Audi 80 tdi juddering bucking jerking

[avanttdi]

hi guys, as the creator of this thread its good to see so many people trying to help, and also to know that other people are having the same problem tracing the problem.

anyway heres an update

i have been driving my car around for a while now with the speedo unplugged to stop it juddering and as mentioned before this seems to make it driveable, although sometimes (it may be in my imagination) i think i car feel the car juddering very very slightly. however if i plug the vss back in, the problem is exaggerated tenfold.

the vss signal is used for an engine management subfunction known as active cirge damping. this function uses several other sensors and is designed to smooth driver input and reduce sudden jolts of torque in the drivetrain.

now i have been giving this some thought, and i have decided that the rough idling is indeed related to the juddering problem. The engine management system uses the crank sensor to maintain idle between set parameters......the link here is that this same sensor is also factored into active surge damping.

My thoughts now, and my plan of action is to try unplugging the crank sensor as this engine management system does not actually need it to run. I know it will go into a mild stage of limp home mode as it will use the needle lift sensor as a substitute signal for engine rpm.

ill let you all know how i get on .
also i may try scoping various signals at the ecu to check them for noise.

[midskev]

hi
im with you on that ava its got to be electrical funny but yesterday it was a wet day very humid the car ran far better than normal even started better and its always been a great starter, let us know if it works i still got to get a torx set to do the throttol petentiomiter im like you determined to sort it out lolol but slowly going grey lolol

keep up the good work

[Obsidian]

lo there ini, thnx for the interest btw, sorry buti can't post vagcom stuff, not sure what that means so have no idea where to get the readings you require. Yes, fuel injectors where cleaned recently, by a deisel specialist used by Audi Lincoln. Not convinced of his efficacy since he broke my accelerator pedal and cable-tied it back together and blocked the EGR valve vac feed with a ball bearing, for what purpose the almighty knows.

Needless to say i'm now going to try and fix this myself, the clutch is a new one and there's no loose bolts or mounts.

NOTE: don't bother with the throttle potentiometer, i removed mine and disconnected it, there's a six pin plug near to it that feeds it. the idle speed increases to factory default emergency throttle, but the hunting still continued! it ain't the throttle gadget!

[ini]

These 'case relief valve' threads may be useful:

http://forums.tdiclub.com/showthread.php?t=107803

http://forums.tdiclub.com/showthread.php?t=179625

[Obsidian]

thnx again Ini, nice post there, worrying and interesting at the same time. I dunno if i can risk trying to remove that device, i don't know if i can get the pump off on my own never mind try to take it apart. That may be a bit beyond me. And it doesn't seem to stay fixed for very long either! hmmmm, may be as well to get a new pump, are they a direct swap or need setting up?

[hawkeye1975]

Helllo juddererrreerrs,

My 1993 1.9tdi, hasn't got a rough idle, judders at low rpms and temp cuts out for a split sec, all randomly, whether hot or cold, admitedly, more so when warm. even so, still very random.

First thought was water in the fuel, then thought air in the fuel, as i seem to have air bubbles in the fuel line going to the pump.

Pos throttle sensor (bloody electrics, on an oil burner!!) or timing belt.

I would have thought though, if the timing belt tension is slack, and the teeth are jumping, that this would kill the engine ??

As my idle is fine, and most of the time the car runs fine, no leaks or odd noises, (apart from the driver cursing audi when it "cuts out") i wouldn't have thought timing ??

Driving me round the bloody bend !!

[Obsidian]

Lo ther Hawkeye, i don't think it's yer timing belt m8, if it had jumped over a tooth or two, then your pistons could strike the valves, and yes, that would kill yer engine. Not sure as you've got exactly the same symptoms as myself, since it ticks-over ok, but, i had Audi replace my timing belt and tensioner, it made no difference whatsoever. I can't suggest much at the moment, but it's not the throttle potentiometer (positioner), I'm pretty certain of that.

I think there was a post about air bubbles in fuel lines, but i can't remember what was said, something about a fuel filter. I've replaced mine several times and it never helps.

[hawkeye1975]

Thanks Obsidian,

This really is ridiculous, you would have thought Audi would come up with an answer here!.

Well, this is what happens when you put bloody electrcal boxs on good old oil burners !!

Keep up the good work everyone, glad i found this forum!!

[allan_audi]

This problem has had me stumped for months, but the VSS (Speed sensor) leads have really helped.

I have had shudder at idle but this can be tweaked with VAG-COM TDi timing checker and/or physical pump timing.

The main problem has been the quite bad jerk/shudder at low loads which will only dissappear when breaking the drive (clutch) or powering through. I've tried everything to stop this, engine mounts, MAF, N75 Valve, Cleaning Inlet Manifold, blanked off EGR, altered timing (physical and software) with no effect on this problem what so ever!

I finally got round to removing the dash fuse, then bingo all fine! Apart from obviously no dash. If you remove pin 43 from the ECM you get the same result, except you have the CEL flashing, I assume because loss of speed signal, but the speedo works ok. Pin 43 goes to pin 18 (on the blue dash connector behind dash), I assume the speed sensor feeds the dash which conditions the signal for pin 43 of the ECM.

My next step is to scope the signal, I have two wires hanging down behind the glove box at the moment so I can dis/re connect the wires when I need to, and also connect a scope.

Now, what does the dash do with the speed signal, I don't know yet, but I wonder if its a problem with the dash or whether we have some control loop problem as the cars are getting older. I've read that the ECM monitors vehicle speed to determine acceleration or deceleration.

It drives beautifully with pin 43 disconnected and you have all the dash functions, even the speedo working, I've removed the CEL bulb, while I'm investigating, but I'm determined to find the problem.

Anybody else have any more info??

[ini]

Has everyone already tried replacing the engine bay/ECU power 'relay 109' to try and cure the problem?

The 'old' version is a known bad component on early TDI's.

If the relay is physically damaged/weak, the low revs vibration could possibly cause a regular intermittent sensor & ECU failure, which vanishes at smoother/higher rpm?

Just an idea, but it is a cheap component to replace (with the new stronger type)