Finally Experiencing Rough Idle, No CEL, Vacuum 15 in/hg

[brandonpham]

So i decided to actually drive to work today since there was road closures towards where i park for the train. On the way there, after leaving a light and then coming to a stop at the next time the following symptoms started:

Idle is about normal at 850 or so, but fluctuates slightly.
Car pulses at 1 second intervals
Vacuum reading at about 15 in/hg
No CEL
When driving the car is fine, hits boost, etc.
If i give it gas while stopped symptoms go away, revs fine, no misfires.
Once i turned the car off and turned it back on, it idled a little rougher and hung at like 1100 till it gave it some gas then it eventually dropped down to normal and gave the same symptoms again as above.
If i give it gas and let off the vacuum goes to 20-21, then settles back down to 15

Car is stock, changed plugs to NGK BKR7EIX about 10k miles ago. Has only a test pipe, r8 coils, BFI CC, stock tune.

Any suggestions? Tried to check under the hood but i had to run in to work so shes in the parking lot now, hopefully she won't leave me stranded lol.

Read through other threads but symptoms can be different for others. Just posting a thread since i don't get out of work till 7, by the time i get it back to the shop i won't be able to buy any parts really.

Thanks!

I'm thinking maybe N80?

[miA4]

So i decided to actually drive to work today since there was road closures towards where i park for the train. On the way there, after leaving a light and then coming to a stop at the next time the following symptoms started:

Idle is about normal at 850 or so, but fluctuates slightly.
Car pulses at 1 second intervals
Vacuum reading at about 15 in/hg
No CEL
When driving the car is fine, hits boost, etc.
If i give it gas while stopped symptoms go away, revs fine, no misfires.
Once i turned the car off and turned it back on, it idled a little rougher and hung at like 1100 till it gave it some gas then it eventually dropped down to normal and gave the same symptoms again as above.
If i give it gas and let off the vacuum goes to 20-21, then settles back down to 15

Car is stock, changed plugs to NGK BKR7EIX about 10k miles ago. Has only a test pipe, r8 coils, BFI CC, stock tune.

Any suggestions? Tried to check under the hood but i had to run in to work so shes in the parking lot now, hopefully she won't leave me stranded lol.

Read through other threads but symptoms can be different for others. Just posting a thread since i don't get out of work till 7, by the time i get it back to the shop i won't be able to buy any parts really.

Thanks!

I'm thinking maybe N80?

is it giving you almost like a slight misfire at idle? sometimes the rpm's will climb then drop back down to normal if you give it gas?

[brandonpham]

As soon as i step on the gas, shes fine, as soon as i let off, she drops back down and idles normal for a second, then starts pulsing as the vacuum drops to 15 in/hg

[miA4]

As soon as i step on the gas, shes fine, as soon as i let off, she drops back down and idles normal for a second, then starts pulsing as the vacuum drops to 15 in/hg

I believe you and I are having the same issue. I haven't checked the vacuum at all though. I just get an occasional rpm climb to about 1100 to 1500 until I press the clutch or gas and it goes away. I had my mechanic check it and we found no issues in VAG.

[miA4]

and by pulsing every second, do you mean that it feels like a slight misfire?

[brandonpham]

and by pulsing every second, do you mean that it feels like a slight misfire?

Are you running a boost gauge? Mines not occasional it was constant for the 15 minutes it started until i got to work. Again when i turned off and started the car too. I don't get a climb to that though, the most my idle will move is maybe from 820-850.

It feels like a choke/misfire.

[miA4]

Are you running a boost gauge? Mines not occasional it was constant for the 15 minutes it started until i got to work. Again when i turned off and started the car too. I don't get a climb to that though, the most my idle will move is maybe from 820-850.

It feels like a choke/misfire.

no boost gauge. I was debating on changing the N80 after checking all of the lines for a boost leak and finding nothing. is your car 6 SPeed?

[miA4]

I am experiencing that slight choke/misfire that you're saying though.

[brandonpham]

Yeah 6MT quattro, 125k miles. Its like a hard pulse, but idle isn't dipping low enough for the car to die. It stays around normal. Driving shes all bueno though.

[miA4]

Same here. I think my issue is probably two separate issues. I'm going to be replacing that valve probably this week as I hate that little pulse/misfire. I also feel like my fuel efficiency has gotten lower since it started happening.

[brandonpham]

How hard is your car shaking? Mine is pulsing pretty hard. I can't wait to get out of work and get it in the shop if it even starts...

