Rough idle
 

My 86 420 idles really rough. It is also intermittent. Sometimes it will be smooth, and sometimes not. I tried fuel injector cleaner gas additive and it seemed to help at first, but then it would go right back to idling rough even when I am still using the stuff. Is this an ignition problem? A fuel system problem? Thanks for any help.

Has this car been jump started lately?? if so check the OVP relay. Also check for vacuum leaks. Try these two and report back