8587ta

I have an '85 Trans Am with a TPI 305, I bought it about 2 years ago and haven't got to drive it yet. It ran when I bought it, but not very well. I rebuild the distributor with a new pick up coil, cap, rotor, coil, and then put on brand new 8mm wires and new plugs, new fuel pump, new fuel line, new fuel filter, adjustable fuel pressure regulator, cleaned the K&N air filter, Heat/AC box delete, the smog and emissions were gone when I bought it, new battery, anyways you get the point, I replaced a lot of stuff, it will start, it will idle at different speeds everytime I start it, sometimes I can got to WOT, other times it quits if I touch the throttle, or sometimes it bogs down and backfires a few times. I checked for codes and only got code 12. I tryed to set the IAC and the TPS and I got it to idle around 450 to 500 beautifully, but if I touched the throttle it died, so I unhooked the battery for the night and tryed again the next day and it was right back to 1100 rpm to 1500 rpm idle and would go all the way WOT. So I have NO idea what's going on with it, the timing is set and seems to be fine. Everyday it does something different. Please let me know if you can think of somethings I can try. Thanks!

Eagle223usa

Are you throwing any codes?

ASE doc

It should be setting some code. However, sometimes we get what's called an "in range" failure where a sensor fails to read correctly but doesnt go high or low enough to set a code. This was a big issue with older systems where the only codes for any part failure were "voltage high" or "voltage low". In cases like these we just have to choose a like suspect and start testing. In your case, I would look for an issue with the TPS or the IAC.

The TPS is the most likely suspect since it affects the throttle tip in fuel enrichment. It should of course read .45-.55 at idle and smoothly ramp up to 4.5 volts at WOT. Look for any glitches or drop outs, especially just off idle since thats where your problem seems to be. You really want a lab scope for this test but an analog volt meter will work.

8587ta

Ok I re-pulled the codes last night (I forgot to wait for code 12 to flash 3 times) and they were 22 and 54, I can understand the 22 when I pulled the codes because I have the TPS currently unplugged so I could remove the throttle body and clean the IAC and it's airway...which had a ton of carbon build up on it. But the 54 is where I am looking next. I know the PO put in a new fuel pump to get it running before he sold it, and he told me it wasnt the correct fuel pump for that car but the parts store said it would work temporarily. But it primes when I turn the key and it puts plenty of pressure to the fuel rails, so I am wondering if either the fuel pump relay or the oil pressure switch is defective. I also noticed my fuel gauge always says full...so maybe even a bad connection somewhere? But I plan on putting my throttle body back on today and adjusting the TPS and IAC (now that it's clean) and then recheck for codes. But I have a feeling that the TPS is faulty (and expensive). I will keep you updated on it, and Thank you very much for the help so far! Oh and one more thing, the spring in my IAC looks like its compressed in the middle and not on the ends...I will try to show you with some slashes and L's... l//lllll//l something like that. Any thoughts or is that how its supposed to be?

ASE doc

Test voltage from the oil pressue switch, tan/wht wire while engine is running. It should be at least 12v. Any high resistance(poor connection, partially broken wire) in the fuel pump circuit between the battery and the oil pressure sw can cause this code. A high draw on the circuit, such as low pump impedance can casue the code as well. Checking voltage at the oil pressure switch will point out the low voltage. You will have to perform further testing to determine the cause.

Check all wiring to the fuel pump relay, check the fuse next to the battery on the inner fender well. Check the wiring fromt he relay and from the oil pressure sw to the fuel pump. I believe the fuel gauge sender ground is seperate from the fuel pump ground but you should take a close look for any problem around the tank. The steady high fuel gauge reading is either an open sending unit or sending unit ground.

Also be sure to test the TPS as I explained earlier.

ASE doc

To properly diagnose this vehicle you need a correct wiring diagram.