95 Grand Cherokee Rough Idle/Stalling

Greeting,

My HIGH mileage (220k) '95 Grand Cherokee (4.0L automatic) is occasionally idling rough and the rpm's will drop to a near stall just after coming to a stoplight, and sometimes stumble just as I'm taking off again. All of this is under normal driving conditions, no hard breaking or acceleration.

Otherwise the car runs great. Even when it's acting up as described, it's smooth and powerful above 1000 rpm. Recent new plugs, wires and fuel filter. Bad fuel is unlikely since this has been going on for a while and I buy gas from many different places I use premium. Everything else seems normal.

The injectors have not been serviced in a long time. Could they affect just the idle? I'll reiterate that the vehicle really runs great most of the time.

Thanks for any ideas, Tom

Reply to
tom_murphy
Loading thread data ...

Oh yeah, vacuum at the manifold is steady and within spec.

Reply to
tom_murphy

How does it respond when it is not completely warmed up; cold vs. warm. Jim

Reply to
gobroncos

Hi Jim,

It's maybe a little more frequent when cold, but happens when fully warmed up as well. I've been thinking it may be and oxygen sensor. I'd like to check the codes but it's pre OBD-II.

Tom

Reply to
tom_murphy

Hey Tom, If its acting up while cold, forget about replacing the O2 sensor. Engine management systems dont respond until O2 sensors are heated up enough to start putting out a voltage. This problem displays classic symptoms of a faulty EGR valve. Many auto parts stores provide free touble code scans. If there are no trouble codes present, I would start with a thorough primary electrical system check to at least eliminate that. Lets start with that. Do you have a digital multimeter? Must go to work now, and wont be able to respond until early A.M. Jim

Reply to
gobroncos

Hey Jim,

That's a good point. All of the auto parts stores around here (Dallas area) only have OBD-II scanners, and 1995 is pre OBD-II. The check engine light is not on. Yes I have a DMM.

I am actually a very experienced amatuer mechanic, but like many I'm a lousy diagnostician!!

I recently replaced the alternator which had failed in the traditional way - low output voltage.

Thanks! Tom

Reply to
tom_murphy

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.