99 Stratus: Rough idle at first, and now always running rough

Maintenance/Repairs
1

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.

Suggestions?

Thanks!

2

Uneven RPM at idle – where the RPM briefly dips then returns to normal – or the RPM surges briefly, this can be due to air/fuel mixture problem. And since you say you notice a gasoline odor, that could be confirming of this. Mixture problems are most often caused by air leaks. Air is some way or another bypassing the MAF, so it isn’t properly metered. You can take a look at the vacuum hoses, see if you see any cracking or breaks at the connectors. Also, any device that is vacuum controlled can spring a leak and cause this symptom. A mechanic can check for a vacuum straight away, doesn’t take much time. If you want to try it yourself, you need a vacuum pump with guage.

Other possibilities include the IAC (Idle Control, as noted in the OP), and O2 sensors.

It might be a good idea to bring all engine maintenance up to the owner manual specs – that has to be done anyway – and consider to have a compression/leakdown test done at the same time. That would rule out (or if unlucky, confirm) major mechanical problems.

3

If the spark plug wires are 2 years old you should take a close look at them or replace them. Chrysler 2.0 and 2.4L engines are very hard on wires. Some models require spark plug and wire replacement together every 30,000 miles.

If it is not an ignition problem it is time for a compression test.

If the battery has recently been disconnected it would explain why the misfire monitor is disabled (no fault code).