Strange Idle problem

canadianmk3 · Post by **canadianmk3** » Wed Nov 28, 2012 11:13 pm

My Cortina Mk3 2000 will idle at about 800 rpm, choke off, fully warmed up, and it will be real lumpy. If I hit the brake, the idle will smooth out and the rpm will rise to about 1200 rpm. It does this when cold too with the choke off. I know the booster is functioning. Could it be a vacuum leak between the booster and the manifold? The hose is 40 years old...

enfoprefect · Post by **enfoprefect** » Fri Nov 30, 2012 12:20 pm

Definitely sounds like a vacuum leak but not the hose. That should leak all the time, not just with the brakes applied. I would really suspect the diaphram.

JAN · Post by **JAN** » Sat Dec 01, 2012 12:56 am

It sounds like an over-rich mixture; pressing the brake pedal draws air from the servo to weaken it. The problem might be in the carburettor.