camoken63

'97 GCL, high mileage but serviced regularly. Began having random incidence of suddenly dropping rpms, engine would almost die if you left your foot on the gas. Let up for a second and it would clean right up. Then began to actually die. Would always start right back up and run normally. Occasionally would take several attempts to re-start but it would re-start. Replaced crank position sensor, coil, wires, plugs, magnetic pick-up in distributor. no luck. Jeep said it was PCM. Replaced it and ran good for a couple weeks then same old thing. Not a fuel problem, rail has correct pressure before and after starting. Sometimes after dieing I turn the key and .... nothing at all. Wiggle the shift lever or start in nuetral and it starts, but usually it does crank. Runs great except when it dies. Noticed I can make the engine skip by wiggling the middle connector at the PCM. Inspected both interfaces and they look clean and no burns or bends. Seems like the problem clears up for a few days after I disconnect the PCM and battery, but then comes back. Don't want to have to buy my wife another vehicle, she loves her Jeep and it is in excellent shape but I'm out of ideas, please help.

Bustedknuckle

Check the harness. I've seen ZJ's before that'll cut out. Some were the MAP sensor, others were a loose wiring harness near the exhaust manifold, comes loose, exhaust burns through it to the wires, then shorts them out, blowing the ASD fuse.

camoken63

If the ASD fuse was blown it wouldn't start or run at all, right? Have checked the entire harness and it looks good. MAP sensor would throw a code or check engine light wouldn't it?

robbob

I had all of the same symptoms u do.I replaced all the same parts.so I pull the three pin connectors from pcm and put some dielectric grease on pins,I really layer it on thick.now problem gone.runs great.

Bustedback

Sounds like the IAC motor is starting to fail. NAPA will have it for around 55 bucks.

Chad149

My 93 was doing that as well. My cheap *** took the IAC motor off and cleaned it. Been fine so far, but is an off road toy that sees limited road use. Had 140k street miles before that occured.

camoken63

Thanks for the tips Jeepers, I have cleaned the PCM connectors with contact cleaner and greased them up with dialectric grease. Wife is driving it right now.....fingers crossed. What is the IAC motor? Sorry to be dense but I don't recognize the letters, thanks again!

freegdr

iac motor, idle air control on throttle body

Phatwitaph

something to keep in mind, 02 sensors can make a vehicle do wierd things, mine would stall and wouldnt go anywhere no matter how hard i mashed the gas, turn out to be the 02 sensor after the manifold.

Traction120

Same thing here. Bought by jeep a week ago, cleaned out throttle body and iac, and it ran fine until today, I'm going to buy a new iac tomorrow, then I'll get back at this thread..

camoken63

Thanks for the info, I'll check that out if the trouble continues..... I think O2 sensors would trip the check engine light though. Wouldn't the idle air control motor do the same?

Chad149

The check engine light will come on only if the ECM sees something electrically wrong-more of less outside of set parameters. IAC motors tend to gum up over the years and far as the ECM can tell all is well but in reality the motor/valve is stuck.

cjseipp

Plagued with the same issue and also can manipulate 2 PCM connectors to simulate better and worse idle conditions....can even make it die out.....having been an auto mechanic in the 70's, I dealt with the various fuel injection systems by Toyota, Datsun and Volkswagon and the array of issues with computer communication.....I have approached diagnoses systematically....testing voltage and resistance on all input sensors to PCM......none were totally failed, the IDLE AIR Controller was suspect and it's been replaced.....Since I can faithfully replicate the poor idle, hard start and engine dying out by manipulating the PCM connectors, that has to be remedied .....After trying the various clamping techniques without having 100% success....I dismantled the white connector block to access the female pin ends and in the process of pinching each one lightly with fine pair of needle nose pliers.....hoping to have the white block put back together by noon tomorrow...I even have had the PCM bench checked(not just the communication check but it was run with varying input conditions for an hour on the machine) ....it was fine...So i have a few choices, buy a new harness(not), find some connectors with a good lead of wire on it and replace mine or somehow get those female pins in the connector to have a tighter fit on the PCM pins...will keep you posted on how it goes

camoken63

Bad news... laredo is doing the same thing again. Seems to be worse during the time the vehicle is coming up to operating temperature. Will die repeatedly, but re-start. After motor comes up to full temp, problem goes almost away completely. Still thinking iac motor?

camoken63

Sorry this is taking so long guys. Update: Have replaced magnetic pick-up in distributor, cap, wires, plugs, coil, cps, battery. Completely disassembled and thoroughly cleaned (with throttle body cleaner) throttle body, iac motor, map sensor(these were all pretty clean, not much build-up at all). Inspected, cleaned, applied dielectric grease to all visible electrical connectors. Thoroughly inspected wiring harness and grounds. All looks to be in good shape, no chafing or wear spots. Jeep still runs very well until it just suddenly dies. Sometimes will restart immediately and drive as if it never happened, sometimes will take several attempts to re-start. Sometimes it only stumbles and if I can feather the gas in time will avoid stalling. The stalling is NOT always preceeded by stumbling, sometimes it is like flicking a switch. I have read through hundreds of threads concerning this issue trying to figure this out without bugging you guys further but IS THERE SOMETHING I HAVE MISSED? Could the tranny (auto) have anything to do with it? Sometimes the Jeep will just miss a beat but keep on running without stalling, seems there is a hard jerk in the trans when it does this.