Rob116

I'm getting the trouble code for the TPS since I replaced my 305 with a 350. I've checked the voltage and it reads exactly zero, soooo... I figure it must be crapped out. (It also starts to make this fast clicking noise when I hook it up, so I wonder what in the hell is going on) My idle varies by about 100 RPM from 700 - 800. Also, when I really open it up, it starts to "chatter" and stumble. Otherwise it's actually running pretty strong when I lay off a bit. Do you guys think that it's just the TPS or is something else going on? I live in Canada and a new TPS will run me about 60 bucks - cheap, but the money could be better spent considering that I live on a working-student's budget, so I was just hoping that maybe you guys would have some insight into the problem before I fork over the cash. After all, if I spend 60 bucks on the TPS, I won't have the $140 to buy a new set of headers off of my buddy!

Thanks in advance!

99Hawk120

Hey,

Check the voltage on your MAP (or Vacuum) sensor when you have the TPS hooked up. Chances are it's 0V at all three posts when the TPS is hooked up.

The symptoms you describe are EXACTLY what happened to me when the TPS shorted to the body of the carburetor (inside, of course). It turns out that the TPS and MAP/VAC sensor use the same power line coming from the ECM, so when the TPS shorted, it dropped the MAP sensor down to zero volts as well. 0V at the MAP sensor indicates WOT and 0V at the TPS indicates throttle closed, so the poor little ECM's silicon brain couldn't figure out what was wrong.

The chattering is the mixture control solenoid. Ordinarily, the MC solenoid will click for a short period of time on key-on, and constantly while the motor is running. The shorted TPS does something to annoy the computer and basically causes it to go through the key-on steps again (why, I don't know). Normally plugging and unplugging the TPS with the key on and motor off will NOT cause the MC solenoid to start clicking.

Rob116

Thanks for the ideas! I didn't get home from work until late tonight and then it was off to hockey, so I never got a chance to look at it. My dad did look for me though and he says that the vacuum sensor IS registering. However, he has been known to screw up on occasion (read all of the time), so I'll check it for myself tomorrow!

SgtSkip

What are the normal voltages for the MAP sensor? I need to test mine.

99Hawk120

On the Vac/Map Sensor, one will be ~5V, one will be ground, and one will be signal. I mentioned the sensor in the above because ALL THREE will be ~0V if the TPS is shorted.

As far as the signal itself, measure all three lines with the car off and the car at idle.

In one condition the signal will be high (~4.5V) and in the other it will be low (less than 1V).

IIRC, which condition registers the high signal is what determines whether it's a MAP sensor or a vacuum sensor. FWIW, mine measures high at idle with vacuum present.