1990 Dodge Spirit Rough Idling

JOEL222222

MEMBER
1990 DODGE SPIRIT

Engine Performance problem
1990 Dodge Spirit 4 cyl Front Wheel Drive Automatic 74K miles

My 1990 Dodge Spirit with 4 cyl engine has a rough idle issue. I took it to a local garage, which replaced the fuel filter, spark plugs, distributor pickup, MAP sensor. The problem persisited. I doscovered an easy trouble code diagnosis, which showed code 34, "an open of shorted condition detected in the speed control vacuum or vent solenoid circuits." Took the car back to garage, where the mechanic merely did something to raise the idle speed to about 1000rpm, which is higher than recommended 750 rpm. Problem seemed solved for a while, but the idle speed often dips below 1000 rpm, and it gets rough. It is very rough on a cold start. I checked the trouble code again, but got none (he probably cleared it when he raised idle speed). Any ideas?

3 Replies

MERLIN2021

MECHANIC
17,250 POSTS

You may have a vacuum leak, get a can of spray gumout, spray the vac lines and maniflod area, when the idle changes, youve found the leak! You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs! If that doesnt do it, you may need a new idle air control valve, it's bolted to the throttlebody