revs and stalls when braking?!??!?!!

rt_blackpool · Post by **rt_blackpool** » Fri Dec 15, 2006 5:53 pm

its a bit odd, when i pump the brake pedal it revs its self from idle (900) to the highest i saw which was 1100.
with a bit of experimenting i found that it was when the pedal was released it would rev high and drop below 900, and once it stalled its self.

has anyone seen this before, or know whats causing it?
its just had new plugs, air filter, oil and oil filter, non of which is causing it im sure.

its a MK4 1.0L 1998

Musicfreek2002 · Post by **Musicfreek2002** » Sat Dec 16, 2006 10:28 am

I had this with my 1.0 1999 polo. It didnt affect the revs of the car when braking though, however i did have the same problem another time and just by cleaning out the throttle body the car ran fine again (ensure you open the flap inside and clean around the area where it touches the sides of the body)

gazza1286 · Post by **gazza1286** » Sat Dec 16, 2006 8:42 pm

The brake servo is connected to the inlet manifold. Pressing the brake pedal actuated this servo and may have an effect on the airflow into the intake. However the way it should work is that the engine creates a vacuum within the system which assists braking.

I would suggest that there could be a fault with this servo. If the vacuum is leaking via faulty seals or hoses additional air will be sucked into the intake manifold. This will affect idle speed as this extra air is by-passing the air flow meter and upsetting the air/fule mixture.

Have you noticed any problem with your brakes? Are they a liitle heavier than normal?

rt_blackpool · Post by **rt_blackpool** » Tue Dec 19, 2006 8:31 am

Musicfreek2002 wrote:I had this with my 1.0 1999 polo. It didnt affect the revs of the car when braking though, however i did have the same problem another time and just by cleaning out the throttle body the car ran fine again (ensure you open the flap inside and clean around the area where it touches the sides of the body)

how do you go about doing that on a MK4 polo?

rt_blackpool · Post by **rt_blackpool** » Tue Dec 19, 2006 8:34 am

gazza1286 wrote:The brake servo is connected to the inlet manifold. Pressing the brake pedal actuated this servo and may have an effect on the airflow into the intake. However the way it should work is that the engine creates a vacuum within the system which assists braking.

I would suggest that there could be a fault with this servo. If the vacuum is leaking via faulty seals or hoses additional air will be sucked into the intake manifold. This will affect idle speed as this extra air is by-passing the air flow meter and upsetting the air/fule mixture.

Have you noticed any problem with your brakes? Are they a liitle heavier than normal?

that sounds like what a mech friend of mine said, about the brake servo and the air.

as for the brakes, i couldnt realy say as i've only had the car a week and driven it once. but on the drive home, and when driving on my drive the brakes if anything a very light and i have to push fairly hard to get any kind of decent braking effort.

gazza1286 · Post by **gazza1286** » Tue Dec 19, 2006 9:59 pm

The brakes on Polos are quite good normally. It sounds like all of your problems will be sorted by changing the Brake servo hose. This comes with a check valve already fitted. they cost around Â£18 from a motor factor (probably a bit more from VW) Get someone who knows what they are doing to check this for you. It is just a case of removing the air cleaner unit to gain access then a direct swap for the hose running from the inlet manifold to the servo unit.

I had problems with this previously - spoke to a VW dealer who told me that the servo itself is virtually bullet proof so the repair wont break the bank.

carmadaaron · Post by **carmadaaron** » Tue Dec 19, 2006 11:20 pm

Mine was stalling everytime i braked!

My local garage cleaned out my throttle body and it went fine.
Try giving it a clean.

afcjay · Post by **afcjay** » Sat Dec 30, 2006 3:22 pm

id say brake servo to,had the same problem on a previous car myself too

Tris · Post by **Tris** » Sat Dec 30, 2006 7:57 pm

I would suggest giving the throttle housing a good clean out before you start spending money buying anything..

LeMeph · Post by **LeMeph** » Sat Dec 30, 2006 10:43 pm

plus even if cleanign the throttle body doesnt solve the problem it can d no harm really. Putting holes in your wallet can though! even if its only 18 quid, thats still a few pints down the pub!

Chris,