I'd check all vacuum lines. I got a recently purchased (back in September.) Dodge Aries and had a similar instance; when I first got the car, it worked GREAT, then 1 day it just would not start, I had to pump the gas to finally get it to start. Took it to the dealer and they found a great many of the vacuum lines were dry-rotten and cracked, resulting in many large vacuum leaks.I went through many months driving it like that though, thinking it was a gunked up fuel/pcv system, from sitting so long (2+ years.), So I threw anything I could buy into the tank and changed the oil many times, alternated Seafoam and MMO in the crankcase as well as the fuel tank, with no dice. Then that's when I decided to take it to the dealer and they revealed the underlying problem. Lol.
Once I got it running, and in gear, it drove GREEAT on the highway, no problems at all, other than the fact I was only getting like 150 gallons to a 14 gallon tank. Definitely was running rich, but it was not spoking black smoke or anything, but I had the heavy black soot on the tail pipe.
Monday, May 9th, 2011 AT 8:09 PM