Audi 80 Cabrolet

[LAW2]

Please can someone help me?

I have a 1998 model as described above, 1896cc Ti. Up until tree weeks ago was brilliant but then suddenly no revs passed 3200.

It is an intermittent problem, as soon as ignition is turn OFF and back on.......it seems okay for a short while............then dies back to stick at no more that 3200.

Have change air mass meter and electro-solenoid valve, as defined 'defective' by AUDI, but no change to problem indicated.

Thanks for any help,

Law

[A6_25TDI]

I have the same problem on my 2.5 TDI. It seems that the turbo bypass valve blocks open, effectively reducing the boost pressure, which leads to the revs not going higher than 2000-2500. This is intermittent, sometimes it blocks, sometimes not. The valve seems OK, the vacuum that commands it is also good. Changed the airflow meter, now the car runs better, but I still get the valve blocked, though not so often.

Currently I believe that the ECU commands the valve open on purpose, due to some other conditions it senses. I am now looking to see if the exhaust system is restricted somehow. Maybe the catalyst is clogged, I'm going to clean it, though I don't know how.

I'll post some updates if I find anything.

P.S. I also noticed that if I turn the ignition off and then back on, this behaviour disappears, but not for long.

[A6_25TDI]

Cleaned the catalyst and no success. Car runs the same.

I also noticed another thing about my car, which I am now wondering if it's connected to the power loss. The engine temperature stay at 78 degrees Celsius most of the time. It only reaches 90 degrees when the car is driven very, very hard - e.g. pedal to the metal from 0 to 180 km/h (5th gear).

Moreover, I measured some values while driving like that, and the maximum boost I get is 1600 mbar, in 5th at 4000+ rpms, while the air flow is 650 mg. This is at 170 - 180 km/h. In all other gears, it does not get so high. I should get 2000 mbar and over 1000 mg in 3rd at 3000 rpms, that's what I am told.

Are the power loss and the strange low engine temperature maybe connected?

I am thinking of checking the injection timing next. I'll post updates.

[SimplyAudi]

I am very interested in how successful you have been in solving your problem, I have the same problem on an Audi 80....low temperature, and not revving past 3000.

[A6_25TDI]

Well, no luck yet. 2 of my camshafts had broken, so I had no time to address the other issues. Just bought a used cylinder head with valves and camshafts from a junk yard today. Looking forward to put it on the engine. Figures so far are 650 euros plus I lost my mobile phone in the rush I'll have to pay my mechanic, so that's probably some 50 more euros.

Anyways, I had done some readings on the net (plenty of spare time with no car ) and just found out that these symptoms (rev limitting, reset by ignition off) may be caused by the engine ecu entering 'limp mode'. This seems to be a protective mode into which the electronic switches when some parameters are outside some 'control limits', in order to protect the engine from potential damage.

Now, in my case, I also get the following fault: "Intake manifold pressure - control limit not reached" which matches the overall feeling that the turbo is not working at normal boost and the vag-com displayed low values of boost pressure. It might be possible that upon detecting the low manifold pressure, the electronic puts the car into limp mode which limits revs, torque and power.

What I'll have to check more seriously than before is:
1. Intake manifold leaks
2. N75 unit (controls the turbo bypass valve)
3. turbo bypass valve

And after these, of course, injection timing. Hope somebody will tell me the timing advance specs.