Brake pedal sinking sometimes

[jp_ek4ferio]

Well lad need some help. My brake pedal will sink if the engine is idling however if I was driving along the brake pedal is fine. also if I pump the brakes with the engine off I get a stiff pedal as expected but if I hold down the pedal and start the car the pedal sinks to the floor ?? Need help asap as the car has nct next week

 

[oifovo]

have you bled the brakes recently? Sounds like there's air somewhere or faulty master cylinder? I'd start by bleeding the brakes and take it from there. Also do you run ABS?

 

[**MUGEN**]

This was happening to my ek9 recently, bled the brakes serveral times, no air in the system, problem still occurred. Needed new MC in the end.

 

[jp_ek4ferio]

Yes i changed the master cylinder. Bled the master cylinder and the brakes. Was thinking maybe brake servo or maybe there is still some air in there. ?and no I don't have abs

 

[jp_ek4ferio]

Also I forgot to say if I keep my foot on the brakes with the engine idling and the pedal going to the floor the engine will sometimes cut out

 

[irf]

Sure your replacement ms isn't faulty? Did you bench bleed ?

 

[jp_ek4ferio]

I drove the car it came out of last October and was fine but has sat up since so maybe it's gone faulty. Yes i did bench bleed it. Is there any exact way to tell between master cylinder and brake servo ?