Engine Misfire During Idle Only

[GoogleMyAudi]

Hey guys, I've been beating my head over this issue for a couple of days now. The car has 72k on it and the DTC that pop up are Random Misfires, Cylinder 2 misfire, Cylinder 4 misfire, and VAG code 18320 Brake Booster Pressure Sensor open circuit/ short to B+

So now, I've performed a vacuum leak test with a smoke machine too. Only leaks I could find are a minuscule leak off of a tiny check valve that is located by the ABS module. And there was a lot of smoke coming out of the vacuum pump that's there. I don't know if it's suppose to do that.

Can a faulty check valve cause a misfire?! How bout the brake booster pressure sensor? Can that cause the misfire? I don't see any info about the brake booster pressure sensor anywhere! I'll post a picture a little later.

Thanks in advance

[milan2k13]

Any vacuum leak can cause a rough idle.. Replace whatever you see is leaking, clear codes and see what comes back.

Cylinder misfires, check the coils plugs and wirings. Replace as necessary.

[CyberPMG]

Nothing should be smoking.

Swap coils 1 and 3 with 2 and 4. Clear codes and see if it happens again. If codes are on the same cylinders, then you probably have bad plugs. If the codes moved to cylinders 1 and 3, then replace the coils.

[GoogleMyAudi]

I've replaced coils, and plugs. I'm heading over to the stealership to get the check valve and brake booster pressure sensor. The smoke is coming from the vacuum pump when I do the smoke test. It shouldn't be leaking right?!

[milan2k13]

I've replaced coils, and plugs. I'm heading over to the stealership to get the check valve and brake booster pressure sensor. The smoke is coming from the vacuum pump when I do the smoke test. It shouldn't be leaking right?!

I would highly suggest NOT to buy a simple two way check valve from the dealership.. I think they charge like ~30 dollars?
Click

Or get the US Plastics ones for a dollar or two..

[GoogleMyAudi]

I see, thanks for the heads up. Do these check valves have part numbers? I was gonna look on ECS

[milan2k13]

I see, thanks for the heads up. Do these check valves have part numbers? I was gonna look on ECS

Yes 058905291K .. my car has 5 of them plus 1 crank case vent valve, looks similar to the two way check valve. Yous is most likely the same.

[GoogleMyAudi]

Thanks a lot!!! Any idea on the brake booster pressure sensor?! I called the dealer and the parts guy kept saying the car doesn't have one, I'm trying to find the part # on it without taking it out.

[old guy]

So now, I've performed a vacuum leak test with a smoke machine too. Only leaks I could find are a minuscule leak off of a tiny check valve that is located by the ABS module. And there was a lot of smoke coming out of the vacuum pump that's there. I don't know if it's suppose to do that.

That is probably what's causing your rough idle. You have a leaking check valve internal to the vacuum booster pump. If smoke is coming out of there it probably means air is getting in through there at idle.

[old guy]

Any idea on the brake booster pressure sensor?! I called the dealer and the parts guy kept saying the car doesn't have one, I'm trying to find the part # on it without taking it out.

036 906 051 C Clicky click

[GoogleMyAudi]

Lol thank you by far the best thread I've ever posted!!