V70 2001 2.4 petrol rough idle when hot
 

OK, guys, I have a really tough problem (to me it is anyway) my 2001 v70 2.4 petrol with 100k miles on it has a rough idle when hot, it starts first time every time with no problems but after about 15-20 minutes driving when its nice and warm it starts idling rough, I only have to touch the throttle and increase the idle up a hundred or two rpm from 800 to below 1000 to stop the problem. The code is p300 multiple misfire, and over the last couple of months I've tried to fix the problem, I've changed the coil packs (used items), checked the plugs, cleaned the injectors, throttle body, and MAF sensor, also changed the PCV valve and separation tank (a one piece item which was completely blocked), and checked hoses for cracks. To test the coil packs and injectors I've disconnected each in turn (while the rough idling is happening) and each has a marked affect on the idle speed, I've now run out of ideas. Can any you brilliant guys out there suggest what to do next, apart from take it to the dealers as I like to do things myself. Oh and be gentle I'm a newbie on here.

No mention of a coolant temp sensor being tested so maybe try that next.
Takes 5 mins and is free if you have a multimeter.
If the ECU thinks it's colder than it actually is, it could over fuel.......possibly.

Good point, I did check it a few months ago when I had a failed thermostat, but I will check it again. It's reading 91 degrees on the diagnostics, I think now you mentioned it that maybe a little low.

Diagnostics? Even better. You don't even have to lift the bonnet.:)
You need to read it from stone cold, preferably after being left overnight and before you turn the engine on and compare the temp with the temp on the dash or use a thermometer. It should be within 2 or 3 degrees accuracy.
Then watch its progress on a 20 min drive by which time it should be reading full temp.
From what you say, it sounds like it might be performing ok anyway but check to be sure.

I'll do that in the morning.

Thanks

OK, this morning I tested the engine temperature sensor using the diagnostic tool on my laptop and a thermocouple read by a multimeter attached to the thermostat housing outlet using a cable tie, cold start temps were 6 degrees on the computer and 7 on the meter, started the car and left to idle, temps slowly increased and after 45 minutes at idle the temps were 104 on the laptop and 97 on the meter and the thermostat opened sending the temp on the engine down and the meter up, thus controlling the engine temperature. I believe the engine temperature sensor is ok.
Next I revved the engine a couple of times and the rough idle started.
Any ideas?

How is idle controlled on this engine?
Is it all within the throttle body or is there an idle control valve also?

There's only the throttle body control that I can see.

A quick question, should the throttle body close all the way with the engine off, mines open a small amount

OK I've had the throttle body tested at ecutesting.co.uk and there are no problems with it. What else could it be?

Problem solved
 

Problem solved, the PCV valve box and pipework was completely blocked, which also blocked the breather channels in the cam cover, added engine cleaner to the oil and ran it for 2000 miles, which helped reduce problem, it was still occasionally playing up, so added more engine cleaner for another 2000 miles, then changed oil and filters, still played up under heavy load when towing caravan, but now after another oil change and 20,000 more miles no more spluttering, seems to be a common fault, I've seen a lot of V70s for sale with same problem. Talked to local machanic, who said lack of regular oil changes and cheap oil are a major factor to sludge build up in the PCV valve. I could have taken cam cover off but that ment removing cams and the spittering didn't bother me that much, so the slow and steady engine cleaning fluid was the way to go for me. Hope this helps anyone with the same problem.