Throttle Body has no Power
 

Hello!
My 95 S320 (made in late 94) is currently sitting in my auto shop because myself and my mechanic are befuddled with this and here is why:

The car started moving with a stop-and-go motion just jerking suddenly, not moving out of 2nd gear.
The car has never done this before, no transmission issues either.
My mechanic determined that the fuel rails we not holding fuel pressure. the fuel pressure regulator has been changed and works fine.
At first, we though maybe it was a fuel pump so the car was basically choking like a fish with little to no water and then we figured out that the throttle body was also acting up.
The throttle body has no electrical input from its plug. We checked to see if the throttle body still worked by applying power to it and it works as it should aside from not having power when it is plugged it.
The relay for the throttle body also works and has power. The wiring harness going between the two is one that typically does not go bad.
After checking these things, we found that the over-voltage protection unit in this model is part of a computer which was not working. It was not letting the throttle body and fuel pump work. We replaced that unit and it worked for a couple minutes before the car started jerking through the parking lot.

So now, my question is, why has this part gone bad a second time?
My theory lies in something to do with electrical connections that are sending the improper voltage. Low or high? I don't know. I don't completely understand what Diodes are, and same with resistors or what they look like. I don't even know if I'm looking in the right place but I'd like some feedback to let me know if I might be on the right track.
Also, could anyone tell me what direction these electrical connections come from? Where does my over-voltage protection unit that controls the fuel get its power? Is the power directly from the alternator and if I need to look at a resistor? Where would I find it and what does it look like?

The throttle body is driven directly form engine computer. I want to say it is the first one from the front of the car, and it is a fat-one. It will have a label 6cyl or 6z... on it...

In your case, I would see if you have a updated engine wiring harness as all bets are off if have a old harness. The revised engine harnesses have a DELPHI white tag on them...

The other quickly cheap test is to go to the Pick N Pulls of Sacramento Area, and pull a computer from a S320 around the same year, but not a 97 and above, or a C280 of around the same year even a E-class W124(six inline engine) of the same years as the engine software is the same.

Martin

Thanks! I do not have a way to currently drive to my car right now to check the computer. Are you saying that it is the computer in front of my engine or the first computer in the box in front of the passenger side firewall? I will try to test that connection to make sure it is there and working or not working. So is that computer protected from any voltage issues like a short? If that computer is bad, another concern I would have is, what made it go bad and if there is anything I could change out to fix the problem?

I would suspect a wiring harness issue if it is original.

does it have a pedal posistion switch? Mine does it works the throttle.

It does not have ASR so the pedal position switch does not effect it because it is mechanical. I did just find out that the throttle wiring does not run volts, it runs ohms so we could not read it with a voltage meter. The reason why the throttle is choking my car of fuel is because it has a fuel safety shut off switch. The switch is being shut off once I try to put a little more rpm or gas in the car because the wiring is bad and will cause the switch to shut off fuel. The mechanical portion of the throttle body unit however does work.
Because of this, I would like to rebuild my throttle body by changing out the wires in it. The wires are badly rotted by I'm not sure what materials I need to buy. Would anyone know?

Replace engine wiring harness.