I'm wondering if anyone could point me in the right direction here. On My 2002 GT, I do a lot of driving. i currently have 56,000 miles on it. On sunday i drive about 200 miles, after that the car will sit for 3 days before i drive another 200 miles, not starting or moving it ( normally). When i do go to drive it, the car will start fine idle fine and everything. When i begin to drive the car the car drives extremely rough. the car shakes really bad, and you can hear a thumping noise from under the car. The car has new tires, and brakes all the way around. heres the kicker though, after driving on wednesday i will use the car everyday and the car will not do it. I'm wondering if this is the trans giving me an early warning. I will get the trand fluid changed in about 2 weeks... but wondering if anyone else has any ideas.

My 96 Grand AM GT 2.4L was running real rough, but it was constant, I have have this condition several times, the first time it happened it was one of the coil packs the second time it was the other coil pack, the last time it turned out to be either the ignition module of dirty injectors. This last time I had it towed to a Midas shop because the catyletic converter overheated and turned molten red, so I thought I had a clogged converter. I changed the plugs, wires and both coil packs at the midas garage, they wanted $150.00 for just the plugs and wires, so I did it myself. still wasn't the problem. they put it on some diagnostic equipment and fuond the ignition module was bad, I had them put on a used module that one of the mechanics had and they did a fuel injector cleaning and that took care of all of the rough running as well as a hesitation issue I was having when shifting out of 3rd gear and 4th gear. The car runs great and I now wish I would have had the injectors cleaned sooner. This will now become part of my general maintenence from now on. Even if my problem was the ign. module it will not hurt to have the injectors cleaned once in a while.

Since you do a lot of dirving I am going to assume that you sometimes buy fuel ad different places, you may want to change the fuel filter and think about an injector cleaning, you may have gotten a bad load of gas that caused you one time problem(so far one time with any luck that will be it).

Sorry to be so long winded but I wanted you to know most of your possibilities and options.
Good luck,
Dan

Thanks for you thoughts. I've tried the fuel cleaner stuff a few times that doesn't seem to help. I'm 70% sure my cat is shot again, I've been so busy to have someone look at it though, and after i drive it's not glowing so i know it's not that bad yet. I did manage to find some time today to get at least the fluids replaced to see if that's the culprit.