Audi 100 C4 Losing all power while driving

[100problems]

Hi there,
I drive a 1994 Audi 100 C4 2.0E (ABK engine) and have been learning about it (fixing it) since I got it.
The most recent and current problem came while trying to fix a misfire. The misfire was intermittent and only seemed to be present while the engine was hot.
To solve this I changed a variety of things:
Leads
Plugs
Distrib Cap
Ignition Coil
Lambda Sensor
Cleaned out the injectors, fuel rail and plenum.
New fuel injector relay
New ECU Relay
New ECU
One of these last two solved the misfire (probably, it hasn't returned since those)

The new problem is that the engine loses power no matter where my foot is on the throttle at random times while driving along. The engine does not cut out but will not respond until I let it return to idle then give it some gas.It seems to happen most at night when the engine is coldest. Although i can persist for some time after the engine is up to temp. Very rarely happens in daytime.
It started after cleaning up the contacts on the old coil so I assumed the problem was routed there. But after fitting a new coil the issue persists.

If anyone has any ideas or has seen this problem before please let me know.
Thanks

[100problems]

Noticed the coolant was looking a murky brown colour, so I've flushed it and refilled it. Oil was pretty dark too for having been in only 6 months, so some fresh stuff has gone in.
A friend has advised me that the coolant temp sensors can play up a bit on these and to try swapping the wires on them round. I've done this and it hasn't produced any additional running problems. Yet to test it in the cold again though.

[wildbeeste]

I had a 100 which had lots of power and then no power as if only running on 2 cylinders. Ease off and lots of power but as revs rose power evaporated
it was a collapsing catalytic convertor
Solution - new exhaust

[100problems]

Thanks for the advice, new CAT ordered.
Here's hoping that's it.

[rowdy-999]

Fuel pump?

[100problems]

Also a possibility , but i'll wait and see if the cat works.
Cheers

[100problems]

Quick update -

Changed the cat and the issue seemed to go away, apart from one lone incident.
However, yesterday my car started losing battery power while driving, dash lights dimming, fuel and temp gauges not getting full readings etc. At the same time as all this I was getting the same loss of engine power.

Current guess is that the alternator is past it and cant keep enough power output to spark properly. Will update when I've changed the alternator.

[100problems]

Update -

Following the dramatic incident with loss of power (on quite a long drive up the A9) I took the alternator off. Took the back of it off and replaced the voltage regulator and brushes which fixed the barely being able to drive issue.
Once again I thought problem solved just a little too soon. Had another minor incident the other night with my foot on the floor and no revs coming up. Let it idle and revved it up and it's behaved since then.

Could be an issue with a bad grounding somewhere. Will crack out the multimeter again.

[100problems]

Additionally, I also now have a buzzing sound at certain rev bands. Not sure what it is, might be the new brushes wearing in.

[100problems]

Update -

The buzzing sound persists, but i have mostly drowned it out with a new exhaust....

It has become very clear that the misfire is electrical problem with a poor/ corroded connection or wire, since it only misfires in or shortly after the rain. Todays rainstorm saw me using my hazards quite often.

I have changed the ground strap but might need to clean the engine and body where it bolts on a little better.