I have a 1998 Pontiac Grand Prix GTP (which I ordered/purchased new in 1998) that would die immediately after starting. I found it odd that the "TCS Off" lamp came on and would never go off. I could start and rev the engine to keep it running, and could drive it as long as I kept the RPMs up (one foot on the brake & the other on the gas). 

I was stuck at work when it happened and had a 75-mile trip to make on the interstate and the car ran great at 75 MPH, getting 25-26 MPG so I knew the fuel pump wasn't the problem. There were no "Service Engine" lights but if I cancelled the cruise, the car would die unless I kept the RPMs up. When I got home, I plugged in my Blue Driver and checked for codes and finally found one (P0102) pointing to the MAF sensor.

(By the way, this was the second time within the week this happened. After the first time I used choke cleaner to clean the MAF and the problem was cleared at that time.)

Now the weird part: My MAF sensor is a 3-lead system, the black wire in the middle is assumed as ground (0-5 ohms to batt. neg.), the faded green is assumed to be the sensor lead, and faded red is assumed to be constant 12VDC.

With MAF disconnected, I tested voltage across the red lead at the connector and surprisingly got a 24.5VDC diminishing voltage that slowly dropped to 1VDC. Wow! How can you get 24VDC on a 12VDC system? Then I put the MAF back in the circuit, started the car (yes it idled) and tested the green sensor lead checking for fluctuations when I revved the engine. That voltage stayed at 2.61VDC. I then theorized the MAF sensor was bad because that reading did not change any.

I purchased and installed a new MAF sensor, the car idles, the "TCS Off" light is off, and the green lead voltage now varies when revving between 0.1 - 1VDC (didn't push the testing too much). The red lead voltage was at 12.5VDC.

The question: Is it possible to get 24VDC reading on a 12VDC system? Would that have been a capacitive build-up somehow? Maybe bad circuitry shorting two 12 volt circuits in series? The car runs great and gets fantastic MPG for a 23-year old car, but I worry there may be more underlying issues like old wiring. Any thoughts?

Thanks!