My 04 has factory Hydroboost brake assist. Applying the brakes just sitting in Park causes a drop in engine RPM or a stall. The greater the pressure on the pedal, the greater the RPM drop. This does not seem to be affected by tuning. Has anyone seen this before?

 

Sounds like a problem with the power steering pump...

 

My hydro-boost braking is also dropping the engine RPM...Ditto on the power-steering pump...it's ready to sh*t the bed.

 

Could be, but it is not making any noises. Out of all the threads I could find via Google for various makes and models with similar issues, it is never stated how the problem was resolved. i.e. Was it the pump, or the hydroboost unit?

 

Have you every flushed the power steering fluid???

 

No. Pump(original) has about 45,000 miles on it.

 

Try flushing the power steering fluid.

Just like brake fluid, It breaks down over time as well as collects dirt, moisture and can start to plug up the feed side of the system.

 

Haven't serviced anything yet. Just did a little testing...

I notice an RPM drop just spinning the steering wheel in P/N, more if I crank it all the way, but no stall as I can cause by pushing hard on the brake.

I set the P/N and In Gear Desired airflow tables and the Desired Idle Speeds for both to exactly the same values. If I step on the brake in Gear, there is a very slight RPM drop but it does not stall, whereas in P/N it will stall unless I apply the brake very gradually.