1986 golf troubles

I have recently inherited a late '86 early 87' vw golf. It ran fine last year then the clutch bracket shattered so it sat all winter until i could afford to get it fixed. It ran perfect before i parked it for the winter. Then, i got it fixed and there are a few problems with it. The most major problem is the engine is running very rough. The sparks are fowling very quickly. The car stalls constantly. There is a great loss in power also. there has been many hills i havn't been able to make it up. At first i thought that maybe i had a dead cylinder, but it appears they are all firing. I have no clue what the problem might be. I don't know if its connected but there is also another engine problem. if i keep it at 2,000 rpms steady it cuts back to around 1000 and then back up to 2000 and back down and it will do it all day if i keep the pedal in place. but, if i keep it above or below that level it doesn;t do it or if i give it gas through that speed it wont do it. Any help with these problems would be greatly appreciated.

CIS fuel problems can be very difficult to figure out, and diagnosis can require specialized equipment. It seems to be running rich, a simple first place to look is at the coolant temp sensor. It's a two pin sensor located on the cylinder head water flange where the upper radiator hose meets the head. Resistance across the sensor should be around 2000-3000 Ohms @ 68 F and steadily decrease to around 200-300 Ohms @ operating temperature.

seems to be mixture related,look at the carb mounting,is it split?test by starting engine and try moving carb,if engine speed increases/decreases,suspect mount.otherwise make sure all earths are secure.esp,at carb.

Thank you for trying to help me. I appreciate it. I tested the sensor with an ohm meter. The sensor its at the correct ohmage. Any toher help would be greatly appreciated.

How old is the gas?

the gas is fairly new. If it helps, i accidently filled up with diesel a few tanks ago. I dont know if that would have a effect on anything.

How much & how long has it been run since? How did you get it out? Does the car put out grey exhaust smoke? Have you cleaned the plugs since this incident?

Whatever is coming out of the exhaust it won't matter much.

Get the entire system flushed, and then put a complete fresh tank of fuel in. Run the car through this entire tank and that should coat all of the relevant parts again.