I have a 2000 z28 and sometimes when I start the engine the SES light comes on, sometimes it doesn't. When it does come on, it usually stays on for about 30-45 minutes of driving then it goes out. Sometimes it doesn't come on at all. I went to Auto Zone and had it scanned, its showing three codes. po122 (TPS/Pedal pos sensor), PO172 (too rich, bank 1) and PO175 (too rich, bank 2). Is there a way to test the TPS or should I just replace it? Or is the problem somewhere else?

 

You can test the voltage coming out of the sensor. Look up the throttle bump stop mod on the boards and it will tell you more. basically, at full open throttle it should tell the computer 1.00 volts, but sometimes the castings of the TB's only allow the throttle plate to move far enough for say .98v. so you grind off some material till pedal to the metal reads 1.00 v. hope that one makes sense. this is one of the free mods you can do, so try lookin up that as well.

 

not real sure what it is but a place to start...If you can find somebody near you that has auto tap, get the TPS reading and see if its reading correctly. I'm not sure about the correct voltages for WOT and closed (or idle throttle) but the install university web page has them i think. just a guess but maybe the TPS reading being off could throw codes in the os sensors as well. For example the TPS says the throttle is closed but you are actually driving down the road at like 300 RPMs with part throttle (or WOT if youre flooring it) so the O2s see readings for what is actually comming out in exhaust gas. The two don't match up. The Computer says that ain't right and throws the codes. Just a guess. Good Luck

 

WOT TPS voltage should be no more than 4.70. Closed throttle is around .6 I think. Check the light blue/white stripe wire.
It sounds like this is an intermitant problem. Maybe the TPS connector is loose or dirty.