I hope there's an easy answer and this isn't as much of a puzzle as I think, but I'm sure stumped.

Hope I can explain this adequately:

Though my '89 GXL was running fine, the check engine light was on (throwing both "bad TPS" error codes, btw). As check engine light=won't pass emissions, I had to replace the TPS.

I bought a used TPS on eBay, and then, while the car was running, plugged it in in place of mine. Check engine light went off, car continued to run fine, and I drove around the block to make sure. No problems. New TPS worked and threw no error codes.

BUT - it turns out the car will NOT start with the "new" TPS plugged in. If I plug the old throwing-an-error-code one back in, car starts rights up, but the light is back on. If I plug in the new TPS while the car is off (or turn off and try to restart once the new one's in), the car won't start (so I'm not sure if the check engine light problem is fixed in that case). It tries and tries and tries but will not fire up. Really seems like a CPU/electrical thing.

So, any idea what's going on here? Why would the new TPS solve my problem, apparently work fine if the car's already running, but then prevent the car from starting?

It's just not realistic for me to every morning start the car with the old TPS then plug the new one in to drive.

Thanks in advance.

 

Remove the negative battery terminal, hit brake pedal a few times, hook it back up and try again. S5's tend to store them and don't like removing the code unless the ECU is reset (basically it runs out of power)

 

Do you mean the error code that my original TPS is throwing? Cause it's not there anyway with the new TPS. Car just won't start, but it runs once started with that TPS.

Sorry if I misunderstood.

Thanks for the help.

 

Do it anyway, the s5 ECU can be a pain sometimes, then I'd suggest whipping out an ohm/volt meter and see how the new TPS reads at 'closed' throttle

 

Hows the idle? Silky smooth or kinda up down?

 

It's up and down w/ the original, bad TPS. Was nice and smooth with the new one, at least for the 10 minutes I had it in, but in all fairness I did occasionally have periods of smooth with the old one, too.

 

Your TPS just needs to be adjusted. The easyiest way is going to be.

1. Plug in your old TPS and warm up the car.
2. Plug in the new one loosen the nut on the adjuster adjust the screw out till its near the end of the treads.
3. Start the car the idle will go nuts probably bounce 500 +/-. with the car running squish the two brakets together until you get a descent idle. Adjust the screw to that position.
4. Find the line between good and bad idle. Adjust 2 full turns in from there.

You should be damn close to money from there. After you can get out a meter do some fine adjustment via the how-to's on the site. But I was dead nuts with the light test on the method I just told you.

 

You guys were right - the ECU just needed to be reset. All good now . . .

Thanks, both of you.