Most of the time at idle, I'll be between -19 and -21 inHg. Every once in a while I'll feel the car start to idle a little rough, and notice I'm between like -13 and -18. Once driving it feels and boosts totally normally, and after a while (sometimes later in the drive, sometimes a few days) idle will be back to normal.
MIL comes on every once in a while, but then goes off after a couple days (Sorry, I can't remember what the code always is...the high idle one).
I've replaced a couple hoses in trying to find the problem. The "L" hose is good, I got a new suction jet pump, and a few other little pieces in that area. I also have the 034 breather hose kit, and I just did an oil change and new spark plugs.
I've noticed the problem start twice when I'm at work looking for a parking spot. I'll be in first gear giving it just a tiiiiny bit of gas, so I'm just barely moving, and it'll start being shitty.
Anyone ever dealt with anything like this? I think the parking lot driving might hint at something, but I don't know what. Any thoughts would be much appreciated!
Car is basically stock, I'm trying to deal with this before I take advantage of the REVO sale this month
It sounds to me like it could be your combi valve. The N112 valve only opens when the motor is in high idle. Check the selonoid and the line that run to the combi valve. That's my guess.
Little update: Got codes rescanned and came up with more than usual: P0507, P0300, and P0171. I rented a vacuum pump tool to try to test the combi valve, so I'm going to go give that a shot.
Originally Posted by http://forums.quattroworld.com/a6100/msgs/69.phtml
...Connect the vacuum line to your Mityvac hand vacuum pump and pull a suction on the EGR Valve. As you do this, the engine idle should drop noticeably. If it does, you have a good EGR valve and a good passage into the intake manifold. During this test, you are also watching the vacuum gauge on the mityvac. The EGR valve's diaphram should hold a vacuum. If it doesn't, the EGR valve will need to be replaced.
I did this with the vacuum line from the combi valve at the N112, and it did drastically change the idle, and did hold a vacuum.
Hm, this thread makes me wonder if I should be concerned with the fact that my car only shows about 12 PSI of vacuum at idle. (Just put the boost gauge in a week ago, so I have no other experience with it - it shows 23 PSI of vacuum on downshifts/overrun.)
Hm, this thread makes me wonder if I should be concerned with the fact that my car only shows about 12 PSI of vacuum at idle. (Just put the boost gauge in a week ago, so I have no other experience with it - it shows 23 PSI of vacuum on downshifts/overrun.)
You probably have a small vacuum leak somewhere. 12 In.Hg is a bit high. Should be closer to 20-21 In.Hg at idle.
Still have all my hoses and check valves and proud of it!
I did this with the vacuum line from the combi valve at the N112, and it did drastically change the idle, and did hold a vacuum.
What can I check next?
Need a little more detail. Did you disconnect the line between the N112 and combi valve or did you disconnect the line providing vacuum to the N112? If you were directly connected to the combi valve and it held vacuum your combi sounds like it is working properly.
Still have all my hoses and check valves and proud of it!
2003 A4 1.8TQ
APR stg2+, MTM injectors, Ecode FMIC, PSi testpipe, OC.T TIP, Hyperboost DV, B5S4 calipers, Goodridge SS lines, Stern firm snub, motor and transmission mounts, Podi, Vogtland Jr. Cup Kit, RS4 Rear Sway Bar, USP front and spacers front and rear
The end of the line that goes from the combi valve around the back of the engine to the underside of the intake manifold connects to the N112, right? I disconnected that line at the N112, pulled it up through IM, and attached it to my vacuum pump.
Thanks texasboy, but I replaced the sjp already :)
Understood. I assume the idle didn't change until you pulled vacuum on the combi valve. If that's correct then your problem is elsewhere. When you forced the combi valve open with a vacuum signal you changed the exhaust gas mix being monitored by the front wideband O2 sensor and the ECM reacted accordingly. Sounds like the combi valve is working as it should and there are no leaks getting through the N112.
