2002 S40 - Rough Idle
 

I have a 2002 S40 that has been stuttering lately. It only stutters at low RPMs and it seems to only stutter with the AC is on. It was throwing codes about the mass airflow sensor and misfires on all cylinders. I replaced the sensor, put all new plugs in (OEM) and patched up a couple of vacuum leaks we found using a smoke machine. Everything was good for about a week and it started stuttering again. I found somewhere that this could possibly be symptoms of a bad EGR valve. But I don't even know if this car has an EGR valve.

Possibly related - when starting the car it take a few seconds of holding the key in the start position before it finally kicks over. The starter doesn't sound sluggish or weak, just takes a second before it revs up.

If plugs and a new MAF don't fix the misfires look to the coils and wires. The plastic will get hairline cracks which allow the spark to jump to the cylinder head instead of the spark plug. One person here said he fixed a hairline crack with epoxy.

There is no EGR on this motor.

Long cranking times before starting is a classic symptom of a bad fuel pressure regulator for this motor. Search fuel pressure regulator for more hits.

If the car starts right up/ but has low idle when putting it in gear/ and then evens out after a couple of miles /and then idles too high when put in park what could that be?
the idle at start up is 500.
the idle after a couple of miles is 800.
the idle when stopped and put in park 1000.
the idle when a/c is turned on 200.
also the other problem is the coolant fan continues to run and run for far too long even if I just turn the key to the on position without starting the car the fan comes on for 5 minutes. MAF? I replaced the coolant sensor with new. I cleaned out the idle control valve, not too dirty, nothing alarming in a car that has 168,000 miles on it.

Have you read the engine codes?

It actually isn't throwing any codes. Previously it was throwing MAS and misfire codes. But after new plugs and sensor those went away.

I'm going to order some parts today and I'll report back after swapping those out.