Pontiac Repair: Shifting problems on a 1995 pontiac Trans Port Mini-Van, pontiac trans port, throttle position sensor

Question
QUESTION: Passing gear will not kick in when pushing down on gas pedal. Seems like it wont shift down to lower gear but you can manually pull it down from O/D to Drive and it shifts. Pulling out from a stop shifts good just hasn't got alot of power.Also,when driving along about 55 mph push gas over half way seems like motor shuts off not literally just no power.Hope this is enough info. Any help is greatly appreciated.

ANSWER: Hey Allen:

My expertise is not transmission related I actually try to steer free from anything with red oil in it. But I can answer your question none the less. It sounds to me like more of an engine performance issue and it's affecting the way the transmission is shifting. You said it shift okay but my guess is it's shifting late in the next gear. depending on what engine you have in this van it may or may not have an electronically controlled transmission either way the engine has an effect of the way the transmission shifts. I would try a fuel filter on this first off. If it's lacking power that would be my first guess or and overly plugged air filter. when you change the fuel filter try to blow through it if it's plugged solid chances are that you may have let it go to long and damaged the fuel pump. If the pump is noisy it's on it way out. If this has a lot of miles on it a long shot would be a catalytic converter issue. But I would look at the engine first off and the transmission secondly. Has any service engine light come on? If the engine is running poorly at higher speeds the manifold vacuum is incorrect thus not allowing it to shift properly the non electric transmission uses a vacuum modulator to control the shift feels and if it's an electronic transmission it uses the MAP sensor and TP sensor to shift. If you had a Tp "throttle position" sensor issue it would more than likely trip the light on and set a code. If the map was giving a incorrect reading due to it running poorly it may not trip a code. If this has the 3800 V6 then a MAF could affect the way this is running just like the MAP sensor would. Sorry I'm getting a bit involved her but if you get nothing out of this other than look at the engine first then you learned something... Good luck :)


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

QUESTION:  thanks for the answer. By the way, since i just bought the van today, i'd like to get your input on a few other things. The check engine light did come on after I drove it about 50 miles and it is a 3800 V6. Both power windows in the front do not work. Do you think that both of the motors are bad? I looked at the fuses under the glove box and didnt see any that were blown. Is there something else i can look at before having to buy 2 new motors? Last but not least, any easy ways to change the heater core? By the way, its not really a lemon, lol, it was given to me.

Answer
Okay as for the windows the motors do go bad but My guess is either a bad master switch "left one" or a wiring problem in the pass through between the door and the van on the left front. take out the switch and see if you have 1 constant power and one ground to the switch. You can check the wiring out of the switch to see if that indeed is the problem. The left front window uses a dark blue and a brown wire to run the motor. check it with a volt meter and see if it changes polarity with the switch up and down. I'm not sure what the colors are for the right front on that switch. One of them may be tan and the other yellow? It's been a while since I had one of them apart. as for the heater core that job kind of sucks to do it comes out from the inside of the van and there is a lot of pieces in the way of taking it out. I can't really describe the procedure that well It's been a while since I did one of them as well it's just time consuming.. Good luck on both problems and I think what ever your check engine light was is affecting your trans problem. take it to one of those auto parts stores like auto zone or advanced they will scan for a code for free and at least you know what your looking at/for.