Revs rising & falling at idle - never happened before

[oliverpervasive]

Just a FYI - I have a S40 X reg auto petrol.

I had revs going up and down at idle - I could feel it through the steering wheel.

On investigation I found one of my vacuum hoses had come disconnected from the air filter (- goodness knows how as its well supported/connected) - shoved it back in and hey presto - back to normal running.

Im just saying its worth checking your vac hoses first before starting to dismantle things.

Mine was the one from the rear of the air filter.

[loelly]

To find vacuum leak spray (all) the hoses with brake cleaner,if it leaks you will hear the revs go up.

[CharlesStevenson]

Originally Posted by oliverpervasive

Just a FYI - I have a S40 X reg auto petrol.

I had revs going up and down at idle - I could feel it through the steering wheel.

On investigation I found one of my vacuum hoses had come disconnected from the air filter (- goodness knows how as its well supported/connected) - shoved it back in and hey presto - back to normal running.

Im just saying its worth checking your vac hoses first before starting to dismantle things.

Mine was the one from the rear of the air filter.

Thx for that. That reminds me of an 850 auto I bought off ebay a few years ago. It was cutting out when coming off the accelerator & when I got home I found that there was a massive split in one of the air hoses! How the previous owner hadn't noticed & dealt with it before I can't fathom! A few pieces of duck tape as a quick fix and all was good until I got a proper replacement.

[CharlesStevenson]

Just a quick update for anyone who searches for info on this issue in due course.

Over the weekend I removed and cleaned the IACV.

New gasket for unit was £3.30 from Volvo, couldn't find any on ebay.

Since cleaning and replacing it the up & down idle issue has *nearly* gone away, and seems to clear itself much quicker than previously, which suggests to me that I need to re-clean the unit, but more deeply this time.

A better (possible) solution than having to replace the MAF unit.

Will update over the weekend for future solution seekers.

[canis]

Originally Posted by emtor

I re-used the old gasket since it came off in one piece and I applied dish washer soap on both sides before re-mounting. The soap will harden into a hard but still flexible goo much better than any gasket paste I've tried. Here, (Norway) milk is sold in containers made from thin cardboard coated with wax. I use this material in combination with dish washer soap as gaskets where the pressure and temps are moderate. I've even re-used copper cylinder head gaskets (inboard marine engines) with dishwasher soap with great success.

Entirely agree. I've made gaskets out of cereal box cardboard, never heard of the soap thing though, I like that idea. There aren't many gaskets in these engines (brilliant design on the thermostat housing, for example), but in my previous engines I'd not even consider buying gaskets except for the cylinder head. If it comes as a kit, then I'll use the genuine ones if they're there. If not, cereal box. So far they've always worked perfectly.

EDIT: Thinking about this, I've been given the title of "honourary redneck" by my american freind, haha, due to my determined effort to never buy anything if I can avoid it, and fabricate stuff myself wherever possible. £3.30 isn't very much to spend - but that just goes to show how technically trivial it is. It's carboard!!

[CharlesStevenson]

Canis, "honourary redneck", LOL that's great!