Subject: 1992 MIT. GALANT ,ENGINE SURGING
Question: MR FALCONE,
I HAVE A 1992 GALANT LIMITED EDITION 4 CYLINDER TURBO,I HAVE PROBLEMS WITH ENGINE SURGING AT IDLE SPEED DURING COLD WEATHER AFTER ENGINE WARMS UP.IAC AND FAST IDLE VALVE REPLACED, COMPUTER CHIP REPLACED LAST FEBRUARY. NOW SAME PROBLEM BACK THIS YEAR WITH RETURN OF COLD WEATHER.WOULD APPRECIATE ANY IDEA'S BEFORE I RETURN IT TO REPAIR SHOP. THANK YOU.
LARRY STEWART
Answer: Larry,

The older Mitsubishi turbo engine (4G63) does have a problem with cold idle surging. When I would start my turbo Eclipse from a cold start the car would idle at around 2500 - 3000 RPMs for the a minute or so.

It's supposed to idle between 700-800 RPMs (manual transmission) when the engine reaches normal operating temerpature. Lower RPMs for automatic trannies. Your idle surge could be do to any or all of the following:
-Base Idle Set Screw
-Thottle Position Sensor
-Sticky thottle plate
-leaking vacuum hose
-incorrect grade of engine oil
-incorrect ignition timing

When you had the other items replace, it may have been performed when the engine was cold. Your mechanic needs to make sure to your engine has reached normal operating temperature before making idle settings. There are sensor cables that need to be grounded and when setting idle speed as well. Most mechanics won't do this, but its vital for getting the correct idle speed. Call your local Mitsubishi dealership and ask for an estimate to just set the idle. If its less than $80 USD, bring it to them. They'll do it right.. once and for all.
Good luck!