bzauche

Hey all,

So yesterday night I was driving home from work, and I came to a stop at a light, and all of a sudden the XJ is bogging down and sputtering like crazy. As soon as I let my foot off the brake pedal, it goes back to normal idle and runs great. Next stop light...same thing. The CEL then pops up, and luckily I was about to pass AutoZone, so I pulled in and had them check the code...P0705, which as far as I'm aware is for the neutral safety switch.

When I got home, I cleaned and re-greased the NSS, threw it back on, and checked the position to make sure everything was working great...started just fine in both park and neutral, and my reverse lights came on like they always do.

This morning, I head out to work, and I've still got sputtering/almost stalling under braking. It doesn't happen every time that I brake, but that's the only time it ever happens. The CEL is still on, but I haven't tried to clear any codes. I also don't know if it was throwing more than one code...the guy at AutoZone saw P0705 and unplugged the scanner without looking for more as far as I'm aware.

Any ideas?

pdowty68

My bet would be on a problem with the brake booster causing the vacuum press to decrease when the brake is applied. Check for vac leaks around your brake booster, with someone stepping on the brake for you.

bzauche

Even if I pump the pedal with the engine off, keep my foot on it, start it, and the pedal goes down? Am I just looking for a hissing sound or anything that sounds like an air leak? I'm pretty mechanically inclined but I don't know much about brakes.

pdowty68

go ahead and disconnect the vac line from the brake booster, plug it with something(don't let it accidentally get sucked in!) and then step on the brake pedal and see if it does it or not. If it doesn't do it, then you need a new brake booster, if It still does it, come back and tell me. But tell me either way.

XJ Sam

X2. Definitely a vacuum issue. Only way these things would be related. When you pull the vacuum line from the booster, disconnect both ends of the vacuum hose. Check both ends of the hose for splits or cracks. These are the most common places a vacuum line will split, especially on the side going to the manifold.

bzauche

Line connected: pump pedal, hold pressure, ignition, pedal goes down
Line disconnected: pump pedal, hold pressure, ignition, pedal goes down
Line plugged: pump pedal, hold pressure, ignition, pedal stays high

pdowty68

yeah, looks like you need yourself a new brake booster

bzauche

Just ordered one, thanks for the help! I won't need to bleed the brakes after install will I?

pdowty68

no, only if you introduce air into the system, at least I don't think you have to when changing a booster.

Parsnip

You will have to bench bleed the booster though

bzauche

How would I go about doing that?

pdowty68

yeah that's it! Since you don't expose the brake lines, you don't need to bleed then, but yeah I forgot about that.

Parsnip

Yep, but bleed the master, not the booster- assuming your replacing both, shoot it's a perfect opportunity to upgrade to the grand booster setup

bzauche

Not replacing the master cylinder, just had that done a month or two ago. Still curious as to how I bench bleed the booster before I put it in!

bzauche

Alright, so I'm on my way home from AutoZone with a new brake booster in the back seat...the ride is going fine until I pull in my driveway to check the mail. I roll the window down, get the mail, and then try to roll it back up. It doesn't budge, and the engine bogs down. I press the brakes to put it in drive, the engine bogs down. I open my door, the engine bogs down. It hardly lights up the interior lights. My battery gauge is reading right in the middle.

I'm clueless.