TPS Sensor/Driveability problem

jdillen · 09-02-2008, 10:26 AM

Alright so I have a 91 TSI AWD I picked up a few months ago. It's undergoing a slow diagnosis/updating. I have done some searching just to get that out there. When I got the car it had the infamous idle surge, but upon doing some things that has gone away. I now have a high idle at startup (like 1800-2k) that will come down to the 800rpm mark as its warming up. The main issue I've been struggling with is when I take the car out for a diagnosis lap around the block and it finally hits peak operating tempertaure the car will idle really bad then fall on its face and the car will die. Or while driving if I let off the throttle (throttle plate goes shut) the car will rapidly drop in RPM and die (basically no idling in neutral).

When I start the vehicle up initially I'll generally get a CEL to flash on but as soon as I touch the gas pedal (just a touch of the pedal) the CEL goes away. Only to come back again when idling (and will go away as soon as the gas is touched and will not come on while driving the car). I'm confused as to why the CEL goes away when I touch the gas pedal and wondered if maybe something is amiss with my TPS sensor. The car doesnt appear to be acting weird when idling before its fully warmed and the CEL is on. So I figured I'd test my ISC and TPS sensor and clean my throttle body. I did this yesterday. The ISC tested fine with all pins reading within spec. The TPS sensor though, I'm confused about its readings. I tested in accordance with the tech/vfaq info. Testing initial resistance (pins 1& 4) it reads right at around 5k ohms which is in spec. Testing pins 2 & 4 with the throttle completely closed it read 216. The spec says it should read .9k-1.1k ohms. This has me stumped. With the throttle fully open, it reads right around 5k ohms which is in spec again.

So does the fact that the sensor is reading very odd at closed throttle position at pins 2 & 4 possibly relate to the issues I'm having in terms of driveability? Possibly unrelated but my sensor is still bad? Any advice/diagnosis help would be appreciated. Thanks.

bobster22388 · 09-03-2008, 04:18 PM

Im having this same exact problem right now on my 92 gsx, i came to the conclusion that it might be the tps also so i bought a new one today and im going to give that a try. ill let you know if i found out anything else. glad im not the only one...

jenglish1984 · 09-03-2008, 04:35 PM

sounds like your TPS is out of adjustment mate. grab a logger and set the TPS at 10% and see if your CEL goes away.

need2boostpsi · 09-03-2008, 04:36 PM

Quote:

Originally Posted by jenglish1984

sounds like your TPS is out of adjustment mate. grab a logger and set the TPS at 10% and see if your CEL goes away.

well said

jdillen · 09-05-2008, 11:46 AM

Well, I hadnt checked back to this thread before working on my car Wednesday but I did get some progress. I cleaned the throttle body and biss screw/oring and put the sensors back on and just retested them again. ISC good to go. For whatever reason I was getting totally different readings from the TPS sensor (in a good way!). I adjusted the TPS manually as stated in the vfaq so that the resistance between 2 and 4 was .9kohms at closed throttle. All looked good so I reinstalled everything.

Started the car up and after a few seconds the cel still came on and when i touched the throttle it went away. Upon warming up, the car started to begin to lose its idle as noted before so i thought i should readjust the biss since i had taken it out. I reset the BISS and the car now idles right around 850-1k rpm pretty regularly. I took the car on a longer drive than normal and feels good. I still would like to figure out the cel issue. I'm replacing my o2 sensor and spark plug wires as regular maintenance and so after that I'll go to working on getting the code figured out. Thanks for your help and feel free to chime in with other suggestions.

RSTurboFWD90 · 09-05-2008, 06:05 PM

Any codes stored?

jdillen · 09-07-2008, 03:03 PM

I dont have DSM Link or a logger at this time to see what the code is. I'm eventually going to be getting one of the two in the coming months so that'll help out I'm sure.

RSTurboFWD90 · 09-09-2008, 11:30 AM

Yes. Knowing the code(s) will be a big help. I was initially interested in your problem because a few months back I had similar CEL behavior. Code said knock sensor; replaced it and no more CEL. It also seems to drive a bit smoother now.

steve · 09-09-2008, 03:23 PM

Quote:

Originally Posted by jdillen

For whatever reason I was getting totally different readings from the TPS sensor (in a good way!). I adjusted the TPS manually as stated in the vfaq so that the resistance between 2 and 4 was .9kohms at closed throttle. All looked good so I reinstalled everything.

It's too bad that the VFAQ is wrong.
It's only by dumb luck if you wind up with the correct adjustment.

On a 1G you need to set the TPS to output about 0.5v at idle. You can do that with a SAFC, Datalogger, or voltmeter. The SAFC will show you the measured TPS voltage on the Sensor Test screen. The datalogger will report what the ECU measures either as a voltage or a percentage (0.5v out of a possible 5.0v is 10%). It's hard connecting the voltmeter probes but you can do so at the ECU connector between pins 19 and 24.

jdillen · 09-10-2008, 09:59 AM

Quote:

Originally Posted by steve

It's too bad that the VFAQ is wrong.
It's only by dumb luck if you wind up with the correct adjustment.

On a 1G you need to set the TPS to output about 0.5v at idle. You can do that with a SAFC, Datalogger, or voltmeter. The SAFC will show you the measured TPS voltage on the Sensor Test screen. The datalogger will report what the ECU measures either as a voltage or a percentage (0.5v out of a possible 5.0v is 10%). It's hard connecting the voltmeter probes but you can do so at the ECU connector between pins 19 and 24.

Wonderful....thanks for the response. Well time to make a logging cable and get at it. When I get it all setup I'll report back to update this.