71 xr7 idles real rough, especially in drive sitting still, noticed when i parked it and left it running the sounds like idle is bad and noticed black smoke coming from tailpipes. Also whenever coming to a stop sounds like it wants to die. Could this be a timing issue? Also my tank is full of crud so when I get down to a 1/4 tank it acts weird, gas level was just about 1/4 tank when I noticed all this. I tired of feeling like this car is going to break down on me any day, Im about to just take it to a mechanic, but I have yet to have a good experience with any mechanic. Last time I took her to have a tune up instead of doing it myself they tried to charge me $300!!! just to change the plugs. Of course I can and will do any work myself, but I cannot figure out what the deal is with this car. It is my everyday driver and I feel like Im about to loose her. Any help would be great, I can take pictures/ videos and post if that would help. I love this car and do not want anything else! PLease help! Its like a girlfriend that Im on the verge of loosing! lol ahahahahha really though, I need some expertise on this! I know theres someone on here whos very educated on these cars and trouble shooting issues.