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Discussion Starter #1
I have tried to get this resolved elsewhere without success.
My 1998 Avant TDI was running ok but a bit lumpy when you put the revs at about 1800 - they would waver.
I disconnected the MAF sensor plug and the problems started. There was no difference in the idling so i replaced the plug. The next morning the car was in limp mode when i started (or maybe a split second after i started it)
It jumps/jerks into gear and will not rev or drive over 40 mph etc.

It could be reset after leaving the ignition on for a few minutes then it would be ok until next morning.
It got worse so i booked in to VW and they reset the ECU etc and it drove all day no problem.
Next morning back in limp mode. Took it back and they reset again. One code which i dont know but he thought it was the pump pressure or something.
It drove ok again til next morning.

I failed to get it out of limp mode after several times resetting myself.

A gearbox specialist said the MAF sensor tells the gearbox and pump what speed etc the car is going so a bad sensor would make the gearbox jump into gear if it was faulty. (this is from standstill not driving)

I just found a damaged vacuum hose off the inlet manifold system - it goes under the water reservoir and have fixed this but it is still in limp and i cant reset now.

VW want to replace the ECU or pump (easy option but no guarantees of course) but i think it is related to me messing with the MAF plug. It drove great when reset by VAGCOM)
What should i do? Can i check the cabling on the MAF sensor to check it is ok?

Many thanks
 

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Is it an auto?

Forget the ecu or pump unless they agree to not charge you if it doesn't fix it. Check ALL the vacuum lines ALL the way. You already found one.

If you have a vag com, check the MAF sensor readings and see how requested vs. actual are. If they're way off you found your problem.
 

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Discussion Starter #3
I connected a new vagcom and pulled these codes

3 faults
00550 - start of injection
17-10 control difference intermittent

Engine

00523 Shareware version required etc.
00553 Register to activate

Trans (auto)

18625 - Load signal error message from ECU
P1857-35-10 Intermittent


I read somewhere that 550 is the MAF readings ?? This would tie up with my intial messing about with MAF connector so maybe i trashed a wire?

Also noticed large bubbles in fuel line although car has been standing for a while now.

Thanks for any views on these readings
 

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The first code is injection pump timing. Try checking the injection pump timing. I don't know what engine you have but you have to use the chart in your service manual for your engine. Some charts for ALH engine are in the timing belt writeup part 2. There are also charts in the ross tech software that show up in basic settings.

It seems like the second is telling you to register the shareware version :) This is where they make their money. You could go to an auto parts store and see if they'll scan it and check the injection pump timing.

P1857 is error code has been stored. I had to look it up and it just says that it means the engine light has been illuminated. Not sure exactly what it means but it could be relay 109. This is a relay that controls power to the ecu. It normally causes sudden engine stalling but it's possible it's causing your problem. Look under the dashboard next to the steering column. There is a relay panel. If relay 109 is black, replace it with the new gray relay.
 

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Discussion Starter #5
It is a 2.5TDI
Audi independent also came up with pump timing and adjusted to try and see if that had any effect. It didn't. When he cleared the code the car was 100% but only went into limp on the cold morning start.
That says to me the mechanicals are ok but a sensor is causing early morning cold start fault.
The clues are here i just don't know what they are telling me and it seems the specialist is no help either.
If the pump was faulty the car would not run would it?
Can the MAF sensor provide incorrect info at cold startup and upset the pump?

Can i check the MAF wiring for damage with a meter?
 

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Tt's possible that was what they were talking about the cold start advance solenoid. This advances injection timing on cold starts. I think it throws a code though but not 100% sure. It is user serviceable.

A faulty pump can still run.

Not sure which MAF you use but it's probably a hot film type. To see if it's bad you must use a vag com (VCDS) and chart/log requested maf vs. actual maf. More details in the MAF troubleshooting article.
 

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Before you start chasing pump problems, you've double checked all the vacuum lines? Bad coolant temp sensor?

Those codes showed up after you cleared the old codes?
 
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