I have a 99 Dodge Stratus 4 cyl 2.4L, automatic.
It has been idling rough for a few months now. It feels just like it is misfiring. Tach confirms quick dip in rpm then return to normal idle. It has never actually stalled, just a quick rpm dip and subsequent shuddering, then recovers for a few seconds.
Also runs very rough, at 47-48 mph under light “cruising” load. Sounds crazy, but it does (did, see below) not happen at 45 or 50, just in the 47-48 mph range. Again, it feels like bad misfiring, with the car losing a lot of power and shuddering until I accelerate/decelerate away from this speed range.
NOW, over the last few days, the rough riding has gotten a lot worse, and occurs at all speeds. It is worse under load (mild acceleration, hills). Still feels like misfiring. Loss of power makes it hard to maintain speed up hills, at any speed. Also, today for the first time in its life the car backfired while trying to accelerate up a hill from a stop, at a speed of about 15 mph.
When idling, I can occasionally smell gas.
So, the coils are 2 years old, spark plug wires are 2 years old, spark plugs are 2 weeks old and air filter is 4 days old. Check engine light is NOT on and there are no error codes as of yesterday. Fluids are all good, except I am about the kick the stupid thing until it bleeds.
Guy at parts store suggested Idle Air Control Valve, but I am dubious, as this now happens at all speeds.