Hey guys. I would really appreciate the help if you can give it.

A little bit about my car first.


My car is a 1990 Nissan 240sx with an SR20DET "Black Top" engine, cold air intake, T25 turbo, and a bunch of other stuff done to it.


My problem is.......everytime i am driving around town, I will push the clutch in and hit the brakes to come to a stop at a red light. Well, when I do this my tachometer drops from a normal 750 rpm to 1000 rpm to 500 rpm and sometimes down to 0 rpm where it stalls....obviously.


I got home, opened my hood up and checked the brake fluid......It is a rustic brown color but it is still full. I havent flushed the brake system yet until I get an answer that maybe it needs new brake fluid.


After checking the brake fluid and seeing that it is still full, I turned the car back on, let it idle at 900 rpm (normal) and then hit the brake. I noticed everytime I hit the brake the rpm gauge would go down to about 700-800 rpm. This makes me think maybe its the alternator when the brake lights come on or maybe I need a new brake cylinder......but then I got to thinking that when I brake with the car still in gear (not in neutral) the tachometer does not go down to 500-0 rpm. This only happens when I disengage my clutch or shift the car into neutral.


Any help would be appreciated.

vacuum leak inside your brake booster

brake booster is run off vacuum so when you step on the brake it leaks vacuum through the booster. most likely caused by a bad brake master cylinder so replace the MC and booster at the same time. good time to flush fluid also.

I took my car to Tires Plus today and they told me it was a bad brake booster. They had to special order the part and i'll get it fixed on monday. Thanks slideways. I got plenty of responses on other forums ranging from dirty idle air control valve, bad brake master cylinder, etc. etc.

any chance that could be the same thing with my car? completely diff car, but same problem!. mines auto, and a 96 240.its drops revs from like 7-8 to just barely 5 and sputters to stall. starts back up just fine...

I have since gotten this problem fixed. I replaced the brake booster and it kept stalling. So then I replaced the brake master cylinder and that fixed the problem.

So the brake master cylinder first. If its not that then its the brake booster.