88 5.7 TPI IROC

For a while, I was throwing a code 23 (23. Low temperature at manifold air temperature sensor OR Throttle position sensor error). The code only came on if I let it sit there and idle for a while (10 minutes ish), or if I stopped at a light for about 30 seconds after driving normally. It was pretty consistant. Considering the car is usually kept in the garage as it's not my daily driver, I didn't get around to changing that for a while.

Went to take it out a week back or so and it seemed like it was flooding. I'd step on the gas at idle and it'd bog and you could smell the gas. After I got it to idle on it's own, I let it run for a good 10 plus minutes and then drove it around and all seemed fine. Drove like a champ.

The next day I started it again with the same problems and just didn't have the time to deal with it. Now it seems it's not getting much fuel or fuel pressure (best guess, as I'm not a mechanic). It will kick over once or so, but that's it. Also threw some gas in the tank just to make sure it wasn't just a broken fuel gage. No luck. Just kicks over once (usually) and turns off. Sometimes it just doesn't catch at all and will just crank away with no results.

I can't be sure, but I don't hear the fuel pump turn on with the ignition. I've checked all the fuses under the driver side dash and they're all good. As a prayer, I picked up a new TPS sensor and put that in. I didn't calibrate the TPS sensor yet, but I'd assume it's not far off, at least not enough to make these results.

So any ideas on how to make sure what this is? If I remember right, a fuel pump job costs bout $400+. Or it would involve me dropping the empty tank, the exhaust, and part of the suspension. I'd just like to take the right steps to at least pin point the problem before I get this project on. Not sure exactley on how to test the fuel pressure going to the engine, or where any relay's and wires are and what voltages they should have.

Any help would be appreciated.

 

DTC 23 is a low temperature error for the MAT sensor. Usually, that neams an open circuit from a failed or disconnected sensor, or cut wire. You can remove the plenum and replace the MAT sensor, or install a second MAT sensor in a different location. Before getting that far, however, diagnose the problem and find the real cause. There are a couple of places that the sensor could be disconnected.

If the problem is a failed sensor, this might give you some ideas:

MAT Sensor.pdf

 

IIRC, the MAT makes little difference in fuel mixture on most MAF cars, but since your's should be one with no cold start injector, the ECM relies more on the MAT input for added starting fuel calculations, and could contribute to your hard starting problem.