatic so when it's in neutral or park, the rpm is at a nice 850rpm (with the AC on), but once I shift it into Drive or reverse or any other gear, the rpm drops to around 650-700 rpm and causes the car to vibrate. With the AC off, the rpm is around 950rpm in neutral or park, in drive or any other gear, it's around 850rpm.

I've had the Idle Air Control (IAC) checked, the mechanic said it was working normally because he hooked it up directly to the battery and the solenoid? was moving ok. Please help as I need this car daily to drive to work :(

Thanks in advance to all.

Kind regards, and Merry Xmas to all,

Shaun

Answer
Shaun,
Your problem is commonly referred to as Idle Surge, and can be a problem for any car.  The engine used in the early model Galant is pretty similar to the Eclipse engine.  There is a site which explains how to test the IAC yourself (also referred to as the Idle Speed Controller - ISC).  You can examine the procedure here:
http://dmtalon.v8eaters.com/ISC.html

Your mechanic did the right thing by seeing if the solenoid (basically just a plunger) was moving, but that does not necessary mean your IAC is ok.  There are several coils in your IAC that need to be checked.  The solenoid itself may still be faulty.  Just because it moves does not guarantee it's making a good seal.

Check your IAC again, or bring these instructions to your mechanic and have him check them.
Good luck!