86 4kq, idle problem (long)

[Shaggs1996 at aol.com]

Problem started a few days ago.  Im gonna explain this the best I can, so 
bear with me.  Went to go run errands, started car, car ran rough, 200rpm, didnt 
stall, but when given a decent amout of gas, car sounded like it was 
backfiring (loud "boom" from engine bay).  After feathering the gas a bit, the idle 
evened out to 1000rpm, and I was on my way.  Same thing happened twice later that 
day after coming out of a store and getting gas.  Later the same day, after 
the car sat for a while, I started it up and everything was merry, drove off, 
car ran great.  Get to friends house, shut down, come back 2 hours later, car 
stars awesome, and drives off great.  A few mins into the trip, car loses 
power, and wants to idle at 200rpm again.  Im forced to pull over, and rescure the 
idle via my foot, again.  If I try and move the car when the idle is that low, 
the car of course doesnt wanna go, and lunges forward as the revs drop.  Car 
gets going, and gets home fine.  I had time to look at it tonight, so after a 
stuck ebrake, I pull the car into the garage.  Check some O2 sensor wiring, 
pull the plugs, and check for vac leaks..nothing, everything there checks out.  
Fuel filters are a month old, fuel pump wiring is nice and dry, but there is 
alot of ice under the car, and around the fuel lines.  I did pour in some fuel 
injector cleaner tonight as well.
Thats where I stand now.  Car does run right when it wants to, and this 
problem is sporatic!   Any ideas where to start here?  Ive asked around alot, but 
havnt consulted my Audi tech friend yet...help!

Mike 
85 4k 
86 4kq