Chrysler Repair: bucking when accelerating: 07 Pacifica, rear brakes, auto parts store

Question
QUESTION: 2007 pacifica, when accelerating hear a thump, like someone hit the back, goes away after one thump, kind of like a buck. check engine light came on, repair shop reset, checked trani fluid, said ok, but still bucks. when it first started to happen, it felt like my rear brakes where hanging the back end up from going. transmission slipping? seemed like once or twice around the thumping time, the engine reved, like out of gear. automatic trani by the way. transmission issue?

thanks

ANSWER: Hi I,
If check engine light comes on again don't reset it rather find out the fault code by turning the ignition switch:"on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then see if the mileage in the odometer window changes to show a 4-digit number preceded by a P. That would tell us what the on-board diagnostics think is going on. You could try it now just in case the code has been stored again. That is the best way to get a handle on such a noise. One possibility is that the torque converter lockup clutch is sticking in closed position and then releasing, but there will be a code for that. So let us see.
Roland

---------- FOLLOW-UP ----------

QUESTION: well thank you for your super fast reply.  The code apparently is not stored.  Can I just continue to drive the car with the buck, and see what happens down the road?  I hate to have to take it in somewhere and be at the mercy of a shop with a possible complex diagnosis or repair.

Answer
Hi I,
If you can predict when it happens, or do something that causes it to happen, that is when to take it to a shop for their diagnosis. I doubt you will get much help until a mechanic can experience the problem.
Did the odometer show the words "done" or something that indicated there were no codes and that the readout try worked? If not then try a free code readout by a plug-in reader at an Autozone or similar nationwide auto parts store.
Roland