Could this be a lambda issue?

blocked cat would be my first thought

On full throttle most cars go open loop so the lambda sensor no longer controls the mixture.

It did have a new cat I think about 2 year ago. If I remember it snapped at the joint where it connects to the exhaust so had to replace the whole cat section, although I suppose even a newish cat can break up. It goes for an MoT later this month so will get the garage have a good poke about see if they can see anything. Not sure if this is also relevant but it idles ok with no lumpiness but I notice that if you try and hold the revs at a steady fast idle it fluctuates up & down slightly.

Has it got an air flow meter? Is it stuck?

I guess that would rule out the lambda then. It does seem fuel related though and if you ease off the throttle you can feel it become more responsive.

Hmmm Is there a full/wide open throttle switch on it? What sensors are on the throttle body since I am thinking two. I suspect that after you ruled out the cat. If the full/wide open throttle switch is not functioning then maybe the 02 sensor is not cutting out and allowing full power.

Again I am not familiar with the '93 Audi 80's there. Of course I ASSuME that you check for any obstructions in the air intake system. I have seen nests inside of air cleaner boxes along with leaves restricting air flow. ;-)

JMHO

How old's the fuel & air filter?

Worn fuel pump giving low pressure at WOT?

Does it get an italian tuneup every so often?

That was my thought- maybe a MAP sensor of a MAF or whatever it uses to measure airflow in. I'm not familiar with the setup on this engine though.

It's got one. The normal plug it into Vag-Com applies butodds are it's an air or fuel flow restriction.

Blocked cat / exhaust is mine. NOT Lambda sensor.

Or cam timing incorrect.

Tim.

Thanks for the replies, it does sound like a fuelling problem. I'll get hold of a fuel pressure gauge and check the correct pressure is reaching the injection unit. Autodata says to manually trigger the pump and reading should be between 0.8 & 1.2 bar and hold at 0.5 bar after 5 mins. Should at least rule out any filter, blockage or pump probs. It's got good pick up if, for e.g, I knock it into 2nd gear to turn into a side road with a steep incline. As soon as I press the throttle it will pull very well up hill from low speed but get to a certain point and nothing much happens at the top end of the throttle range.

The fuel pressure effects the entire engine range. If it were wrong it wouldn't idle properly either. I suppose a blocked filter could have more effect at high demand, though.

The range of 0.8 - 1.2 bar seems awfully wide to me - on mine a couple of PSI makes a big difference. Although of course the pressure does change depending on engine vacuum. But I'd expect the static pressure to be much more accurate than that.

Yup, if the filters clogged they're fine at low demand & bad at full bore.

Indeed. My old SD1 runs at 36 psi - and most modern vehicles are higher.

Got a fuel filter ordered for tomorrow. I'm assured it's had all filters changed at every yearly service, but with the fuel filter hidden away under the back end somewhere I will make sure & fit a new one anyway. The 1 bar figure is the regulated pressure when measured with the gauge fitted inline between the fuel inlet pipe & the injection unit - if that sounds more feasible.

One Bar is about right for a SPI system. They run much lower than MPI.

Graham

Didn't realise Audi ever used a SPI system - although the OP did say so.

I'd thrash the hell out of it for a while and see if it picks up...