Engine 850: B5252S/2.4/10v: Help. Rough running

[DaveNP]

Now I know the best way to sort this is to read the codes and do the basics but I'm in the middle of some 12 hour night shifts and I've got a busy weekend coming up too, so on a longshot, can anyone give me any suggestions on the following.
Back at the start of the year the car would occasionally run rough with a misfire when I put my foot down after coasting or plodding in traffic, it didn't do it very often so I couldn't replicate it but seemed to be when it was cold and damp. The car passed the MOT emissions no problem. Just before we were about to go away before Easter it started doing it more, it reminded me of when I had a Ford Fiesta and if you didn't move the air intake over the exhaust manifold in winter the cold air would cause 'icing' in the carburetor. I checked around the air hoses and found the one from the air filter to the manifold, which is one of those plastic bellows type had some splits in the folds of the bellows, I got a new one and fitted it when we got back and the car ran OK. Yesterday going to work and coming home this morning it came back with a vengeance.
The car starts and idles OK, about 1100rpm initially then down to about 900rpm, no changing up and down, if I put a load on the engine like turning the steering still no problem. When I press the accelerator the engine starts to run rough and if I pull away at normal revs there's not a lot of power and running really rough, I have tio rev it to about 2500rpm before letting the clutch out. Once driving it's similar, changing gear if the revs are below 2500 it will struggle, as the engine gets warmer it needs even more revs for a gear change.
So any suggestions of quick fixes to get me through the weekend?

[Luxobarge]

Take off dizzy cap and clean it, change it if it's very worn, clean/change rotor too.

Also try running in the dark with the spark plug cover off, see if you can see any stray sparks. If you can, then you need to repair/replace whatever is leaking, e.g. spark plug leads etc.

Also might still be vacuum related, try spraying WD40 or similar on the intake and vac lines while it's ticking over, and see if the engine note changes - if it does then you've got a leak. This isn't definitive, but can be a good place to start.

If you're going to spray inflammable stuff around the engine bay when it's running, I'd strongly recommend doing the "sparks in the dark" test first though, as stray sparks and inflammable vapour at the same time could cause a lot of paperwork.....

[chelle_belle]

Originally Posted by DaveNP

Now I know the best way to sort this is to read the codes and do the basics but I'm in the middle of some 12 hour night shifts and I've got a busy weekend coming up too, so on a longshot, can anyone give me any suggestions on the following.
Back at the start of the year the car would occasionally run rough with a misfire when I put my foot down after coasting or plodding in traffic, it didn't do it very often so I couldn't replicate it but seemed to be when it was cold and damp. The car passed the MOT emissions no problem. Just before we were about to go away before Easter it started doing it more, it reminded me of when I had a Ford Fiesta and if you didn't move the air intake over the exhaust manifold in winter the cold air would cause 'icing' in the carburetor. I checked around the air hoses and found the one from the air filter to the manifold, which is one of those plastic bellows type had some splits in the folds of the bellows, I got a new one and fitted it when we got back and the car ran OK. Yesterday going to work and coming home this morning it came back with a vengeance.
The car starts and idles OK, about 1100rpm initially then down to about 900rpm, no changing up and down, if I put a load on the engine like turning the steering still no problem. When I press the accelerator the engine starts to run rough and if I pull away at normal revs there's not a lot of power and running really rough, I have tio rev it to about 2500rpm before letting the clutch out. Once driving it's similar, changing gear if the revs are below 2500 it will struggle, as the engine gets warmer it needs even more revs for a gear change.
So any suggestions of quick fixes to get me through the weekend?

Had similar on my old 850 2.5 20v n/a, turned out to be about an inch of water surronding the spark plugs.

Craig.

[DaveNP]

Thanks both for the suggestions.
So I've just taken the cover off the spark plugs and the throttle to take the car for a spin down a dark country road and look under the bonnet in a dark layby, no stray electrics that I could see, no streetlights but enough moonlight I could see what I was doing but dark enough I think I would see stray electrics. However, when I took the cover off of the throttle I noticed that the rubber connector part of the tube connecting the inlet manifold to the Manifold Air Pressure sensor was badly perished, when I wiggle the tube the engine speed changes which suggests to me that there's the leak, I wouldn't have seen it if I hadn't popped the throttle cover off. I'll try the local dealer in the morning to see if they can get one or I'll have to improvise.

[DaveNP]

So as an update.
I phoned the local Volvo dealers (Marshalls Milton Keynes) on Monday and explained what I wanted, the parts guy said he'd have to look it up and phone me back, which he did soon after. I'd expected it to be a ready made 'pipe' and thought £20 to £30, turns out it comes in its component parts - a straight coupling, a right angle coupling, and the plastic tube by the metre, cost for all three (with far more plastic tube than I needed) less than £14 and they could get it in by the afternoon and call me, they actually called at about midday
Fitting it was fairly straightforward and there was an immediate improvement but not perfect. I suspect that tube had been leaking and getting progressively worse for a while as having driven around for the rest of the week the performance is improving which makes me think the ECU had learnt to adjust the fuel levels to compensate and is now having to relearn all of the fuel trim data, it's now pretty good for most of the usual driving conditions.