Multiple Issues - Brake Booster, Valves?

[bradthebold]

A few months ago I started having vacuum issues while cold. It would run around 10" of vacuum and run poorly. Once it warms up, it normally runs fine around 19-20" vacuum. It is intermittent though, and doesn't happen all the time. When it's having the vacuum issue, you can hear air rushing under the dash. I thought it was the vacuum line to the boost gauge at first, cut at the firewall or something. I took the whole setup out and it seemed fine, I zipped tied things and it didn't make a difference. Later I figured out the sound comes from the brake pedal at the firewall. Pressing the brake when it's having the vacuum issue makes it better until you let up.

It's never had issues braking though, or boosting. I'm collecting parts to pressure test the engine, but I don't think it's going to help. I can't hear any leaking from the engine side and the vacuum line from the intake to the brake booster has good vacuum at the firewall connection at least. The line inside the firewall to the booster looks ok, so I'm guessing it's the booster. Anything I should check, or should I replace the booster?


The second issue I noticed when trying to hear for the vacuum leak. At low idle, it sounds like something is being tossed around on the passenger side of the engine. I haven't noticed it before today. At high idle it's gone or if you rev it up or drive it it's gone, but at least cold at low idle it's present. I'm guessing something valve related, but does it sound like an issue? Or if it goes away when it warms up is it fine? I'm using Rotella and it was right in the middle of the dipstick when I checked.

It's kind of harder to tell in the video. Most noticeable towards the beginning by the front of the air box.

Besides the rougher idle when it's leaking vacuum, it has no warm/running issues or codes though.

https://youtu.be/VDd_ymUSaxk

[bwizard]

Replace the brake booster

Sent from my S4's talk to text broke in my garage.

[bwizard]

Video does not work possible cam chain tensioner at idle less oil pressure also less when cold and it works off oil pressure

Sent from my S4's talk to text broke in my garage.

[bwizard]

Oh hey there is the video

Sent from my S4's talk to text broke in my garage.

[bradthebold]

I did have one cam chain tensioner related code come on once, but that was a couple years ago at least and it never came on again.

[rguil]

Did you check the one way check valve going to your brake booster?

That ticking noise sounds like the cam chain tensioner pads or perhaps lifters.
Id ignore it unless it gets a lot worse but thats just me.
A previous poster is correct when he said that your cam tensioners work off oil pressure but there is also a spring in there. You can run them unplugged just fine and not have vvt.

[bradthebold]

Ok, as long as the noise goes away when warm, I'll probably just watch it until the next timing belt then.

I have an 01 and I don't think I have that check valve mid-hose like 01.5 and 02's do, from what I found at least. Disconnecting the line at the firewall has good vacuum at that connection/valve.

[bwizard]

The leak is the seal where your brake pedal connects to the booster there is a rod and a seal I have seem it many times . Eventually it will get worse and affect drivability. Some leak only when depressed and some leak only when pressed

Sent from my S4's talk to text broke in my garage.

[bwizard]

Also is the rotolla t your running full synthetic? Conventional oils including blends contain ash that causes major sludge and will clog the tiny 100 mesh screen on the bottom of chain tensioners.


Sent from my S4's talk to text broke in my garage.

[Mille Bornes]

The check valve would be the bit that actually goes through the false firewall.

https://www.ecstuning.com/b-genuine-...ch/191611933f/

[bradthebold]

It's rotella t6 full synthetic. I've ran that the last 30k miles I've had the car and the last owner used synthetic for however long he had it.

That check valve seems ok. I have someone plug it with their finger while I looked inside and it held a solid 19-20" vacuum every time. Plugged in, even with it idling ok, pushing the pedal in and letting it out would drop it 3-4" each time I let out.

Is the booster repairable or the seal replaceable? Or do I need a whole new booster? Is the $150 TRW booster good, or do I need the $450 Audi one?

[bwizard]

Yes get a new one it's a safety issue for one but as far as I know they don't make repair lots for that reason. I would not get a made in China pos and I would not spend 450 from the stealership

Sent from my S4's talk to text broke in my garage.

[bwizard]

Repair kits* damn auto-correct

Sent from my S4's talk to text broke in my garage.

[bradthebold]

Ok, the booster was just delivered. Am I going to have to bench bleed the master cylinder if I take it off? Can I plug it after I take the brake lines off or will it already be empty? Or can I just take it off, put it back on the new booster, and pressure bleed without issue?

[bwizard]

Yes plug each line when you take off master ,bench bleeding won't be necessary but of course you will need to bleed at master and possibly wheels

Sent from my S4's talk to text broke in my garage.

