Thread: Surging idle 300 tdi, help.

how are you fuel filters and lift pump?

Both replaced not long before I bought it apparently, I'm looking at doing a fauset lift pump install soon.

have you checked the fuel water seperator?

In addition to the above......

This also can be caused by faulty alternator - check for wear/stickiness on inside ribbed surface of "fan" belt, also check lights for "surging/pulsing" in brightness at night at driving speed. Also, you can check the alt voltage output if you have a multimeter.

If it occurs in a motor car with a rev counter this will probably show it.

When this happened to my D1 the alternator had regularly varying output from 12v to 16v to 0v.

OP,
surging is not terribly common with a definitve diagnostic pattern like "front end wobbles after hitting a pothole".

As Dave was intimating, it is most likely a fuel supply issue.

Are you doing the leg work on this one or taking it to a greaser and want some upfront ideas?

If was presented with this problem;

-Start at the Injection Pump and Lift Pump - check for obvious leaks while running
-Now back to the fuel tank, follow lines from tank to the water seperator inside the chassis rail. Remove entire seperator and clean out the gunk. With low pressure air blow back the supply line into the tank.
-follow lines forward checking for chaff or slight leaks (a small leak in a line may still supply adequate fuel but may suck air and cause a stagger)
-Lift pump on block, now this little guy can take a crap and you not even know it, but if there is any diesel at the weep hole, or the lever has little/no resistance, or you are going to start changing parts this would be my first guess. Only buy a 'Delphi' pump the rest are junk. Also blow the fuel lines from the lift pump back to the water seperator if you found mega gunge in the seperator.
-I would change out the fuel filter ("not long before I bought it" could be any length of time really)

If there were no visible leaks, the water seperator was clean and lines clean, a new fuel filter and then a new Delphi lift pump AND it still made the staggers (excluding some other funk like 87County dragging alternator bearing) well then it is either internal to the injection pump or one/ multiple injectors playing up (which they generally dont).

The Bosch pumps are generally pretty good, like Dave id be guessing you will find gunge in your fuel system or a slight air leak or the lift pump playing hookey?

Steve

Sweet something I can work with, I have had the injector pump rebuilt so I'm glad it's not that, I'll start with the water separator as soon as the wheather calms down a bit.
I'll let you guys know.
Thanks again for the heads up.