Hi all.

I have a 1990 3.0 5-speed - I've noticed that when braking, the engine will sometimes dip in RPM (from about 1070-1100 RPM rough idle) to about 800 RPM and then it goes right back up again. I know the idle seems high, but I don't have the time or money to start messing ECMs for my truck that is otherwise running fine.

Anyway, it's just a temporary blip - as if fuel was being cut off for a split second. I don't think this is the case since the fuel filter was replaced about 2000 miles ago, and it only happens when I apply the brakes.

Weird.

Any ideas about where I should look and whether I should be worried?

Thanks.

- Paul in AZ

 

It might have something to do with your powerbrake booster. As you know vacuum is supplied to the booster from the engine to make braking easier and sometimes they may develop a pinhole leak and when the brakes are depressed will cause a slight leak which will cause the engine to raise or lower slightly. good luck

 

It might have something to do with your powerbrake booster. As you know vacuum is supplied to the booster from the engine to make braking easier and sometimes they may develop a pinhole leak and when the brakes are depressed will cause a slight leak which will cause the engine to raise or lower slightly. good luck