High idle and loss of power

Hello All,

Name is Jon, I am an owner of a 1985 110 2.5 na. I recently changed out the fuel filter and had a new lift pump put in. Cold start no problem and warms up no problem.
The problem is when I am driving and get to about 40-50mph the idle increases and I feel the motor starts to lose power...like it isn’t getting fuel. Once I get it started with a few cranks. It’s starts with a high idle and eventually dies again.

I have checked for leaks air and diesel, but there isn’t any. Please help...been working through this problem for 2 weeks now.

Have you changed the air and fuel filters?
You might as well do the oil filter whilst you are at it.
The 2.5 NA is as simple as they come, so if you give us a clue where you are, there might be someone nearby who knows these engines.
Welcome to the asylum.

Yes, changed air and fuel filters. Took it to a garage whilst the lift pump was faulty and replaced, but I am still getting the high idle. It starts good and idles normal...once I start to drive it and get it up to 40-50mph it starts to act like it’s not getting fuel, starts to idle high and eventually motor stops.

I am in the Mildenhall area.

jonnysay said:

Yes, changed air and fuel filters. Took it to a garage whilst the lift pump was faulty and replaced, but I am still getting the high idle. It starts good and idles normal...once I start to drive it and get it up to 40-50mph it starts to act like it’s not getting fuel, starts to idle high and eventually motor stops.

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How do you mean idle high? The engine isn't idling when you are doing 40-50mph? Does your model have a sedimenter in the fuel line? I think they are near the tank.

Are you losing any water?
What colour is your exhaust?
Have all the pipe connections been nipped up?
It sounds as though whatever happens happens when the engine is warm, which could indicate that as ne or more metal components expand it allows either air and/or water into the pre-injector fuel system.
Does the run off pipe have any kinks in it and free flows either back to the fuel filter or the tank?
IIRC sedimenters were fitted as an option on post '87 Fenders and TDi's.

Al2O3 said:

How do you mean idle high? The engine isn't idling when you are doing 40-50mph? Does your model have a sedimenter in the fuel line? I think they are near the tank.

Click to expand...

When I start to notice the change I take it out of gear.

Oldseadog said:

Are you losing any water?
What colour is your exhaust?
Have all the pipe connections been nipped up?
It sounds as though whatever happens happens when the engine is warm, which could indicate that as ne or more metal components expand it allows either air and/or water into the pre-injector fuel system.
Does the run off pipe have any kinks in it and free flows either back to the fuel filter or the tank?
IIRC sedimenters were fitted as an option on post '87 Fenders and TDi's.

Click to expand...

When the idle is running high I notice a very thin white colour of smoke. No kinks or water leaks. And yes, it happens when the motor is warm.

White tends to indicate that there is water (irrespective of the amount) getting into the cylinder(s) rom somewhere.
Might I suggest that before you next take her out, slacken the rad cap, so that it sits there but doesn't seal or pressurise the cooling system and see what happens.
You can't do any damage, so don't worry!
Then come back and let us know a/. if you have lost any coolant, and b/. if the problem persists.

Haven’t tried it yet, but did notice that a bolt on the lift pump was loose.
Curious, does a lift pump suck air too? I was feeling around while the truck was on and I feel a small hole on the bottom sucking air.

Hold on, just found a diagram...it is a weeping hole.