Hi folks, new here (but not to forums in general) and i have searched using a few search terms to no avail, so apologies if there is a similar topic.

I have a 56 (my07) V70 2.4 D5 185bhp auto with 173k

When the car is sitting at idle, the revs are ok, but as soon as I apply the foot brake, the revs drop quite noticeably, and it is getting worse, albeit slowly.
As it stands, it is enough for me to put the car in neutral and use the hand brake instead.

Any advice, please

Regards
Bashy

 

only thing I can think of is that the vacuum is being impacted by the pedal action. There are check valves in the vacuum line to the brake booster that may be gummed up or there may be a broken hose or small leak in the booster. Do you ever notice a hard brake pedal (like right after a cold start) or hear a woosh when pressing the brake pedal?

 

Hi, thanks for the reply, no hard pedal and no woosh either, there is the normal pft, noise when pressing it but that's all.

I do have another issue but I do not think it's related, 1st cold start is lumpy, a bit like it's only firing on 4 or struggling with the 5th, if that makes sens, been like that for about 2 years or more though... 😁

 

cold starts like a rich mixture so if you have a vacuum leak or a leak from the brake booster you'd get leaned out. Seems the two could be related.

 

Oh, ok, thanks, I may have to pay the garage to sort that then as i do not have the means to test for vacuum lakes

 

Hi again, to add a little more and excuse on the terminology

I checked the sensor thats on or near the air filter and that has suction.
I also took off the oil cap with the engine running and it sounds like, pop, pop, pop.....
...I am sure i read about that sound somewhere?

I think thats about the extent of my fault finding.

 

so the oil cap is sealing the crankcase system (ie the air above the oil level) - the PCV system uses engine vacuum to pull the unburnt gasses that slip by the rings and use an oil separator to keep the oil out of the intake. There's supposed to be some vacuum from the engine that balances the "blow by" pressure so you may actually see the pressure vary up and down slightly. The quick test is to put a latex "surgeons" glove over the oil fill cap. with the engine at idle you should see the glove suck in slightly or even puff up and down. If the glove inflates, it means your PCV system is clogged and needs to be serviced (otherwise that pressure will blow out cam seals and possibly main seals $$$$). If the glove sucks in hard, it may mean you have too much vacuum, suggesting a failed oil separator. (which can lead to oil being sucked into the intake soiling the MAF and throttle body).

 

Thank you for the info, i will test it with a latex glove, the car seems a lot worse if i do not use it for a few days, noticed that yesterday, there is also a strange whine at around 1000rpm onwards.

I took it on a 90mile journey yesterday and strangely the instantaneous MPG went up after about 30 miles, normally on a flat road it will do around 45mpg, this was like in the 60s and 70's
I am well aware that how th instantaneous works, i use the cruise control about 90% of the time as i find thats the best mpg, also my average went up far quicker than it normally would, plus i tickled it a few times.
As a rule it will do about 35/36 on average, its now on 37.3mpg, another tell is that i started with 180 miles left in the tank, when i got back home it was down to 145 miles left, this just isn't right
for this car, not in the 4 years I've had it.

Anyhoo, i will do your test when i get a moment and see what happens, sort of dreading that now considering the outcomes...