A4 1.9tdi poor acceleration

**MACGREGOR** · 29-05-2009,12:14 AM

Hi Folks,

I've got a 1999 A4 1.9tdi avant, 122K on clock - bought recently & before that it's been sitting for a few months. There's good service history and it's been well cared for, however, ever since i've had it, the accecelaration is really poor (0-60mph in about 30 sec!!); otherwise it cruises along quite happily on the motorway, just takes a long time getting there! The previous owner assured me there was nothing wrong with the car and it is just because it was sitting for a while. The acceleration is worst in 1st to 3rd and won't go over 4000rpm. There are no warning lights on (except airbag) but I'm assuming it is in permanent limp mode? Am I correct? I've changed the fuel and air filters but to no avail. There is no smoke from the engine and it doesn't eat oil. Looking around other postings on the forum I assume the next step would be to look for a fault code? I notice cheap VAG fault scanners on ebay for around £20 - are they worthwhile or am I throwing my money away? Any advice on either code scanner or car would be much appreciated!

**johnwintle** · 29-05-2009,12:29 PM

Is the turbo working?
Sounds like it might be the MAF, which may not throw up a fault.
Do you have a VAG Specialist near you up in Scotland, or someone that might have access to VAG-COM? The codes may give you an indication of what is wrong but they may not give you the definitive answer, only another tool in the toolbox.

On another note, as this looks like a PD TDI engine fitted to your car (engine code will confirm), has the correct PD oil been used through out it's life. If not this will prematurely kill the engine...

**Ian_Martin** · 29-05-2009,12:57 PM

I have the exact same problem the exact same car, though mine has a nice 177k on the clock! I've read about this quite a lot on this forum but have yet to decide how to take this further so I'm interested to see how this thread develops. Also, I'm a complete lay in terms of car talk so if somebody could explain the acronyms MAF and VAG-COM I'd be pretty grateful!

Cheers

**johnwintle** · 29-05-2009,01:09 PM

MAF = Mass Air Flow which is the device that the engine computer uses to determine how much fuel should be injected into the engine against the engine revs, and the speed of the air being drawn into the car.

VAG-COM is a diagnostic computer program that emulates the official VW Group 1551(?) tool and is produced by Ross Tech in the USA. Is is used to read the fault codes that get generated, amongst other things.

**MACGREGOR** · 29-05-2009,04:05 PM

Many thanks John - will try to disconnect the MAF and see if this improves matters as a first step. It's an AFN engine code - oil has been changed every 10K or less using Castrol Magnatec which should do the job. Will try a compression test just in case. Apart from poor acceleration the engine runs and idles perfectly so I suspect premature wear is not the cause. All belts incl. timing were done 5K ago. There is an Audi specialist in Inverness but trying to avoid spending any money that I don't have to at this stage otherwise don't know anyone with VAG-COM up this way.

Will let you know if I have any success,

all the best

Greg.

**MACGREGOR** · 29-05-2009,04:10 PM

Forgot about turbo in the last reply - it feels like the turbo is not kicking in although seems to be OK at speed. Is there a definitive way to test for a duff turbo? The previous owner assured me the turbo was fine. As I said the revs seem to be limited to 3500 to 4000 at best so it makes me think this is something to so with the engine management system rather than the turbo.

Greg.

**MACGREGOR** · 29-05-2009,05:45 PM

John, you hit the nail on the head - I disconnected the MAF and my acceleration has returned! Is it safe to run it temporarily disconnected or will I damage the engine? Also, do you know what tool I need to remove the two screws that hold it on - they have torx heads but have got a raised bit in the middle making it impossible to turn with a regular torx driver? Finally, is it worth going for a cheaper pattern replacement or should I stick with the Audi MAF?

thanks

Greg.

**johnwintle** · 29-05-2009,07:41 PM

Going to depend on your budget really. The genuine one may be be available as an exchange which may effect the cost. I would think that the p/n of your MAF is something like 028 906 421 and this might be available with the X suffix at around £70 inc vat (old price). Best to check with Audi on the price before you commit to any others. Obviously check out the prices at Euro Car Parts and GSF online also.
Running without the MAF will make the engine run better for you in this instance, but it is not recomended for more than a short time.
Regarding the tool to release the MAF ask at ECP or GSF or search online.

John

HomerSimpson · 29-05-2009,08:50 PM

Hi Greg,
With regards to the MAF, you will probably find that when you get the new one it will be the complete unit, so no need to remove the tamperproof torx. It is a simple enough job to do, just remove the section of air inlet nearest the wing, disconnect the old MAF, remove the hose, remove the two 6mm bolts (10mm Spanner), remove the MAF unit (It pulls out towards the radiator) and hey presto. To put the new one in is a reversal of removal. Oh forgot to say about the heat shield

, this needs removing before you can remove the second bolt, but is only held on with 4 screws (Phillips).
Hope you find this helpful.

**Ian_Martin** · 30-05-2009,04:05 PM

Thanks for the useful information gents. I located the MAF (now I know what it is!) and after disconnecting it the performance certainly improved, the only problem being that my fuel gauge took on a life of it's own! At least I've now pinpointed the problem, I just need to decide whether to go for a replacement. The question being do I forgoe my 700 miles from a tank of diesel for the improved performance!

On the subject of replacing the unit, is this what I'm looking for, or is it the plug?