[bradthebold]

Ok, I got it swapped this weekend and the issue is resolved. No more weird vacuum behavior or whooshing sound. It does idle a little low when first started, ~16in vacuum, but it's fine once warm. Bled the clutch and brakes several times to feel good.

A new issue popped up though. I test drove it and everything worked fine, then half way to work this morning, the ABS and ESP lights came on on the freeway. No flashing or red exclamation point or anything. I shut it off once I got to work and turned it back on and the lights are gone, but I'll have to scan it when I get home and see what's going on.

I replaced the rear wheel bearings as well. My brother was helping and pulled the axle on his side before pulling the wheel speed sensor, but it looked like it was fine when I pulled it out. They were kind of gross looking, but I didn't know if they needed coated with something so I left them. Hopefully pulling them and cleaning them is the issue. At least the bosch ones are only $65. And hopefully it's not related to the ABS module somehow.

[MetalMan]

A new issue popped up though. I test drove it and everything worked fine, then half way to work this morning, the ABS and ESP lights came on on the freeway. No flashing or red exclamation point or anything. I shut it off once I got to work and turned it back on and the lights are gone, but I'll have to scan it when I get home and see what's going on.

FWIW, it's unlikely you will find any stored codes in the ABS module regarding your temporary/intermittent ABS/ESP lights. That fault needs to be active to be able to pull relevant fault codes. Pretty annoying, but that's how it's been on my B5 A4 and B6 A4.

[audacity]

Ok, I got it swapped this weekend and the issue is resolved. No more weird vacuum behavior or whooshing sound. It does idle a little low when first started, ~16in vacuum, but it's fine once warm. Bled the clutch and brakes several times to feel good.

A new issue popped up though. I test drove it and everything worked fine, then half way to work this morning, the ABS and ESP lights came on on the freeway. No flashing or red exclamation point or anything. I shut it off once I got to work and turned it back on and the lights are gone, but I'll have to scan it when I get home and see what's going on.

I replaced the rear wheel bearings as well. My brother was helping and pulled the axle on his side before pulling the wheel speed sensor, but it looked like it was fine when I pulled it out. They were kind of gross looking, but I didn't know if they needed coated with something so I left them. Hopefully pulling them and cleaning them is the issue. At least the bosch ones are only $65. And hopefully it's not related to the ABS module somehow.

you don't need to pull the wheel sensors before the axle. if you do the wheel sensor was no positioned correctly they should never contact each other. meaning you don't need to remove to take out the axle.

[bradthebold]

I thought I had read that somewhere, that it could damage it. They looked completely fine though.

Does the sensor need coated with anything? The service manual just says not to install it before the axle is installed, which might have been what I was thinking, but I didn't do that. It does says to replace the clamping sleeve that it goes into in the spindle and to grease that whole thing up with brake cylinder paste. So should I just clean everything up and put it back in? Or if I can find brake cylinder paste, I'll use that.

[rguil]

I thought I had read that somewhere, that it could damage it. They looked completely fine though.

Does the sensor need coated with anything? The service manual just says not to install it before the axle is installed, which might have been what I was thinking, but I didn't do that. It does says to replace the clamping sleeve that it goes into in the spindle and to grease that whole thing up with brake cylinder paste. So should I just clean everything up and put it back in? Or if I can find brake cylinder paste, I'll use that.

The wheel speed sensors are variable reluctance sensors that generate their own magnetic feild like the crank position sensor. The good thing about them is they can be coated in greasy crap and still work but clean is more ideal. Especially on the tone ring of the axles and the sensor itself.

[bradthebold]

Ok, I'll clean them up.

Yet another issue is that the rear brake lights are staying on after the car is off. It did it in the garage when I was working on it and killed the battery. I thought it was because the hood was up maybe, but they were on after I got to work and I messed with it and they went off. When I went out at lunch, they were on again. I dropped it off for an alignment and they were on again. Pushing the pedal made them go off. I'll make sure the switch is being pressed and my booster rod is the right length, otherwise maybe the brake light switch could cause both issues? The ABS and ESP lights didn't come on in the couple mile trip to the alignment shop.

I'll have to see what codes there are, if any.

[bradthebold]

So I checked codes with the lights on and the engine and ABS modules has implausible brake switch signal codes. I pulled the cover off the lower dash and looked under there, and the brake pedal was only engaging 1/3 of the brake light switch, which must have been right on the edge of shutting the lights off. I adjusted the booster rod length to fully push the switch and compress the spring a little, similar to the clutch switch, and everything has been fine so far this week. No brake light issues and no codes, so that looks like it fixed it since it didn't have that issue before.