TPS gone bad AGAIN??????

[Angelos]

Greetings.
I'll get straight to the juicy part:
4-5 months ago I noticed that my truck would momentarily lose power and flash the 'Check Engine' warning light. This always happened at a very specific position of the throttle pedal. The diagnostic tool at the shop showed us a faulty TPS so I said ok and had it changed for a quite hefty amount.
2 months later, when all was looking ok I started hearing humming noises when running at ~1500 RPM. My mechanic was really baffled by this and said I should monitor it and see if it got louder or happened on any other RPM range too. Now, at the same RPM (~1500), hence at a specific pedal position for a specific gear, I get the same power loss and check engine ligh, without the humming !! I'm not 100% sure, but I think that when I hear the humming there's no power loss and vice versa.
Is my TPS fialing again??? or is it something else dying ? Could it be some sort of electrical short somewhere electrocuting the TPS and God knows what else???
I'm getting really worried about this, especially when I cannot keep a constant speed in traffic.....

 

[joey]

Fuel pump is going bad.... I would change it before it leaves you stranded.... Not sure if a D1 or D2, but if D1 when is the last time you changed the fuel filter? Either way fuel pump.

 

[Angelos]

joey, thanks for the heads-up. Truck is a '96 D1 Tdi 120K Km on the clock.
I think the fuel pump was changed 3 years ago by the previous owner but I'll have it checked on Monday.

 

[Angelos]

ok guys I'm getting a bit desperate here:
Went to the garage today, diagnostic tool was reading 'Throttle potentiometer bla bla, major fault'....
When in neutral everything was fine. In drive, the truck was losing power at around 1000~1500 rpm, also did this while in drive and pushing in the brakes (which in my mind should be the same as driving around right?).
we exchanged the TPS for another one, put the truck in drive and tried it by hand while pushing on the brake - everything run fine.
So we decided to install it properly and give it a try.
As soon as we were done... The problem came back !!!!!!
I'm really baffled here.... the diagnostic tool was insisting on TPS fault....

 

[joey]

Ok, TDI correct me if I am wrong.... isn't that drive by wire for the fuel? If so, and the diagnostic tool keeps saying TPS, yet when you change it your getting the same error, I would think either bad wiring or possibly corroded connector....

Just to let you know, not many TDI's in the States, so I haven't heard or read up on them that much.

Call another Landy shop and get a second opinion.

 

[Angelos]

Joey, thanks again for all the help.
The mechanic finally found a switch which was under the rubber cover on the top of the engine ( ...he couldnt tell me the name and I couldnt find it either, but I saw the part ...) and it runs ok...although I must say I'm not very confident that it'll stay like that for very long.
I'll monitor it and see how it goes.

 

[LRWheelman]

Inertia switch? just wonderin'. LRW

 

[Angelos]

Nope. Definitely not. I'll look it up in my Haynes manual and let you guys know. I'm pretty curious myself too...