Transmission and Intermittent Check Engine Light

96 Passport w/6cyl automatic.

Driving to work this morning it started to lose power. Stepped on the gas a little and the engine actually slowed down. Took my foot off the accelerator and the engine sped back up a little like it had downshifted momentarily or was about to.

Got on the highway and had no power when stepping on the gas... even worse than the side road... flooring it would bog it down to nothing. Removed my foot from the gas and it would sudenly speed back up again. Couple times stepping on the gas with varying pressure would cause the transmission to shift erradically... first way down, then back up again. Couldn't really get above 70. It's as though the transmission knows you want to giddyup but doesn't downshift till you let off the gas, but then shifts back up again, and when you're on the gas the engine doesn't giddyup, it bogs down.

Right about the same time the check engine light came on. Stayed on till I got to work and was idling through the parking lot, then it went out. The light did this same thing the other night on the highway, came on at speed and whenever accelerating, but went out again when I came to a stop, but the transmission never got freaky on me.

I've searched this forum and there are transmission problems out there, but I haven't found this one. Anyone have any ideas or suggestions so I could maybe point my mechanic in the right direction instead of letting him experiment with sensors/ecm/tcm/error codes?

Which reminds me... is it true that certain error codes are cleared when you shut off the vehicle? Would it be useful for me to drive on the highway, get it to behave badly, and then drive it right to the shop for him to check it?

Thanks!

Which reminds me... is it true that certain error codes are cleared when you shut off the vehicle? Would it be useful for me to drive on the highway, get it to behave badly, and then drive it right to the shop for him to check it?
It woiuldn't make much sense for codes to be cleared when you shut off the vehicle since codes are checked with the engine off.

As for your problem, don't be surprised to find out that your alternator is starting to go bad, especially considering that both your transmission and engine seem to be acting up.
:2cents:

You should have the codes checked. All codes are stored until erased. They don't get erased unless you disconnect the negative terminal on the battery or do it with a scan tool.

As far as your problem goes, Canucklehead could be right, these vechicles act weird when the alternator is failing, but it sounds to me more like a catalytic converter problem. The reason I say this is because the problem happens when you step on the gas. More gas, more air, therefore more exhaust. If cat. is blocked up. Vechicle will run good at idle or low speed and act up when you step on it.

Thanks for the tips so far. Tell me... could it be something even simpler? Could something like a dirty fuel filter or failing fiel pump cause the engine to run fine in nuetral but bog down under load? If the engine was bogging down because of insufficient fuel then the ECU would "check engine" and the TCM wouldn't shift properly, right?

It could be. That's why you really need to get the codes read. Alot of the bigger auto parts store will do it for free, just make sure you write down the codes they give you.
I don't think you'll get a code for insufficient fuel, but you could get codes that are caused by it.

get trouble codes post them and we may be able to help