Brake Pedal fluctuates, vacuum issue? cant find answer

[six2midnight]

Alright guys, before i start YES, i did search to find the answer to my problem. but everyone had a little bit different issues and from the things ive learned and tried it did not resolve my issue.

ok i have a 91 318 with a NV m50 swap.

My issues is brakes and sometimes..idle. when the car is off the brakes are very firm, a couple pumps (and by pump i mean maybe have travel of pedal) and brakes are completely firm. when i fire up the car the brake pedal falls about half way (which i believe is pretty normal)

my problem only occurs under 20% power i would say. if im going like 35 and apply brakes they are firm, and once power falls they will fluctuate, maybe get jittering, mushy then firm. This is is why i think its a vacuum issue where the pedal will go from mushy to firm.

i looked for vacuum leaks could not see any holes in the hoses (I will try starter fluid trick later this week).

I have taken out the ICV, and gave it a good clean, after replacing it, it worked! for about a day, brakes even felt better. Can the ICV affect the brakes too?

also applying brakes at low speeds, <10mph the brakes will chatter (firm then mushy then firm)and car will stall out. this doesnt happen all the time, but if i take it out for an hour it could happen 2-3 times. kinda dangerous :/ sometimes starting for the first time i will get idle jump too, up and down.

anyone else have any guesses? car has the 91 318 brake booster installed.

[EVillalonRN]

My brake pressure gives out at idle too.. works great after driving, but when sitting at idle, the pressure drops nearly to the floor. Works again after pumping a few times.

[six2midnight]

yeah mine doesnt do that, its fine at idle, well doesnt go to floor, it just gets firm and mushy

[jlevie]

This could be a bad check valve or a leak from the check valve through the booster. A hand operated vacuum pump/gauges should tell in any of that is the cause.

[six2midnight]

ok i was looking into this. the hose from booster to intake manifold well there is the T fitting coming out of the booster then hose right into manifold. is that T fitting connected to the booster the check valve? or do i not even have a check valve?

i did a little google research and it seems BMWs maybe have another check valve? or other car manufacturers include the check valve with the brake booster.

but if its another valve in line with that hose going to manifold i dont even have one. something like this



PS i did not do the swap, it looks like a pretty clean swap but just working out the kinks. thanks

[Boostesi]

there is an o ring around the base of the master cylinder i found leaking on my car with the smoke machine, if you took your master cyl out of the booster and did not replace that oring its probably a vacuum leak at the base of the master where it goes into the booster. worth checking out. fixed mine in about 5 mins

[six2midnight]

ill def check that. but dont want to bleed brakes right away. lol. if its just the 8 dollar check valve

[jlevie]

An E30 has the check valve in the hose connections.

[six2midnight]

even late model? I have a 91. so check valve IS NOT connected INTO booster? because ecs tuning says diff?

http://www.ecstuning.com/BMW-E30-318...Valve/ES61684/

**says USED IN THE BRAKE BOOSTER ASSEMBLY**

if not ill buy valve from like an m50 setup and just splice it into that line and see if that fixes it.