Engine fluctuating

[dpchai]

Hi everybody:

I have a 1991 Galant GSX all wheel drive with DOHC 2.0 engine.
Recently when I start the engine, the engine speed keeps fluctuating
between 2200 rpm and 1500 rpm (shift in Parking gear), then gradually
goes down to fluctuate between 1500 rpm and 1000 rpm. I changed the
air filter and pcv valve, checked the spark plug and spark plug
wires. I can not find out the problem. If anyone has the same
problem or know how to solve this, please let me know. Any
suggestion will be greatly appreciated.


Thanks


Deping

[bongi]

if it happens when the engine is cold, can be normal. if the engine is warm does it still make the same fluctuation? if not then it should be okay.

[BlueESV6]

I have a 92 GS 2.0 .... Mine suddenly stopped idling all together but would accelerate and drive fine (just would not idle but would die out). Anyway, there is something called an idle control motor that controls the idling... this might be bad.. pray its not... it's like $500-600! :shock:

Good Luck

[bongi]

try changing the fuel filter. idling control rarely misses, and it should have auto idling

[ken inn]

calm down. the idle speed control servo, MD628051(manual trans) list price is 257.03, if you go to www.mitsubishiparts.cc, you will see this part discounted, will cost only 195.86. and they do go bad. what you do is unbolt it from the throttle body, but leave it plugged in. then, have someone turn the ignition on, but do not start. when power is applied, the tip of the isc will cycle in and out, then stop. if it starts vibrating, it is no good.
but, you need to also consider the fiav(fast idle air valve) underneath the throttle body, which is fed by 2 coolant lines. if this goes bad, it is big bucks. also possibilities is an air leak, and a bad egr valve can leak and cause idle problems.
you need to start with the basics. set the base idle, on the vr4 there is a plug on the firewall you need to ground out, then using the biss(base idle set screw) set the idle to factory spec, on the vr4, it is 850 rpm. it is a good idea to also set base timing at the same time. the idle and the timing is controlled by the ecu, unless the car has a distributor, which i think the sohc and 16 valve cars do. on the dohc cars, timing is set by moving the cas(crank angle sensor), on the back of the cyl head, at the end of the intake cam. i suspect idle and timing(5 deg btdc) may be the same all of the engines.
remove the egr valve, and clean it with carb cleaner, and use a vacuum hose to check movement. instructions are in the service manual. also, if you have access to a logger, you can see your fuel trims, and o2 trims, and they can tell you if the car is running lean.