cant get TPS to reset to 0

[bigfatls6]

Im trying to tune a 99 fbody and cant get the tps to reset to 0%. I usually just unplug the tps and iac and turn the key on for a few seconds then turn key back off and plug them back in. Then turn the key back on clear the codes and the tps is reset to 0. this car has a previous history with the same issue. The old tps sensor that was on it was drilled a little to where you could manually adjust the sensor a little. Has any one else ran into this issue with a car? if so what did you have to do to fix it? Im trying to tune the idle on the car but I need to open the throttle cracker to get more air in. I don't want to have to drill a hole in the blade. already installed another Known good TPS sensor. For some reason I just cant get the tps to reset like normal.

[bigfatls6]

The car had a stock ls1 with a mid range cam before so they only cracked the throttle body open a little and then drillled a huge hole in it. The car now has a 408 with a healthy cam and a fast 102/102 set up.

[Montecarlodrag]

Open the scanner and log TPS volts with closed throttle

If TPS volts are above certain value the TPS will not reset to zero no matter what you try.

[bigfatls6]

Open the scanner and log TPS volts with closed throttle

If TPS volts are above certain value the TPS will not reset to zero no matter what you try.

thanks Ill try that.

[bigfatls6]

Ok with the throttlebody all the way closed it is still at .69 volts. What value would be too high to reset? If I remember the volts should be around .64 with the throttle body closed. Would I need to adda resistor to the circuit or something? this is wierd. am I missing some thing here. I turned the throttle body all the way closed to where it starts to stick a little and its still at .69. do I need to change a setting for the 102 throttle body? Its a drive by cable.

[Montecarlodrag]

0.69 is not that high.
Unscrew the TPS and slot the holes so you can turn it in the same direction the TB opens (to make it read lower).
Go little by little until you see 0.59V or something close

[bigfatls6]

well I notched the holes and adjusted the tps and got the voltage down on it. I can reset the tps now but it keeps going back to 1-2% tps at idle. Why the hell does it do that? Its a cable drive tb in an fbody.

[planethax]

reflash vehicle

[LSxpwrdZ]

Verify the shaft doesn't have play in it and make sure the bump stop is the same everytime. Sometimes the cam the cable rides in will get loose and allow the blade/shaft to rotate freely even though the cam is on the bump stop. I had alot of trouble out of older FAST throttle bodies doing this. If all that is fine try replacing the TPS sensor. I had a 98 TA once that would jump around all over the place and swapped the TPS sensor and never had another issue out of it.

[262]

Bad TPS sensor. Have seen many of them do this now. If your TPS voltage is good yet it will still read a % value toss that sensor away and start with a new one.

[planethax]

Just had one in having this exact issue.
Tps read .65V (which is valid) but no matter what I did the Pcm was reading + 1-2%
Even disconnecting the battery would not reset the PCM

I reflashed the Vehicle and then the PCM read Tps at 0%

[bigfatls6]

Just had one in having this exact issue.
Tps read .65V (which is valid) but no matter what I did the Pcm was reading + 1-2%
Even disconnecting the battery would not reset the PCM

I reflashed the Vehicle and then the PCM read Tps at 0%

I have reflashed it a few times already had 3 different tps sensor on it also. Im about ready to throw my hands up on it. Ive never seen this issue before. I can unplug the iac and tps and reset it to 0 and the car will idle fine. As soon as you fire it up and let it run the tps % will jump up. It was already screwy that I had to notch the mounting holes on the tps to get the voltage low enough to reset it. If I bolt a tps sensor on where it is supposed to go the voltage is in the .80 range. The throttle body is a NW 102. BUt this same car with a stock tb when it had a heads and cam ls1 in it had to have the tps sensor mounting holes notched also so IM not sure if its an issue with the tb.

[planethax]

Strange.
I will say that when I reflashed the vehicle I did not use HPT but a Tech2 with the latest software.

I do not believe it is the TPS or TB because the voltage 0.69 should be with in range.

Do you have a stock tune to try?
Wondering if either your tune is corrupt or just a Malfunctioning Pcm.

[LSxpwrdZ]

Check and make sure all your grounds are good. Any kind of small voltage fluctuation can and will cause issues for sensors. If you have another PCM to try stick it in there and see what it does.

[mecanicman]

With key off unplug the iac and tps. Turn the key on for 10 seconds. Turn key off and plug back in. Read it out of the gm manual some time back.

[planethax]

With key off unplug the iac and tps. Turn the key on for 10 seconds. Turn key off and plug back in. Read it out of the gm manual some time back.

I think he has done this, however, once running the % rises.

This is why I think it may be a faulty PCM unless Voltage fluctuating faster than scanner can see?

[LSxpwrdZ]

Put a multimeter on the 5v reference of the TPS and monitor it while this issue occurs. On a healthy PCM the voltage should stay regulated to a very precise tolerance. If the TPS has been changed multiple times and is known to be good then the reference voltage or ground has to be causing issues and should show it's face with this reading if it's the "+" side.

[68Camaro]

check bearing on opposite side of throttle body blade shaft. I had one go bad once letting the shaft wink just enough when engine was running to cause this - engine off no problems only when vacuum present back side of blade.

[79 z28]

Revising this thread, I have the same issue....
Nothing wrong with the sensors or the TB ..... Its a big cam and needs air in order to idle. There is NO hole drilled in the TB blade so the adjust screw on the TB is used and the TB blade is open slightly and reads accurately at 1%. Does this effect the throttle cracker or follower in any way? The TPS step size is 1%..... what is effected ? I cant get my car to idle if I come to a quick stop. It will drop down to far and not recover.

[DSteck]

I'm actually going through this same thing on a 99 big single turbo Camaro with a TH-350. It's annoying as hell. If I figure it out, I'll post up what I did.