IAC / TPS Problem?

Synned · Aug 30, 2008

Hey guys

My car is acting pretty weirdly. When I'm driving, the car will start to shift later and later, and the idle will get higher. If I'm at a light, and I put it in neutral, the rpm's will raise a few hundred. The weird part is, if I shut off the motor and restart it, the problem will be temporarily fixed. The shift points are later and the idle is higher. TPS?

HISSIN50 · Aug 30, 2008

If the TPS read artificially high, it should shift earlier shouldn't it (because the EEC thinks you've revved higher than you are)? That's a cool question for Wes, Grady, et al. Does the trans act normally otherwise?

That aside, what you've described can be a sign of a bad TPS. The wiper degrades and the idle creeps up as you drive. Shutting the car off and turning it back on (to have it act normal again for a little bit) is a tell of the TPS being at fault. I'm not sure that's your issue here Joe however (if you have a free/spare TPS, toss it on. Otherwise, I don't want ya to waste money on an educated guess on my behalf).

toyman · Aug 30, 2008

HISSIN50 said:
If the TPS read artificially high, it should shift earlier shouldn't it (because the EEC thinks you've revved higher than you are)? That's a cool question for Wes, Grady, et al. Does the trans act normally otherwise?

As I'm still trying to get a handle on this stuff I could be wrong. I believe the shift is related to the throttle % which is determined by the throttle volt range and vehicle speed not engine speed (rpm). For example if1v is closed and 4.6v is fully open and the TPS sensor is on its way out such that as it opens the volts do not increase the ECU would read that lower voltage as a lower % open and not command a shift resulting in a delayed shift.

That aside, what you've described can be a sign of a bad TPS. The wiper degrades and the idle creeps up as you drive. Shutting the car off and turning it back on (to have it act normal again for a little bit) is a tell of the TPS being at fault. I'm not sure that's your issue here Joe however (if you have a free/spare TPS, toss it on. Otherwise, I don't want ya to waste money on an educated guess on my behalf).

If you have a DMM you can test the TBS for its voltage range. Closed should be about 1v and the voltage should increase smoothly as the throttle is opened to about 4.6v.

HISSIN50 · Aug 30, 2008

I see your point. The higher TPS reading could correlate to a higher load calc, and it would hold the gear longer.

The bottom line is that if the TPS doesnt generate a code, it should be ok (the RATCHET function occurs at all times while driving AFAIK).

Note that this is me postulating - the tuning guys know for sure.

Synned · Aug 31, 2008

Aight guys, Im gonna pull the codes today and see what I get.

inphiniti · Aug 31, 2008

the TPS should be reading around .996-.998 correct? and if im not mistaken, if its off just a .1 of what it should be, it could set off the car... i think my cars running @ 1.0, car runs like ****...

i could be wrong, its only what i was taught... school me if im wrong

toyman · Aug 31, 2008

inphiniti said:
the TPS should be reading around .996-.998 correct? and if im not mistaken, if its off just a .1 of what it should be, it could set off the car... i think my cars running @ 1.0, car runs like ****...

i could be wrong, its only what i was taught... school me if im wrong

There is quite a large range that the PCM can adjust to. Off the top of my head it's about .6v to 1.25v in the closed position with .98 being in the middle of the range.

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