E300 won't downshift, low power, p0120

[benpender]

Hi,

I have a 96 Ew300 with 169k miles. It has run very nicely, but I have noticed recently that its low on power. It also shifts up smoothly and doesn't slip, but it refuses to downshift, for instance, if I'm cruising along at 40mph and decide to accelerate, I can floor the accelerator and even that won't make it downshift from 4th to 3rd.

I pulled the trouble codes and got one for the glow plugs, P0380, I think, and a P0120 which indicates a problem with the throttle position sensor. I cleaned the connections at the TPS near the brake master cylinder without improvement. The vacuum lines appear to be in good shape in that area, too.

I had read somewhere that the TPS might be related to the EGR, so I removed that and cleaned the vacuum operated throttle there, made sure all the vacuum connections and electrical connections there were in good shape, again without improvement.

I also have issues with air bubbles in the fuel system. There were lots of bubbles and I replaced the strainer/pre-filter, and that improved it significantly, but I still have bubbles. Bubbles in the lines from the pre-heater to the strainer/pre-filter, and bubbles in the line from the strainer/pre-filter to the fuel pump on the side of the IP. I don't see any bubbles on the pressure side of the pump, though. I've checked the connections at the pre-filter and even replaced the line from the pre-filter to the fuel pump without improvement. Is the pre-heater prone to leakage?

So, I think I've got one or two, or perhaps even three problems. 1. air leakage into the fuel system. 2. low power and, possibly related, 3. TPS problems and issues with the tranny not downshifting.

Anyone have any insight into this?

Thanks in advance!

Regards,
Ben Pender
Madison, AL

[loubapache]

Welcome to the forum, Ben. Just a couple thoughts.

The sensor could be faulty so cleaning the contacts may not help.

Just a few days ago, a person with similar setup (although in a 1995 E300D) showed a picture of an apparently damaged cable for the kickdown solenoid. So I would take a look at that. Here is the thread (picture).

http://www.benzworld.org/forums/w210...on-sensor.html

[Kajtek1]

You don't have throttle on this engine.
The code is for Pedal Position Sensor what is the oversize potentiometer next to master cylinder. I had to replace it on the same model and it retails close to $500. Duval gave me better price but still OUCH.
With bad potentiometer the engine goes into safe mode, what limits the output.
Tons of topics on replacing clear tubings on those engines. Search the forum for them and welcome to the forum.

[gradyg3]

I had the same code being thrown as well. THere are three EGR related issues that can result in this code being thrown. If you look on your exhaust manifold, there is a small vacuum tube that runs from a little pipe outlet to an electronic circuit that is hooked up with the TPS. This is a likele culprit if clogged or damaged. If your exhaust manifold has not been taken off and cleaned adn you have a car with the EGR still in its original configuration then I can guarantee your intake manifold and cross over pipe are clogged up resulting in this code and poor performance. There is also a vacuum tube under your cross over valve that operates a resonator flap as well as a vaccum tube that runs from your EGR valve. But the code is most likely due to the little vacuum tube coming off your intake manifold. Good luck, try this 25 cent fix first before ordering a $500 TPS that is most likely fine.