sharpy46

can a bad brake booster cause hard starting or engine issues? sometimes when i start my truck while stepping on the brakes it starts hard....and the i gotta really mash on the pedal to get the beast ta stop lately/

CRamsey

iTrader: (1)

Yes, I believe a bad brake booster can cause engine starting and other issues. It's connected to the vacuum system, which also affects idle, etc. My 4Runner isn't braking well and the idle is all over the place. I plan on replacing the booster and checking for other vacuum leaks. Tracking down other leaks could be a real hassle, might as well replace all the tubes/hoses since they're 20+ years old... Do a search here for "brake booster" to see the symptoms of one going bad.

sharpy46

I figured...i just wanted ta throw it out there ta see what others thought. thanks 4 the input !

angrybob

EDIT for some clarity:

The only way you booster can affect engine perfiormance is if you have a leak in your booster through the control valve to atmospheric pressure in the cabin. This would have the exact same affect as having a leak in a vacuum hose before the check valve. If you have a torn diaphragm that is contained inside the booster, it will not affect your engine. Your two booster chambers will act as one large chamber and will eventually get to intake manifold vacuum, but your brake assist will be greatly reduced or eliminated because you will not have a difference in pressure between the two halves. However, your check valve will still block any return flow from the booster to the intake manifold.

sharpy46

the brakes have been crappy since i got the truck a cple months ago. no the pedal does not drop when i do that...im pretty shure the boooster is bad....but i was curious if it had anything to do with the starting issue i have sometimes. truck starts good when cold but it acts up sometimes when warm. ive done plugs n wires n fuel filter n timing and vaccum tests n stuff......usually when warm it wont start on the 1st attemp but when i shut the key off and try again it starts right up....low fuel pressure maybe...idk...i have anew fuel pump ta put in im just waiting 4 the gas ta get low so it will be easier to drop the tank.

angrybob

The above is a way over simplified booster explanation, but in general its true.



I clarified a couple things above...

A few quick checks should tell you for sure:

1. With the engine off pump the pedal until its completely hard. Start the engine and note two things: did the pedal soften at all? Second, after a say 10 seconds of idle does the pedal feel any better.

2. The second thing to check is if vacuum is getting to the booster. There is a plastic check valve on the vacuum line going from the manifold to the booster side. Carefully wiggle/twist the check valve to momentarily break the seal on the hose on the booster side. If you hear a hissing, you are getting vacuum to the booster. If not, check the engine side (probably not a booster problem). Go from there.

If #1 is NO and #2 is YES on the booster side, you have pretty much confirmed your booster is FUBAR.

As far as the hard starting problem, check the attachment. It's common enough that Toyota issued a TSB.

sharpy46

thanks for the info bob....does that attachment apply to they 3.0 engine as well? perhaps i have a bad temp switch or cold start component.

angrybob

No problem...

Unfortunately, its only a fix for the 22R-E & 22R-TE engines.