wthdidusay82

iTrader: (15)

I just realized after turning down the idle on the car seems to have made it run alittle smoother but when I come to a stop the cars rpms will drop and practically want to die out sometimes. It all depends on how hard i push that pedal though, the harder i push it the more the car bogs down.

My brakes seem like they are working fine to me but what could be causing my problem ? I would think the brakebooster but I am not sure because my brakes seem to work fine so Im not sure if it is that or what it could be. Maybe its something easy to fix ?

Anyone ever have this problem ? Any ideas ?

bmwrx7man

iTrader: (2)

my man wat up .maybe the dirphram in the brake booster or w/e u spell it

wthdidusay82

iTrader: (15)

Id have to somehow test it to know thats what it is for sure , i dont want to replace a good part but who knows.

Maybe it could be the brake master cylinder ? I donno

BrettLinton7

iTrader: (33)

This happens to me, but is barely noticeable.
If it's really bad, you might want to replace your BAC Valve or whatever

But like I said, my 7 barely does this and nothings wrong with it

wthdidusay82

iTrader: (15)

My bac valve is removed, could this be what is causing the problem ? I had raised my idle up before to bout 1200 and it went away but running around 750rpm idle it makes the problem much much more prevalent.

helghast7

iTrader: (6)

try this as a test now before you blow this off try it for real because this is happeneing to my car slowly....ok....start the car let it idle for a while.....now turn on as much electrical stuff as possible (like...everything) does it do it then? if so its your alternator going...or you need a higher output one (and to all the critics your alternator loosing power WILL lower your idle).
....anyway....if not it could possibly be those infamous vaccum leaks....but hey i dont no....just making you think...trying to help

Alex Rodriguez

iTrader: (137)

Inspect the hose that goes off to the UIM , if its bad that could be your problem also oh and does it still have the oem valve

wthdidusay82

iTrader: (15)

There are no valves or anything from the acv , egr, bac or pcv valve. The entire emissions rack was removed, along with that airpump and everything was capped/blocked off. The only thing left is the stock omp.

Alex Rodriguez

iTrader: (137)

no no no...on your stock brake master cylinder theres a 90 degree tubing that comes out , theres a hoses that connects to that 4" on the hose theres a OEM vacumm fitting then i goes back to hose then it routes it way on the firewall along with your brake lines and into your UIM.

I never said emissions related valves

helghast7

iTrader: (6)

did you try it? no? ahh well i tryed to help

clokker

iTrader: (2)

The only way the alternator could be involved in this scenario is if the draw from the brake lights is excessive.
Easily checked by disabling the brake light switch at the pedal- if the idle still drops then it ain't an electrical problem.

Much more likely to be a vacuum leak anyway.

RotaMan99

I know you disconnected the brake light switch but to just add to this, you have about 10amps worth of lights at the rear of the car when you hit the brakes. More then enough to add strain to the alt and lower the idle.

Get a vacuum tester and test the booster but you will probably find that its good and you will probably need to raise the idle to around 800-900 rpm. This is what the BACV is good for. Removing it serves no point. I removed mine 5 years ago and have had my idle around 850-900 without problems. Idle does drop when hitting the brakes but that is from the lights in the rear and some from the booster. Goes down to about 700-750rpm.

The engine has very little power (HP/Torque) at lower rpms such as 750rpm. So it takes very little for the engine to react negatively to something.

When you are pressing on the brakes or pumping the brakes, you will be affecting the vacuum in rear of the LIM which will cause the engine to lower or buck around if you are pumping the brakes hard.

If the booster was leaking, then without even pressing the brakes the engine would essentially have a vacuum leak

A quick easy way of testing the booster for leaks is to turn the engine off, depress the brake pedal many times and pedal should get very hard and should be hard the whole time you press on the pedal. The pedal should never slowly go to the floor.

That test serves no purpose. That will tell you nothing about the condition on the alternator. That tells you the alternator is possibly WORKING. The alternator does not loose power. It has the possibility of not creating enough power which will not lower the idle as much or possibly the same depending on what is bad in the alternator.

Read this thread. It tells you how to test your alternator among other items
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/battery-drain-issue-628141/

Not at all. The master cylinder has nothing to do with how the engine runs.