B6 A4 1.8T Rough and Stumbling Idle

[Warren316]

Okay, I've had no luck at finding anyone with the specific symptoms that my car is having. Driving home on a long trip, pulled in and let the car idle for maybe 3-5mins while i was inside, came back out to a rough idle, but no CEL or anything. Touched the gas pedal and everything smoothed out. maybe 3 miles down the road CEL comes on and stays, but the car seems to be fine going down the road. Stop at the next stop light and get a terrible idle almost stalling, but again touch the gas and everything is fine. Drive home unload car and take to O'reillys to do an OBDII scan the say misfire on cyl. 1,2,&3, lean condition on cyl. 1 & 3, and random misfire. They recommend a tune-up but the car had new plugs and coil packs installed last March and only have maybe 10K miles on them. I decided to get the new plugs anyway just to see if would help, but it made no difference. I then removed and cleaned the MAF with CRC cleaner and leaft the battery unhooked for about 45 mins. Buttoned everything up, started the car ran fine for maybe 30 seconds and then right back to square one roguh idle nearly stalling, CEL light came back on and now a wierd oil/exhaust smell. shut it off and jumped on the net again, but i have been unable to find anything without just guessing and throwing parts at it. One new item i did find though is that it idles slightly smoother with the oil cap off? I can also feel a little suction when i go to remove it with the engine running. Can someone please help, i need to get it going again as it is our main family vehicle. Thanks

[Charles.waite]

Blown SJP I bet. Misfires on all cylinders sounds like a large air leak. A toasted SJP is the most common cause of this sort of thing cropping up randomly.

[old guy]

Blown SJP I bet. Misfires on all cylinders sounds like a large air leak. A toasted SJP is the most common cause of this sort of thing cropping up randomly.

Certainly a possibility. I agree that it's probably a vacuum issue. Are you noticing any changes in your brake pedal? What model year is your your B6?

[Warren316]

Certainly a possibility. I agree that it's probably a vacuum issue. Are you noticing any changes in your brake pedal? What model year is your your B6?

Nothing major or disturbing in the brake pedal, but i will check that when i get home. The car is a 2004

[old guy]

Nothing major or disturbing in the brake pedal, but i will check that when i get home. The car is a 2004

As CP noted the SJP is a pretty common component failure. But typically when it fails you will notice a difference in the braking ability since it provides vacuum to the brake booster. Your symptoms do sound like a vacuum leak somewhere. A quick way to help narrow it down is to systematically clamp off the various vacuum lines connected to the intake manifold and see if one of them makes a significant difference. I keep a set of Lisle clamps in the car for just such purpose but any clamp will suffice. If you find that a particular vacuum line makes a difference just follow the line until you find the offending component. Or you can post a pic or give a description of the line and we can figure out the defective component.

The reason i asked about the model year was to determine which PCV valve you have. From what I have noticed the '04 "Combination" PCV valve is prone to failure over the '02 and '03 PCV version.

[Warren316]

The SJP is on the driver side near the rear of the intake manifold correct?

I found one below, but would be better off wit the one from ECS?

http://www.oreillyauto.com/site/c/de...Stores=true#at

[old guy]

Yes that is your SJP. But before you replace it make sure that is the cause of your problem. The SJP should not separate into two components. If it does then you need to replace it. Here is what happens when the valve separates:



The "cap" should not separate from the body:

[Warren316]

Ok I got home and went out with a flash light, it wasn't separated until I touched it to make sure I was looking at the right part. As soon as I touched it I heard a little pop noise and then I could see the orange piece inside. So now it won't really run at all. I definitely have to get a new SJP, but do you think I'll need anything else? Possibly the PCV? I gotta get it running asap. Wife is not happy! Lol

[old guy]

Easy temporary fix with superglue. Just be sure to align the rib on the cap with the groove in the body of the valve.

[Warren316]

Ok, new SJP installed as well as the little 3 way vacuum check valve in your picture above. Now it is running again and no CEL, but the rough idle is still there and if I try to hold the rpms at say 1100-1200 it lopes from like 1000-2000 on the tach. What is the next best place to look? Still vacuum based issue?

[Warren316]

Another quick question, if I unplug the MAF and it makes absolutely no difference in the rough idle, could that mean the MAF is bad?

