I need some help, please.

Just bought this 240, running beautifully. Drove it ~200mi from seller to home without incident.

The day after getting it home, fired it up in the morning, and it starts idling rough and trying to stall at stoplights. The issue seemed to go away after warming up. There's no lack of power, and it runs smooth with throttle at all times.

The next day, the problem seems worse (it actually did stall once), and seems to persist trying to die at idle even when warm.

Here's the kicker: sometimes this issue disappears completely, seemingly at random.

I replaced the IAC and the main (ribbed) air intake hose, and I cleaned the MAF. Seemed to run fine after that - until the next morning, when the wife tried to go to work and complained that it started trying to die again at stops. She brought it home after only running for about 0.5mi and parked it. I drove it a short while after, and it ran perfectly. I've been mostly unable to replicate the problem when I drive it - I've only seen the rough idle once with my own eyes.

Additional info: Even when running fine for me, I noticed that it idles higher than I might expect when in park or neutral - unless I turn on the AC. If I turn on the AC in park or neutral, the idle drops to normal. Switch off the AC, and the idle increases again.

What gives?

Please bear in mind that I'm a novice at working on engines, and I'm very new to Volvos.

Thank you!!

 

How are the "tune up" items? Plugs, wires, rotor, cap, etc? That shouldn't be the cause but still, good to know...

The MAFS could still be the problem--cleaning it doesn't really work.

How high is the idle? May be the PO raised it to avoid stalling?

 

The idle isn't ridiculous - just enough to notice that it's too high, and that it drops to normal when the AC compressor kicks on.

I bought tune-up parts: Bosch super copper plugs, NGK wires, and Bosch cap and rotor. I'll be installing them tomorrow or next.

I've ordered another MAF. I was suspicious of that, too, but wasn't aware that the obscene amount of canned MAF cleaner I used might have no effect. The new sensor is a new Delphi, not a reman.

We'll see what happens! In the meantime, if anyone else has any input, it's certainly welcome.

 

Just to follow up on this, since so may folks don't:

I did a little more digging, and it turned out the water pump was bad. Replaced that, topped off the coolant, did a full tune-up (plugs, wires, cap, rotor), and the idle problem seems completely solved! Crossing my fingers that it doesn't recur...

My best guess is that the coolant temp sensor was sending faulty info to the ECU because it wasn't properly submerged in fluid; now that the cooling system is full, the sensor is doing its job again, and the issue vanished.

Of course, it could be the fresh ignition system, too. Either way, they're things that needed to be done, and now they are. For now, the little brick is purrin' like a tractor-throated kitten!

If I run into any more issues, I'll post about it here in case it helps someone else.