Edit: Both of your codes are indicative of false (non-metered) air entering the intake stream. Among other things it can be a vacuum leak or a bad signal from the MAF sensor. What's intriguing is that it occurs intermittently and goes away. The next time you get the rough idle accompanied with reduced vacuum try unplugging the MAF sensor and see if the idle changes. If you have vag-com or VCDS you can check your MAF flow at idle to see if it is out of range.
Last edited by old guy; 12-17-2011 at 03:54 PM.
Still have all my hoses and check valves and proud of it!
Alright, tried unplugging my MAF while it was idling well, at -21.5 inHg, and then later when it was idling rough, and at -16.5 inHg; both times there was absolutely no change.
What does that indicate?
I just finished a waaay too long shift at work, so I'm gonna go collapse in bed. In the morning I plan on attacking every series of hoses I can with the vacuum pump to try to find any leaks.
That means it probably isn't related to the MAF sensor. Most likely a vacuum leak somewhere.The next time the idle gets rough try clamping off the vacuum lines leaving the intake manifold one at a time. If you find that one of them makes a difference continue clamping further down that particular line until you find the problem.
Another possibility is a dirty TB. But check for the vacuum leak first. Be sure to include clamping the line leaving the N80 purge valve and continuing to the intake manifold.
Still have all my hoses and check valves and proud of it!
You probably have a small vacuum leak somewhere. 12 In.Hg is a bit high. Should be closer to 20-21 In.Hg at idle.
Hm, that's disappointing. I wonder if it would have anything to do with T-fitting for the boost gauge - that's the only recent change to the system. I *think* I got it put together tightly enough, but there's definitely room on the T for more hose to go on - it's just that it's such a tight space to work in that it's really difficult to get it to go any farther.
I wonder if it would have anything to do with T-fitting for the boost gauge - that's the only recent change to the system. I *think* I got it put together tightly enough, but there's definitely room on the T for more hose to go on
If you are pulling 23 in.Hg when you let off the gas your boost gauge hoses are most likely OK. Sounds like you have a vacuum leak at idle.
Still have all my hoses and check valves and proud of it!
If you are pulling 23 in.Hg when you let off the gas your boost gauge hoses are most likely OK. Sounds like you have a vacuum leak at idle.
Thanks for the reply - from reading various other threads, it seems like you're the resident expert here, and I appreciate you taking the time to help me.
It pulls 23 and then after a few seconds, it drops down to 12. Apologies for the newbie/stupid question, but how is it possible to have a vac leak only at idle? Is there a valve that closes off a certain part of the system above idle, and if so, does that give an indication of where I should start looking for a cracked/broken/loose hose?
Just for the record, I don't *seem* to be leaking boost, as it maxes out at about 9 PSI, and gets there very quickly if I stomp on the gas (seems like less than 1 second from -12 to +9 PSI starting at 3000 RPM in 3rd gear, for example).
Well I can hardly claim to be the "resident expert". There are plenty of guys on here with extensive knowledge. I'm just an active enthusiast who happens to have a fair number of years maintaining and tweaking my cars. Now on to your idle issue:
A small vacuum leak may only manifest at idle. As soon as you come off of idle the amount of air from the vacuum leak proportionate to the total volume of air becomes increasingly insignificant. It sounds like you are interested in learning more about your B6 and doing your own repairs. Kudo's to you. Here's a thread that might help make a little more sense to the plethora of hoses and check valves on your motor. Clicky click. Once you have a basic understanding about what's going on with all that stuff the troubleshooting gets a a lot easier.
If I recall correctly (it was 8 years ago;-) a stock A4 B6 should produce around 10-11 psi and taper off to around 7 psi. 9 lbs of boost sounds just a little low. Here's a DIY for finding a boost leak (or potentially vacuum leak at idle). Clicky click. Another method I have found very useful in running down leaks is to methodically clamp off the vacuum lines leaving the intake manifold until you find one that changes the idle. Continue moving down the line until you locate the source of the problem. Sometimes it isn't that simple but by posting up what you did find will make internet car repair a lot easier for others to help out.
