Hello all,

First time poster here, but trust me when I say I have been scouring the interwebs relentlessly for a couple weeks straight trying to track down this issue.

I bought my 1999 Jeep Grand Cherokee Limited 4.7L Quadra Trac (161xxx miles) about three weeks ago, and of course it ran perfectly the two times I test drove it, but not so much once I took her home!

This is not only my first SUV, this is my first automatic out of 10 cars that I've owned, so I'm definitely stepping into a new world, however I am mechanically inclined.

THE ISSUE:

First off, no codes.
The first sign of any trouble, was on the longest drive I took the car on initially just a couple days after purchase, which was only about 16 miles. Upon exiting the freeway, the car's idle dropped significantly, and nearly died. Once the RPMs bounced back, I essentially had zero power, and it felt like the car didn't want to shift in any particular direction (up or down), almost felt like it was stuck in a low gear and wouldn't downshift. When it would shift it felt like it was hunting, and at times the RPMs would increase without an increase in power.

Upon pulling over and putting the car into park, things seemed to normalize, and I went on my way. The car drove just ok on the way home from this trip, with my idle surging a good bit when coming to stops, and some definite hesitation under load at times.

Against my better judgement, I just took the Jeep camping this past weekend, driving 3 hours each way, during which it performed pretty well, with only a few idle drops and surges along the way.

The Jeep definitely seems to not prefer stop and go traffic, as the issue seems to arise when either coming to stop, or while at a full stop. If it takes off from a dead stop ok, then it seems to proceed through the gears just fine with appropriate power output. But if I feel hesitation off the line, then I know it's not going to accelerate and move through gears properly, and to brace myself to pull over.

It wasn't until today (9/19), where I was ironically coming from an auto parts store, when the car completely died altogether for the first time when at a stop. It died once more about a half mile later while at a stop again (already completely stopped). It starts perfectly fine when I attempt to restart the car, but I'm still thinking it could be either crank/camshaft sensor, or possibly O2 sensors, as my model of Jeep does not have an EGR, and several other items have already been replaced.

Given the previous owner's lack of responding, I went ahead and replaced the TPS and IAC together, while the MAP sensor was replaced by the previous owner, along with spark plugs, coils, air filter, fuel filter, and new 12 hole fuel injectors, along with a throttle body servicing. Now that I know all the things the previous owner replaced, it is likely he too was dealing with an idling issue that he decided not to disclose to me.

Given the fact the idle seems to hunt at times, then randomly drops and surges, and the fact that the car is now dying completely, along with the other symptoms described, I'm thinking (hoping) it must either be a non-obvious vacuum leak, camshaft/crankshaft sensors, or even possibly upstream O2 sensors (hoping it's not torque convertor or transmission related).

I provided my vehicle details in my profile, but I believe I provided all pertinent details around the car above.

Any input around the issue would be greatly appreciated.

 

Bump.

I have since taken the Jeep to a shop, where a smoke test was performed, and several other tests including command of the IAC idle up/down.

What the mechanic noticed was the EVAP purge valve is opening at inappropriate times, while the valve itself seems to be functioning correctly.

After much reading, I was able to determine that the purge valve is controlled by the PCM. Rather than throwing $160 per hour at diagnosing, now that I know which system is malfunctioning, I'd rather throw a few parts at the system in question. I have gone ahead and purchased a flashed PCM, as many indicators point towards the control module.

I will update this thread with any updates once the new PCM arrives. Although I'm being told that all the 'big brand' PCM providers are garbage? Anyone with experience with the likes of Flashmasters, I'd be very interested to hear your insight.

Thanks!

 

Any news?? I was also considering buying a new PCM. Also have idle problems and other weird problems??

 

Obviously I haven't gotten any input via this thread, but on jeepforum.com I have another thread going with many responses.

I'm currently awaiting a 'grade A' PCM that I had to order from a wrecking yard in Iowa (where they test the PCMs for functionality).

I will then need to send the PCM to another individual I have been talking to, who will flash it to my VIN, then send it back to me to install in my car.

Overall the process is a mess, just don't make the same mistake I did and also buy a 'refurbished' PCM, they are all pretty garbage.