I have a '98 Dodge Stratus 2.4L Automatic w/260+K miles. Runs excellent but has developed a roughness at idle speed (like on 3 cylinders). But I’ve changed plugs, wires, coil etc and everything checks out. If I increase the idle very slightly by just touching the loud pedal the rough idle disappears. The rough idle occurs if the trans is in any gear, park or neutral.
There are no codes.
Any suggestions?
Have you checked the compression? If the compression is down in one cylinder or low in all cylinders do a ‘leak down test’. What does the manifold vacuum read? Is it steady or varying. The OBDII will not diagnose a worn engine or an intake manifold leak. It should catch a misfire but might not catch a weak cylinder i.e. leaking valve or rings.
With the mileage on this engine you could have a host of worn parts – valve guides, cam lobes, valve heads, valve seats, rings, cylinders, gaskets, etc.,etc.