OK, new to the forum, so I hope you can help. I have an '01 Grand Cherokee Laredo with the I-6, & 4WD. Absolutely wonderful vehicle, as she has 218,000 on it and still running good.

Anyway, there are two things are going on right now that concern me. First, at highway speeds I can accelerate and the tranny drops down and immediately back up, almost like the old 4 barrel carbs used to do when you floored them. I also have the problem happen when I am cruising down the highway with the cruise control on. I basically constantly drops back to 3rd and immediately goes back to 4th/OD. To the point that cruise control is useless. This happened a long time ago and the dealership installed some kind of new module that ended up costing me about $250 with parts & labor. Obviously I need to do this myself if at all possible.

Second issue happened last night while in a drive through line. As we crept along, it really started vibrating, almost like it was something in the fuel line. But, when I put it in neutral, it stopped. Put in drive, it vibrates and hesitates like crazy. With cars in front of me and cars behind me, I had to do this the whole time for fear of it shutting off. About 5 minutes after it started, it was gone and she purred like a kitten again. So far I haven't been able to get it to do it again, but with Christmas shopping and this being the wife's DD, I want to find a fix ASAP.

Could these both be the result of a bad module or sensor somewhere or am I looking at two separate issues that someone beyond a shadetree mechanic (me) needs to look at?

Thanks in advance!

 

You might check all your vacuum lines are connected, tight and no leaks.

 

I'll check them today. I appreciate the quick response!

 

What ever your problem is, it's temperature related. Idling in line will cause the electric fan to engage to limit the engine temp. Check your IAT (intake air temperature) sensor. It may have something to do with your poor idling response.

My WJ's electric fan is slightly out of balance so when it engages, it shakes the steering wheel and pedals a little. It feels like a cat purring when you put your hand on it. I did notice there is a little balance weight clipped to one of the blades of the fan, so it probably was out of balance when it was made.

As far as the cruise control is concerned, mine will occasionally shift out of O/D on hills at around 65 mph, but not often. I think that is caused by the TCM (part of the PCM on ours) detecting vehicle speed as compared to engine vacuum draw. If vehicle speed drops and the throttle is open too much, the trans will downshift. This happens quite often if I'm heavily loaded. This info is just to give you a starting point to diagnose the problem. I hope it helps. With the mileage you have on yours, you might be a little down on power. I only have 145K on mine.