Done a few tests still trying to figure things out before I buy new parts. My car when warm and when I put pressure on my brakes at a light etc my idle will fluctuate about 750-1000 rpm from 750 rpm to 1750 rpm. I replaced the main booster vacuum line and check valve...both ran tests on them for suction work fine...seems the booster may be holding pressure...pull the line out you here air exscape...(holding pressure) I did before have the problem with my old engine...so it's definetly something that is on the car that was there before (brake booster, MC and MC seal) When I got my car running before did the same problem but that was my mistake of not putting in a MC seal in it. I put one it last go around...not quite sure what it is...

brake booster? MC? or MC seal?

I dont think brake boosters rairly go bad?

If I plug off the booster line from engine and brake booster idles fine and steady...

it's definetly a vacuum leak seems like I got it narrowed down to Booster, MC or MC seal?

 

I had the same problem in my 91 lude and in my 91 crx eventualy, it turned out to be the diaphram in the booster had deteriorated. I just decide to cut it open after I replaced it just to see, and wallah.

My opinion is the booster. Dry or cracked enough and it will allow for a vacuum type problem when everything else is ok.

 

ya...im going to test it out on another car...have my car running while other car brakes lol...run the brake booster line to the other car....