Hi all,
I have a 91 Prelude Si w 4WS. I just changed the brake master cylinder. I detached the vacuum hose to the booster in order to get the old one out- and when I did, I heard it lose vacuum. When I took the old mc out, there was quite a bit of corrosion (from leaking brake fluid?) dripping down the booster from the bottom of the mc where it attaches to the booster. I put the new one in, bled everything (inc bench bleed mc), and brakes work great now! However, the car is now revving at 3100 rpm. I thought the vacuum would re-establish itself when I hooked the hose back on, or at least after letting it run a bit. I put a little silicone on the new mc gasket, but not on the attachment plate. What am I missing, or what should I check for? Is it possible I tore a small hole in the vacuum hose while trying to remove it? Is the check valve malfunctioning?
Thanks so much for any input!!

 

Wouldn't it make sense that you did something to make it leak at that hose. The best thing to do is to use some sort of very fine mist of water and gently spray it in that area while the car is idling. When it changes the idle, you've found the problem. Make sure it is a very fine mist.

 

Hi all! Well, I tried spraying brake cleaner around the fittings and no change. I'm pretty sure it's not a vacuum leak after all. I fiddled around with the cables and hoses in the area- trying to see if I could get any reaction from the idle, and when i moved the throttle cable around, the idle went haywire. I think what happened is that when I took the old MC out, I had to move the throttle cable out of the way (w/o disconnecting it) and I think it slipped out of adjustment, like the adj and lock nuts were just slightly loose enough to let the cable slide out, but not back right away. So tonight, I was fiddling around those nuts, and got the idle back to where it should be. Took it for drive, and then when sitting at the auto parts store, the idle started that 'Honda' surge... and did it randomly on the way home. I think it's mostly fixed, but I'm still missing an adjustment somewhere, it's just not quite smooth.