Fluctuating Rev Counter While Idling

Dr_Colossus

Hi, I bought my first car a couple of weeks ago, a 01 Volvo S40 1.8i SE with 110k miles on board. All sorted now with tax and insurance so only on the road a few days. Anyway obviously I'm not very experienced with motors and driving different cars so my question is as follows.

While idling and particularly on start up from cold, the rev counter fluctuates around the 1k mark, maybe between a max and min of between 800 and 1200 revs during a 1 or 2 second interval. While at the lower end it sounds like the engine will nearly cut out and at night with the lights on the lights dim and pick up again when at the upper 1,200 range which requires a small bit of acceleration to keep it constant. Is this common or what would the problem be? I'm half thinking the timing might be off or else the engine isn't always firing on 4 cyclinders? Would this make sense?

Further to this, I bought the car of a small dealer and given the age and mileage I was concerned about the timing belt and when it was last serviced. I got a one month warranty which covers the engine and gear box in the sale and the dealer assured me he would change the timing belt and service the car. He said he was in the business 25 years and his reputation was also at stake should it break and destroy the engine. Anyway the thing is I'm not sure if he did service the car as the oil on the dip stick is pretty black so now I'm wondering if he even bothered to change the timing belt and kit? Is there a means of determining whether the car was fully serviced and the time belt changed without taking half the engine apart to look at the belt?

Another factor that's spreading doubhts in my mind is that the car had an expired NCT so he was to put it through the NCT before the sale. This he did and he gave me the NCT report and everything looked in order. However where the overall doubt is stemming from is that prior to the NCT the front two tyres looked fairly worn on the outsides and insides. Like as if they were scrubbing with a tracking problem or perhaps driven over an extended period and poorly inflated. I commented on this when I first viewed the car and he said he'd change them if they were required as part of the NCT. When I went to collect the car after the NCT I noticed the tyres weren't changed and he said the NCT guys didn't even comment on the tyres, there is about 3mm of thread left in the centre of the tyre but I don't see how they'd have passed an NCT in their current condition. It is feasible he swapped on two other wheels just for the test to pass it but it doesn't infuse confidence especially with the doubts that I have as to whether the timing belt was changed and the car serviced. Obviously I'm most concerned about the timing belt as it's quite a big and expensive job to change and has dire consequences should it break. A newely serviced car with a new timing belt, water pump and kit was a big factor in me deciding to buy this particular car. So do any of you more experienced motorists have any suggestions as to the best course of action?

Apologies for the long post and thanks for reading.

voxpop

dont know about volvos, but they are the exact symptoms of a clogged idle control valve in bimmers


As for tbelt- you might want to get a receipt for the work. The rule i go by with tbelts is-when in doubt get it done. Usually when changed the mechanic will write the mileage on/around the belt.

metzengerstein

hmm sounds like the problem i had with my girlfrends car

and with some helpful posts on here i got it sorted .


i changed the sparkplugs they where in bad condition,i checked the oil there was a drop in it so topped that up, then i got some spray cleaner and sprayed it into the throtle body ,started it up and its running so nice now no rumbling or over reving

this was a seat ibiza so diffrent car but worth a look

Tr1PoD

Sounds like an issue with the ETM Electronic Throttle Manager. I had exactly the same problem with fluctuating idle a couple of months after purchasing a 01 S60. There was a recall for the issue in America but not here.

I rang Volvo and talked to a nice guy who was aware of the issue and that they would cover the cost of cleaning the Throttle Body and upgrading the ETM software which is meant to help.

This is just a temporary fix though and at some stage you may need to replace the ETM but a clean and software update has done the trick for me so far.

af_thefragile

Probably the idle control valve isn't working properly.

My car had this problem a while ago. First it used to fluctuate between 700-1000revs while idling. It was quite noisy and harsh.
Then after I got the timing belt done, it got even worse and everytime the revs dropped below 700rpm, the engine would just cut out. Made it very difficult to drive.

Then I got a new idle control valve on it and now it idles steady at 900rpm. No fluctuation at all.

Dr_Colossus

Thanks guys for the responses. Are the symptoms of a troublesome idle control value also a jumpy transition between 1st and 2nd gear? Any other symptoms relating to it?
Any idea what it cost you guys to replace/fix the problem?
Thanks again