I have a 1994 Dodge 250 van. At first it had a slight vibration like a tire going flat but all were good. Then it had a loss of power and backfire, possibly through the intake. It's slowly getting worse. First time it happened 90 miles from home, now it does it after a mile. We changed out Oxygen sensor, Ignition coil, had the whole thing looked at by mechanic (who found nothing wrong), plugs and wires are all good. The cat would never get hot so we don't really think thats an issue. Can't see any vac lines off or any lose wires, Transmission is good. Van will start and idle great. We thought it might have a correlation with the thermostat opening but it might have just been timing of going to crap. The fuel gauge don't work so cant really tell if it's using more fuel than normal. Exhaust don't smell rich or lean. The only code we can get from it is 12. We're at a total loss of what it could be without putting enough money in it to buy another vehicle! Thanks.

 

Plenum gasket?

http://www.hughesengines.com/Index/p...p?partid=27091

 

Can you look down the inside of your throttle body and see if you have a pool of oil inside your intake manifold?