Engine: T5: Brake pedel causes uneven idle ?????

[100K+]

Yesterday while at traffic lights for no reason I decided to press down harder than normal on the brake pedal ( I'd been reading about soft n hard pedal here and wanted to know abit more about mine) Initially it depressed about 2/3 way down, then on the 2nd stroke about 3/4 down but very very very slowly it went down to about 2/3.
As the pedal was going down, the revs dropped from there normal 700ish but very steady to about 500ish then after about 5 secs started hunting upto 1000 down to 500 , acouple of cycles then stall.
Still the same now,but no CEL. I'll pull the air mass sensor and force a CEL and then clear the codes, but are these two events connected????

I have had air mass sensor issues in the past, but thought they were resolved.

Cheers

Bob

[outnumbered]

have you a vac leak somewhere

[Brendan W]

Yeah sounds like a leak either in the vac hose or the servo diaphragm. Presume you have a petrol motor. Run the motor for a bit then switch off. Repeatedly press the pedal , it should get harder and rise up. Keep your foot on the pedal and start - it should sink. Disconnect the vac hose at the servo end and block it up. Check it carefully for splits , cracks etc. If the problem goes away with the hose blocked it could be a servo leak.

[100K+]

Originally Posted by Brendan W

Yeah sounds like a leak either in the vac hose or the servo diaphragm. Presume you have a petrol motor. Run the motor for a bit then switch off. Repeatedly press the pedal , it should get harder and rise up. Keep your foot on the pedal and start - it should sink. Disconnect the vac hose at the servo end and block it up. Check it carefully for splits , cracks etc. If the problem goes away with the hose blocked it could be a servo leak.

Yes 2002 T5 Did check the Vac hose and found no splits.

Pedal responds as you say when engine on or off. I personally think its a master cylinder seal issue. I replaced fluid about 12 months ago but gained little pedal hardness.

My original querry was more about the perceived link between pushing the brake pedal extra long and hard and the then immediate effect of surging revs and cutting out.

As stated I did readand then cleared the codes - ECM 262A longterm fuel trim bank1 lower limit.
ECM 130A Air leakage intake
and the car now idles as normal, I just won't stand mega hard on the brakes at idle
BTW The ECM 130A code I have had for over 12 months and cant seem to pin it down, but does not appear to cause an issue.


Cheers

Bob

[Brendan W]

Brake pedals feel all wrong to me on these machines. They sink to the floor under sustained light pressure at idle - exactly like some sort of leak. Have a look at these and see if they ring any bells.
http://www.volvoforums.org.uk/showth...e+pedal+travel
http://forums.motester.co.uk/forum4/441.html
http://sprinter-source.com/forum/showthread.php?t=3114

[100K+]

Yes Brendan 100% thats how my pedal reacts.

BUT

why should that cause an irratic idle????????? or was it just coincidence???

and I don't think so


Also I think its master cylinder seals. My 2004 V70R has a rock hard pedal even with engine running, after a tiny amount of initial brake pedal travel.


Cheers

Bob

[Drak3n]

i have the same problem with D5 . sometimes , when braking on neutral , engine starts dropping on revs below 700 and whole car starts shaking . im noticing it for few years now , without solution. and few months ago , i also had problem with power steering - fluid leak , but after refilling its seems to be ok .

[Brendan W]

Originally Posted by 100K+

I think its master cylinder seals. My 2004 V70R has a rock hard pedal even with engine running, after a tiny amount of initial brake pedal travel.Bob

For me the acid test for master cylinder seals is how hard is the pedal after the servo is exhausted.
Have you checked non return function? Will the pedal kick back up if you switch off with the brakes applied ?
Afaik this long pedal travel thing is a diesel phenomenon - vac pumps deliver a heftier punch than inlet manifold vac. A possible explanation might be that you have either a master cylinder seal problem or air in the system and the long pedal travel is taking the diaphragm to a point where it opens up a bit.