P0108 and P0121

[Bob Keyes]

Hi All, My 97 SSE is throwing out these 2 codes. P0121 TPS and P0108 MAP. On one occasion the idle went high by itself and would not return to normal until I shut the engine down. Started back up and it was fine. There does seem to be some intermittant hesitation from idle too. Other than that my fuel mileage seems a bit less than normal. Is there an easy test for these sensors? Which one should I look at/replace first? She is pushing 150k.
Thanks!

[myfirstbonnie]

The TPS is fairly easy to check. You just need a multimeter and check the resistance and it should increase without any large jumps or stutters. With it on the car you want to adjust it to around .4 volts when the TB is closed and the key is in the run position. Then cycle the TB fully open and you should have almost 5 volts.

[Bob Keyes]

Over the weekend I had some time to mess with this thing. First, I found a vacuum tee with a big split in it. I replaced it hoping my problem would be gone. About 40 miles later there is the mil again. Same 2 codes 0122 and 0108. So I pulled the TPS took it to the bench, applied 5 volts to it and measured output voltage as I rotated the internal mech. The voltage steadily increased with no hicups etc. Is there a way to check the map with out a vac gage? Or any other ideas???

[Bob Keyes]

Yesterday I had cleared the codes out before I left work. I drove about 40 or so miles home with no mil. This morning about a mile down the road it came on. I drove about 1 mile or so to the school to drop off my kids, turned it off and checked codes. PO108. So, is it reasonable to assume that the MAP is bad and thus sets the PO1O8 then the TPS code gets set after it tries to compensate for the bad MAP?? I don't know if this makes any sense!!

[Mechanical Mike]

The MAP sensor also gets 5 volts. The voltage should vary between 2 volts at idle & 4 volts with key on engine off. Carefully check the vacuum line going to the sensor. If the NA & supercharged engines use the same sensor then there's a T built into the bottom of the sensor & a cap covers one side of the T. Make sure that cap isn't missing or split open.