I have a set of these that I use all the time to isolate problems. You can pick them up at most autoparts stores. A simple but effective diagnostic tool.
Good luck!
Still have all my hoses and check valves and proud of it!
Well, claim it or not, you seem to provide timely answers to lots of people's questions, so, if it looks like a duck, quacks like a duck, etc, it must be an expert. :)
Thanks for the explanation and the links - that first one especially looks like good reading material for when I get home in the morning. (I work a 10 PM - 8:30 AM shift, and I'm headed out in about 10 minutes.) I'll have to stop by a store and get a set of those little clamps.
I just acquired a clamp to do some pinch-testing, but it's one of those days where my car just pretends like it's perfect, idling smoothly at -22.5ish.
We'll see if anything changes as I drive around, but until it starts acting up again...I don't know that there's much I can check.
Success! Or rather, progress. Pinching off the hose that goes from the intake manifold down to the check valve in the block breather system changes the idle and my boost gauge reads -22 :)
I've got to go to work now, but later I'm going to have someone sit in the car and watch my vac pressure as I pinch off the flow at different points.
I'm thinking maybe the block breather o-ringed billet thing isn't sitting/being held completely tight...We'll see, because I hate it when people make threads about a problem and never post what their solution was
Edit:
If you missed it in my first post, I have the 034 breather hose kit. My leak is in the "T" area of the kit, and I've come to two possible conclusions. 1. There's just a leak in "T," or 2. The 034 check valve isn't "strong" enough for this application. It's very easily opened from the back by vacuum pressure. I realized that possibly there is no leak, just the negative pressure of the IM at idle sucking the check valve open. Anyways, I just bought a vacuum line cap at O'Reilly's, capped off the port on the intake manifold, and zip-tied the 034 hose to the side, allowing it to vent to atmosphere. Whatever, I guess. Maybe sometime I'll try an OEM check valve and see if there's any difference. But for now, my CEL is gone and the car feels great.
Hm, 2 auto parts stores (O'Reilly and Autozone), and neither had those little hose-pincher clamps - both suggested just using a vise grips with a rag in it to protect the hose. Is that a viable method, or am I going to destroy stuff if I do it that way?
On a side note, I thought I had found the leak without testing, as the one-time clip on the breather hose from the valve cover was just flopping around, and the hose was loose at that connection, but replacing it with a "proper" hose clamp and making sure it was good and tight made zero difference that I could notice. Still showing about -12 PSI. I suppose that probably means that the leak is in that part or something in that system?
Last edited by olstyn; 12-23-2011 at 08:47 PM.
Reason: spelling error
Hm, 2 auto parts stores (O'Reilly and Autozone), and neither had those little hose-pincher clamps - both suggested just using a vise grips with a rag in it to protect the hose. Is that a viable method, or am I going to destroy stuff if I do it that way?
On a side note, I thought I had found the leak without testing, as the one-time clip on the breather hose from the valve cover was just flopping around, and the hose was loose at that connection, but replacing it with a "proper" hose clamp and making sure it was good and tight made zero difference that I could notice. Still showing about -12 PSI. I suppose that probably means that the leak is in that part or something in that system?
Another method for finding vac leaks, is by using an unlit propane torch. First, unscrew the torch burner tip from the burner tube, then attach a rubber hose on to the burner tube. Next, with the gas valve open, guide the tip of the rubber hose from the torch, along the various vac hoses, wherever there is a vac leak, the propane gets sucked into the hose, then burns in the engine, increasing the idle speed and smoothing out the idle.
Check your injector seals. My B6 had the same problem- went away when the weather was warmer or when the engine heated up. After cleqning my engine bay i saw some water sucked into the injector seat. Replaced these and the o-rings and she runs like new... Even with 151k
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Originally Posted by http://forums.quattroworld.com/a6100/msgs/69.phtml
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