i have purchased a 91 80 quattro and it starts rough and idles rough now that i have played w/ it in the driveway for a little while this afternoon? any ideas!!

 

The biggest problem with older cars is corrosion and oxidation on many of the contacts. Then check the vacuum hoses often they either fall out due to being hard and cracked or soft and spongy from oil contamination. Check the nylon hoses as well, these have a tendency to crack from whipping or they rub through. The ISV valve has a tendency to stick or gum up. A bad injector can give rough idle.

 

I had similar symptoms. I tested my injectors just by letting the car idle, then starting with the closest injector to me, I pulled the wire connector off for about 8 seconds and then reconnected. After going over it a couple times I knew it was the first, or closest injector to the front of the car because it made no difference in the idle when disconnected. If the injector is working, when you disconnect it the car will idle worse...