So short version, all of a sudden my car will not start. Diagnostic shows TPS reads 98% at idle. 4.84V to the TPS key on. TPS resistance sweeps from .9kohm to about 6.4kohm smoothly all the way. Car starts fine with TPS unplugged.

What resistance values should the TPS have?

Long version. After a recent car show I was running a bit hot 205F at idle and climbing (over 200F is hot for my car). I noticed my cooling fan was not functioning and I traced the problem to a melted relay connector. The car sat for a week or so waiting for parts. I soldered in a new relay connector and set my ECU (stand alone FAST ECU) to turn the fan on at 50F to see if it would function. The fan would not turn on with just key on, so I figured I needed to start it. Well, no start. Have good fuel pressure on the rail and can't diagnose any issues with the MSD ignition box. I plugged my laptop in and noticed that my TPS was reading 98% at idle position. Usually it reads 12%. With this ECU high throttle on cranking shuts off the injectors to clear floods. So I unplugged the TPS sensor and showed 0% throttle as expected. Car then starts right up and idles. Oh and the fan works lol.

Do TPS sensors fail in this manner? I will put a new one on tomorrow just to check, but I was curious about others experiences and input. I appreciate it.

 

I’ve gone through a few to the point I always have one on the shelf. I’ve also had to replace the 3 pin connector on the cars harness side.

they get dead spots sometimes and you’ll feel a hesitation off idle. I’ve never had one fail to full open though.

You can remove them and test with a multimeter (like you did) but it’s very hard to see any dead spots and still leaves the issue of a bad connection internally or on the harness side.

i only buy the ac delco ones.

 

I appreciate all the tips.

So I tried cleaning and slightly tightening the connections on the TPS and there was no change.

I also looked carefully at my resistance measurements and they dont make sense. Almost as if the sensor is backwards. Resistance is lowest on the idle stop and highest at WOT.

I picked up a new sensor and checked it's resistance values. They make sense and are opposite from my old TPS. I plugged it in and it works perfect. Clean smooth sweep from 0% to 100% as displayed on my laptop via the ECU. This is certainly a very strange failure mode for this type of sensor.

I am guessing I have a bit of retuning to do now. Old idle was at 12% (non slotted TPS). New idle position is set at 2%. I am hoping since I am running speed density it will be minor. To my knowledge TPS input is not a major player on those tunes.