Thanks for taking a minute to read - I have searched, perhaps poorly, and find similar issues, but most of the resolutions have been tried and failed.
I have a 1993 VW Cabriolet - Mk1 style, NOT Cabrio - with about 97K miles on it. Really good shape overall, and seems like a good first car for my daughter to putter around town in - even though it has that god-awful old 3 speed automatic in it. I had an 80 Rabbit and 80 Scirocco when I was a kid, and they were great back in the day when I had em (mid 80s).
It has this weird issue whereby it runs fantastically for about 30 minutes at idle, or 45-60 minutes at speed, then starts to sputter, blow smoke and lose all throttle response. Let it sit for a couple of hours, and it will fire right back up and do the whole cycle again. Seems to me like it might be some vacuum leak, but I cannot find it. Below are the many things I have done (or had done by mechanics) to this machine - the bold ones being things I felt pertinent to the issue:
--Exhaust, manifold through cat
--new brake booster, water pump, timing belt,
--new distributor cap
--changed oil and filter
--new air filter
--new washer pump
--fixed washer stalk switch
--new washer fluid hose
--fixed wayward headlight
--replaced radiator fluid resevoir cap (which was missing valve, so coolant would blow out of it as soon as everything got hot )
--replaced fuel cap
--fixed various interior bits
--fixed AC control lever (was out of track) -- still needs recharged
--replaced AC relay
--replaced thermostat, gasket and housing
--replaced blue coolant temperature sensor
New ICM and timing belt definitely made it run much better (when it does). I am thinking my next step may be the fuel pressure regulator, but was wondering if anyone had the same issue that they eventually found and fixed. I have no whining from the fuel tanks area, and fuel seems to be moving initially fine, so I dont think its the pumps. Thought it was the coolant and overheating, so I replaced the sensor and the thermostat. Doesn't seem like its that now..
This is definitely something I did not ever deal with on my old VWs, even though much of it is familiar to my days of repairing those critters.
Thanks much all.