'94 Bonneville runs rough and dies...

[GNRAxlRose88]

Ok, i know this has been discussed alot as i've read the other threads, but i want to explain exactly whats up with mine to makes sure it's the MAF.

The car starts right up with a quick turn of the key. The service engine light will either come on right away, or after about 10 minutes. When it does, the car idles really rough. Sometimes it idles real high and if your not holding the brake down it will literally try to take off. At one time the throttle actually stuck and kept moving the car foreward.

It still does 75 down the highway, and shifts through all the gears fine until the engine light comes on. As soon as the engine light comes on it pops out of overdrive (the shifter itself stays in place but the transmission downshifts) and runs at about 3 grand.

I had a mechanic i know run a scan and he came up with a code for the MAF and a "dead code" for the TPS. I don't want to replace both if i don't have to, and the MAF is fairly expensive.

[HotZ28]

Before you start replacing parts without knowing what the problem is, first let’s try to do some basic troubleshooting.

The TPS is not adjustable per se, however, when you replace the TPS, you do need to check the TPS input & output for proper voltage. The TPS can move slightly on the mounting screws and cause a low or high voltage fault. The TPS is simply a potentiometer used to vary voltage. The best way to check the voltage is with a scanner, but if you do not have access to one, you can use a DVOM. The TPS LIGHT GREY, or (WHITE) wire, is the PCM reference signal and should measure 5.0v with ignition on. (Engine does not need to be running) The BLUE wire will show smooth variable voltage from a closed TB position, (usually .45v), and @ WOT, it should measure between 4.0v to 4.5v max. The BLACK wire is ground.

The harness to your MAF sensor is three wires labeled A, B, and C. (located at the T/B air intake area) It has a pink/black wire (C), a black/white wire (B), and a yellow wire (A). Wire C goes to a fuse in the fuse/relay center under the passenger side dash. Wire B goes to ground. Wire A goes to the PCM.

First thing to check here is the wiring harness & connector for trouble.

Next thing, disconnect the electrical connector, turn key to ON position, engine OFF. Read voltage between wire A and ground. It should be between 4-6 volts. If it is, connect test light between wires B and C. Light should be on. If it is, you have a faulty MAF sensor connection, or sensor. If not, connect test light between C and ground. Test light should be on. If it is on, the ground wire (B) has an open. If not, the pink/black wire (C) has an open.

If the voltage was not between 4-6 volts above:

If it was less than 4 volts, either the yellow wire (A) is open or shorted to ground, or you have a faulty PCM.

If it was more than 6 volts, the yellow wire (A) is either open to voltage or you have a faulty PCM.