Hi, new to the forum.  My local VW dealership had my car for over a week (did NOT charge me for hours of diagnostics) and their senior tech could not figure out the problem with my car.  

1992 Golf 1.8 - experienced problem just over a year ago.  Car would suddenly spit and sputter, fuel mileage would go down the tubes, acceleration would feel sluggish, black smoke would pour out of exhaust.  The problem would come and go, whenever it felt like it.  If I took my foot off the gas, then pressed again, I could accelerate, but problem would come back.  VW dealership said the O2 sensor was the problem, replaced it and it worked fine until this summer.  Battery died, replaced it and car still seemed to run fine.  Recently had seals changed on engine (valve and head gasket) and timing belt was changed.  I remember they had a hard time getting the timing set, as the distributor had seized.  They managed to get it loose though and set the timing properly.  The car seemed to run fine after the work, but then started up shortly after (a few days).  Had the entire muffler system replaced (including the cat).  The O2 sensor was replaced again, but the problem is still there.  The temp sensor was replaced, again, problem still there.  

Could this possibly be a bad MAF sensor and/or wiring issue?  I've read elsewhere online about people with similar problems but it seemed to be a lot of 1999 - 2002 models with a MAF failure issue.  Before I took it to the dealership, I unplugged the MAF to look at the connector for a minute then plugged it back in.  It drove great all the way to the dealership, no problem whatsoever.  It took them a few hours to get the problem to reoccur for them.  Could this be an indication of some fault with the wiring/MAF sensor and the ECM?  Could the ECM be resetting some code or problem?  There were no codes or anything that they could figure out.  

Any help with this problem would be greatly appreciated!  VERY frustrating.  

for the MAF, check for 5 volts between pin 4 (gnd) and pin 3 (+5V), pin 2 (output) should vary between 1V & 5V as engine rpm is increased, at 3000 rpm, approx 3V, hope this helps  

I had a 92 16v that had a spitting and sputtering problem.  The coolant temperature sensor had gone out.  IF this part doesn't work it will not tell the computer if it is at the correct operating temperature.  Typically if it thinks it is cold it will run rich till it has warmed up.  

The second problem i had that lead to such a case with the same car was a bad O2 sensor.  It looked fine till it was removed.  The wires at the top of the sensor had been broken thus making intermitent contact.  So sometimes it would get a signal and other time not.

good luck  

you might not be getting enough fuel presure, there is a can shape ( I forgot the name of it) under the car inline with the fuel line.  Change that see if it work, I use to have the same problem before