I searched a bunch of old posts, but no one seems to have had the same problem. I've got an '85 Econoline, with a 300/AOD. The van starts fine, and runs great for the first few miles. Once the engine warms up, it develops a very rough idle. If I hammer it, it will accelerate fine, but as soon as I hit a low cruising rpm, or back off the gas, it goes back to running rough. Sometimes cruising or coasting down when it's running in this condition will make the van jerk back and forth. After a while of driving it will often smooth out and run almost normally, sometimes going back into the rough running condition later. When it's running rough, I notice a strong smell of hot engine oil that isn't there when it's running normally. I assumed this was a vacuum leak, but the carb cleaner trick didn't show me anything. The oil smell made me think it was PCV related, but the valve is new and the suction is strong on the line. I even tried pulling off the vacuum lines from the EGR and the solenoids at the rear of the engine individually and plugging the ends to see if it affected the idle (it didn't). The carb still seems to be bolted together OK, and I tried spraying around the base of the carb to check for leaks. Any one have any idea where else I can look? Please help me before this thing jerks and bucks me right off an icy road!

Thanks in advance!

 

check for stuck heat riser in exhaust system behind exhaust manifold, check cat converter may be plugged one of these two sound like the culprit?

 

Thanks for the input. I actually reamed out one cat and chopped the other one right out last week thinking that was the problem. It bought me a little more power around town, but didn't fix the problem. Are you talking about the "stovepipe" that goes to the air cleaner assembly, or something within the exhaust manifold?

 

usually it will be right behind the exhaust manifold between manifold and the start of the pipe.