[old guy]

I wouldn't go after the MAF sensor just yet. You symptoms are still typical of a vacuum leak. Possibly another one of the plastic components around the SJP cracked during the install. Unfortunately that's pretty common. Also make sure you oriented the 3-way valve in the correct orientation. It will install either way. Just refer back to the pic in post #7. If you can't find any obvious vacuum leaks you can start by clamping lines off as described in post #5 and see if one makes a significant difference.

[Warren316]

Been working tons of overtime, so I haven't had chance to start diagnosis by clamping the lines. Its also been pretty cold here lately; I'd hate to crack a line by clamping it in the cold weather. Hopefully, I'll get home soon enough tomorrow that I'll have some light other than a flashlight and some better weather, I'll post up anything I find.

[Warren316]

Well, I finally got enough time and light to pick up some clamps and start tracing. Didn't take long to find the perpetrating line; its the one that runs from the throttle body, under the intake, and to the T-type fitting (connecting also to the oil filter housing and running to the back of the engine). Just as OldGuy said, putting the clamp on fixed the idle immediately, but it started to rain, and is cold so I came back in. I've been reading different threads and finding differing opinions: do I buy the whole replacement hose, buy some generic hose and fix the offending parts only, or delete the majority of the vacuum system as others have? Let me know your thoughts on this and thanks for your help everything you said was spot-on.

[old guy]

Well, I finally got enough time and light to pick up some clamps and start tracing. Didn't take long to find the perpetrating line; its the one that runs from the throttle body, under the intake, and to the T-type fitting (connecting also to the oil filter housing and running to the back of the engine). Just as OldGuy said, putting the clamp on fixed the idle immediately, but it started to rain, and is cold so I came back in. I've been reading different threads and finding differing opinions: do I buy the whole replacement hose, buy some generic hose and fix the offending parts only, or delete the majority of the vacuum system as others have? Let me know your thoughts on this and thanks for your help everything you said was spot-on.

The next step is to narrow it down a little more. Since you have an '04 you should have this PCV combo valve:


Is the hose intact from the intake manifold to the PCV valve? If it is you can disconnect the vacuum hose from the intake manifold and try blowing through the hose. If you can blow through the hose you need to replace the PCV valve. If you can't then you need to check all the connections on the other side of the PCV valve. In particular the "L" shaped hose connecting the "T" to the oil baffle above the oil filter. If that's OK check the hose from the other side of the "T" that runs up to the PRV valve on the back of the valve cover. Replace whatever you find defective.

I would not recommend deleting the block breathing system. It performs a very useful function and deleting it can lead to a lot of other unwanted issues.

Good luck!

[Cwee477]

The next step is to narrow it down a little more. Since you have an '04 you should have this PCV combo valve:


Is the hose intact from the intake manifold to the PCV valve? If it is you can disconnect the vacuum hose from the intake manifold and try blowing through the hose. If you can blow through the hose you need to replace the PCV valve. If you can't then you need to check all the connections on the other side of the PCV valve. In particular the "L" shaped hose connecting the "T" to the oil baffle above the oil filter. If that's OK check the hose from the other side of the "T" that runs up to the PRV valve on the back of the valve cover. Replace whatever you find defective.

I would not recommend deleting the block breathing system. It performs a very useful function and deleting it can lead to a lot of other unwanted issues.

Good luck!

Do u mean the vacuum hose that's in the front of the intake manifold?

Sent from my PH-1 using Audizine mobile app

[All_Euro]

The next step is to narrow it down a little more. Since you have an '04 you should have this PCV combo valve:



Is the hose intact from the intake manifold to the PCV valve? If it is you can disconnect the vacuum hose from the intake manifold and try blowing through the hose. If you can blow through the hose you need to replace the PCV valve. If you can't then you need to check all the connections on the other side of the PCV valve. In particular the "L" shaped hose connecting the "T" to the oil baffle above the oil filter. If that's OK check the hose from the other side of the "T" that runs up to the PRV valve on the back of the valve cover. Replace whatever you find defective.

I would not recommend deleting the block breathing system. It performs a very useful function and deleting it can lead to a lot of other unwanted issues.

Good luck!

Thanks OG, just used this to diagnose the valve and fix my rough idle issue