I did some brake caliper cleaning the other day and when I went to make sure everything was in order I noticed that when I pumped the brakes my idle would drop from 750RPM to 400-500 RPM. What would cause this and how can it be fixed. At the time I had trans in neutral(manual). Also, want to replace engine coolant temp. sensor, how much PITA is it to remove intake manifold? The bolts on the manifold are pretty well aged, where they may not come off. Any advice appreciated.
Thanks for any help.
Rob Mac

I had similar symptoms while pumping the brake, my idle went up.
Its the brakebooster or the check valve.
Find out how that works, you have to understand that first,
and perform some checks like blocking the hose from intake to booster
while checking only, don't drive like that.
Read the FAQ.
I got a used booster from the junkyard for about 25 $,
and its fine since then.
I posted my experience here about 3 month ago.