Rev counter dips a bit every 10. second

Christiansen1968 · Post by **Christiansen1968** » 24 Jul 2020, 01:19

Hi,
I have a petrol 850 gle (144 hk aut.) with 200 k on the clock.
Its running fine with god power delivery and there are no error codes. But:
every 10. sec the rev counter dips a bit - in idle it dips from approx 800 rpm to 700 for a sec and the goes back to 800. At 2000 rpm it dips for a sec to approx 18-1900 rpm and then goes back. there are no dip in power! Its very consistant and it dosent matter if its cold or warm. Whats going on?

Kind regards Thomas

Cookeh · Post by **Cookeh** » 24 Jul 2020, 02:30

I've had similar experiences when there has been a vacuum leak. I would suggest checking the condition of all the vacuum lines, and replacing any that appear perished.

Christiansen1968 · Post by **Christiansen1968** » 24 Jul 2020, 02:44

Hi Cookeh

Any suggestions witch ones? Im not that familiar with my Volvo yet. I´ve only been the the proud owner for a month:-)

Post by **scot850** » 24 Jul 2020, 15:19

Pretty much any of the small lines in the engine bay. Some here suggest spraying something like WD-40 penetrating oil on the lines while running as it will help show the leak by how the engine is running.

As your 850 is a non-turbo there are a lot less lines, but at the age it is now unless the lines have been replaced before they will be turning to dust! Some of the cars still have a vacuum pipe layout under the hood. Worth checking if it is still there.

Good luck.

Neil.

Cookeh · Post by **Cookeh** » 25 Jul 2020, 06:24

Sorry for the delay in getting back to you. It really is difficult to point out a single probable culprit as any of them could cause the issue. Neil has covered it rather well.

Post by **jimmy57** » 25 Jul 2020, 10:14

Does the engine actually change speed or is it the tachometer changing only? DOes it do this when in gear moving the car or only out of gear? If aircon is turned off does this stop?

Christiansen1968 · Post by **Christiansen1968** » 25 Jul 2020, 11:41

Hi Cookeh

Thats quite allright!
Thanks for getting back to me.

Christiansen1968 · Post by **Christiansen1968** » 25 Jul 2020, 11:45

Hey Jimmy57

Its only the tacho.
IT does it regardless in N or in D.
Aircon dosnt change anyting. The dip is acually just like a little flitch...