90 crx hf 310k miles.

whenever i push my brake in the idle will drop, when i let up the idle will go back to normal. is this a vacuum leak? Is it possible for a vacuum leak to cause the ecu to signal a code 4(crank angle sensor)? Sometimes the engine will stall on the highway, at the light, backing up just about anytime when im at the light it'll kill the engine and i've got to restart. It doesnt happen all the time, i drove it home tonight just fine without any problems though the idle will still act funny when i push the brake in.

 

Don't know about the idle thing, but for your crank code, do whichever one is easier for you first:

1) Borrow a known-good distributor, swap yours for it and see if it solves the problem.
If it does, replace your distributor. An SI distributor is the same one as HF.
90-91 LS one will work if you bolt it up funky (not all bolt holes line up)

2) With an ohm-meter, or multimeter set to measure resistance, check continuity between the distributor wires and the corresponding color wires on the ECU plug.
I don't remember withch pair is which sensor, but there is just three pairs, so it's not hard to just check all three of them, plus of you do a bit of searching either here or on google, you'll find the colors of wires and position on the ECU side of the CKP sensor wires.
The 3 pairs of wires for the three distro sensors at the distro plug:
Orange and thin white
Orange/blue and white/blue
Blue/yellow and blue/green

If one of the wires does not have continuity, replace that wire, or find the break in it and repair it.