[quattro guy]

Have you guys tried checking the pcv valve. Symptoms for a bad one are rought idle, try and remove your oil cap while the car is on. If its harder than what it should be and if the car starts running rough once removed you need a new pcv. Also to what i have read and experienced. The bkr7iridiums are a heat range colder that what is recomended for a stock car. Usually if you would be chipped you would go down a heat range because if the amount of boost you are producing. I speak from experience when i say iridium plugs are not a good idea for our cars. Mine was misfiring left and right, i went to the bkr7e, car pulled a bit harder and no more misfires. There is. Thread here that talk about plugs and heat ranges. Its a pretty good read and educational too. Just my .02

[brandonpham]

Have you guys tried checking the pcv valve. Symptoms for a bad one are rought idle, try and remove your oil cap while the car is on. If its harder than what it should be and if the car starts running rough once removed you need a new pcv. Also to what i have read and experienced. The bkr7iridiums are a heat range colder that what is recomended for a stock car. Usually if you would be chipped you would go down a heat range because if the amount of boost you are producing. I speak from experience when i say iridium plugs are not a good idea for our cars. Mine was misfiring left and right, i went to the bkr7e, car pulled a bit harder and no more misfires. There is. Thread here that talk about plugs and heat ranges. Its a pretty good read and educational too. Just my .02

Yep bkr7 are a step colder. I was running them ready for a tune, but that went on hold due to oil consumption. I was gonna go grab bkr6e after work.

Also i have the BFI catch can as said above, so no PCV.

[miA4]

How hard is your car shaking? Mine is pulsing pretty hard. I can't wait to get out of work and get it in the shop if it even starts...

you can definitely feel it in the car. feels like a misfire. sometimes it's bad, sometimes it's hardly noticeable.

[quattro guy]

Yep bkr7 are a step colder. I was running them ready for a tune, but that went on hold due to oil consumption. I was gonna go grab bkr6e after work.

Also i have the BFI catch can as said above, so no PCV.

I must have missed that about u having a catxh can, sorry. Well in my b6 at idle im at 21. Ill be more inclined to a vaccum problem then.

[DoThisMyWay]

A faulty PCV or crank position sensor will result in erratic idle, low vacuum and misfire like symptoms. If you don't have a CEL, you might want to check if the ECU is storing some codes. Just throwing that out there...

[miA4]

@brandonpham have you had issues where your car didn't want to start or takes a little longer than usual to start?

[Charles.waite]

Thats definitely a low vac reading. I was going to suggest PCV as well, but since you have a catch can, have you emptied it? Could be frozen and blocked due to the winter weather...

[brandonpham]

A faulty PCV or crank position sensor will result in erratic idle, low vacuum and misfire like symptoms. If you don't have a CEL, you might want to check if the ECU is storing some codes. Just throwing that out there...

gonna pull the scanner when i get back to the shop.

@miA4 the only time that ever happened was in the summer where it cranked a second longer than usual, otherwise it cranks and starts right up even in the cold.

@Charles.waite i checked my CC the other day, it fills up VERY slow. I've had it for like 5k miles or more and its barely 1/10th full. Also, today was 50 degrees out and raining, so i highly doubt its gonna freeze but i was gonna check that too.

[Phaxmohdem]

Those exact symptoms happened to me once when my oil cap had worked it self loose somehow. Check the cap and dipstick (and their seals) maybe?

I had similar but less pronounced symptoms when my valve cover gasket was leaky. When I pulled my coil packs out to change the spark plugs (because I thought they were causing a misfire or something) I discovered that the plug well on my #4 cylinder was full of oil due to a leaky valve cover gasket.

Edit: And leaky valve cover gaskets are themselves a symptom of the PCV typically... had to replace all that bidness to get back to a smooth idle.

[brandonpham]

So.... leaving work cold start got a check, once idle dropped as it does vacuum dropped and symptoms again. Drove for about 10 min, symptoms went away and drove fine still is. Got to the shop and scanned a p0011..... erased it hasn't come back still driving fine. Timing belt done at 80k car has 125k. Cam follower done at 115k or so.

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[brandonpham]

Any opinions ? Thinking it may be time to do cam chain and tensioner.

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[miA4]

i find it odd that yours gives a code. mine doesn't...

