I purchased and used the Mopar combustion chmbr clnr as described, but no change in the surging idle.
If the car sits overnight or cools off, when first started, it runs normal, idle that is. Normal high idle while cold, but when it reaches temp, it starts this surging. I cant find any vacuem leaks but using a hose as stethoscope, I can hear a hissing between 1&2 just above the exhaust manifold. I didnt try to hear this sound while the engine was cold. Will try.
Ray l
Vehicle: 1990 - 1994 Mitsubishi Eclipse 2.0L
Symptom: The idle surges up and down when the engine has reached partial warm-up temperature.
System: Emissions/PCM/Fuel
Codes: N/A
Problem: Idle air control (IAC) is stuck in open position. Speed is high enough to cause the powertrain control module (PCM) to go to fuel cut.
Test & Fix: Either the idle air control (IAC) has an open winding or it is stuck. Remove the air intake duct and put duct tape over the air by-pass opening to the IAC. Install the air intake duct and start the engine. If the idle is back down to normal, check the resistance of the 4 windings in the IAC. To check resistance of the 4 windings, unplug the 6-way connector from the IAC. Consider the 6-way connector as 2 rows of 3 cavities. Connect one ohmmeter lead to one of the center pins in a row of 3 cavities. To check the first winding, connect the other lead to a pin on either side of that center pin. Normal resistance is 29-35 ohms at ambient temperature. To check the second winding move the outer lead to the pin on the opposite side of the center pin that is connected to the ohmmeter. To check the third and fourth winding check the other row of 3 in the same way. Replace the IAC if any of the windings are not 29-35 ohms.
see if this helps, on some of the older ones the IAC would go bad and take out the computer or the computer would go bad and take out the IAC, and those late eighty / early ninties Mitsu computers were spendy and went out often
Vehicle: 1990 - 1994 Mitsubishi Eclipse 2.0L
Symptom: Vehicle has incorrect idle speed. Base idle adjustment procedure.
System: Emissions/PCM/Fuel
Codes: N/A
Problem: Incorrect base idle speed.
Test & Fix: Clean the throttle body. Bring the engine up to operating temperature. Check and be sure the base timing is set correctly. Shut off the engine. Ground the set timing connector. Also ground pin #10 in the diagnostic connector. Start the engine and check the idle engine speed. It should be 750 RPM, + or - 50 RPM on non turbo engines and 800 RPM, + or - 50 RPM on turbo engines. If not, adjust as necessary using the adjustment screw located on the top of the throttle body. It is usually covered with a rubber plug. Remove the plug to adjust, then reinstall it when finished. Shut off the engine and remove the jumper wires. Base idle speed is now set.
here is another thats not quite as close but maybe relivant
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