1SLwLS1

iTrader: (6)

I have the set up listed below in signature. Sometimes I will be cruising along, AC OFF, disengage clutch, shift to neutral, release clutch pedal, and let the engine idle fall. I will wait for the engine idle to stabilize(900-1100RPM) and then I will apply the brakes. Sometimes idle falls a little bit(200-300RPM) and jumps back to where it was, sometimes it begin to hunt again, and can fall as low as 300-500RPM and quickly rev back up(1000-1100RPM) and then get stable again. Or, the 3rd condition, nothing will happen to idle quality, it will stay where it is.

Now the check valve at the booster should prevent a backwards flow of pressure back into the intake manifold. If this was malfunctioning, could is cause conditions listed above?

Or, how does the ECM respond to engine control parameters when the brakes are applied? Could this be a tuning issue(I think this has a higher chance of being the issue, hence the post in this section)?

carlrx7

not sure how the ecm responds, but i know the brake booster uses engine vacuum. if you have a cam that produces little vacuum, then i could see this happening as normal

1SLwLS1

iTrader: (6)

How? There is a check valve which is what connects the vacuum hose to the booster itself. If that were to fail, the reverse of flow would actually be a higher pressure and I know that wouldn't make the idle dip, it would increase it.

Now the quality of power assist is worse, and thats expected as the differential pressure between the 'low vacuum" and atmospheric pressure is less. This should not ever effect engine idle, unless I am missing something.

JonCR96Z

iTrader: (33)

Braking affects adaptive idle routines among some other things. Sounds like your idle tuning needs more work.