[BenMTL]

A faulty PCV or crank position sensor will result in erratic idle, low vacuum and misfire like symptoms. If you don't have a CEL, you might want to check if the ECU is storing some codes. Just throwing that out there...

I have to agree..... https://www.ecstuning.com/Audi-B7_A4...News/ES251228/

Not cheap part but directly related to all your symptoms;

Used by the ECU to control ignition and fuel injection, this sensor can burn or wear out over time. If the engine is revved with a worn sensor, misfires, motor vibrations and backfires can occur. There is a chance that your vehicle might not start altogether, so be sure to replace this faulty sensor.

[Charles.waite]

I don't agree with the crank sensor. Usually when that's going, you get really hard starts but once it's running it's just fine. My best guess is still some sort of vacuum leak. Make sure your boost gauge piping isn't leaking.

[brandonpham]

I don't agree with the crank sensor. Usually when that's going, you get really hard starts but once it's running it's just fine. My best guess is still some sort of vacuum leak. Make sure your boost gauge piping isn't leaking.

Boost gauge piping is 100%, checked it. I don't agree with crank sensor either, you get hard starts or a rough time revving up. If i give load/gas even the slightest bit the car was fine. Its so weird, these symptoms have not come back nor the check engine (only disappeared once i erased it). The P0011 is scaring me a bit. I haven't seen other people with similar symptoms and this check. It was almost like the car was off timing, but 45k later after the timing belt job thats odd.

Actually just checked carfax, timing belt was done at 92,112 miles, Conshohocken Audi dealership. So it actually has 33k on it. I feel like the 15 in\hg can be related to the car running off timing though. Still odd, and sort of mad it went away by the time i got back so i couldn't really look at it. Thinking i might do my cam follower for quick measure. I don't feel like a clogged oil pickup tube would result in these symptoms either.

[grassrootz]

This is interesting. I'm having similar issues. I recently had oil change and replaced Cam Follower. Cam and follower were fine (only black started to go away after prolly 35k checking it). My car is tuned but still has PCV, PCV seems to be going bad but car cleans itself out after a hard pull which I got some nice black plumes of carbon blow out. And back in business.

I'm just completely unsure where to start. I give a bit of gas and she's fine. Usually when coming to a light do I get the fluctuations. Is it a possibility that the breather tube is the bad piece not the entire PCV? I only took off the PCV hose to replace the Cam Follower could this have created a bad seal or corrupted the system? This is not the first time I've removed it but first time I am getting these fluctuations.

I am also wondering whats going on since there is more oil under the engine cover and I never used to see any oil there. Could it be blowing out the hose??

[onedumslack]

I'm not saying this is fully your issue cause it sounds like your symptoms are much worse. But I used to get a fluctuating idle when coming to a stop mostly when the engine was cold. I did a carbon cleaning on the valves and its gone now.

[miA4]

I'm not saying this is fully your issue cause it sounds like your symptoms are much worse. But I used to get a fluctuating idle when coming to a stop mostly when the engine was cold. I did a carbon cleaning on the valves and its gone now.

did it ever give you a DTC?

[onedumslack]

I was also throwing a knock sensor code for the one in front. I replaced both knock sensors at the same time as well. I didn't feel it was the knock sensor causing this though cause I was experiencing this for many miles before throwing the knock sensor code. But its very possible I guess the sensor caused it. It was doing this for a good 20,000 miles before throwing the code.

[miA4]

I was also throwing a knock sensor code for the one in front. I replaced both knock sensors at the same time as well. I didn't feel it was the knock sensor causing this though cause I was experiencing this for many miles before throwing the knock sensor code. But its very possible I guess the sensor caused it. It was doing this for a good 20,000 miles before throwing the code.

considering I found the part for about $30 new, I may change both sensors and the N80 for the heck of it.

[onedumslack]

Yeah, I picked up both sensors from europaparts for cheap so I just replaced them both and did the carbon cleaning cause I had to remove the intake to get to the sensors.

[crazyquik22023]

I don't agree with the crank sensor. Usually when that's going, you get really hard starts but once it's running it's just fine. My best guess is still some sort of vacuum leak. Make sure your boost gauge piping isn't leaking.

I agree with Charles. Definitely doesn't sounds like a crank sensor issue.

Boost gauge piping is 100%, checked it. I don't agree with crank sensor either, you get hard starts or a rough time revving up. If i give load/gas even the slightest bit the car was fine. Its so weird, these symptoms have not come back nor the check engine (only disappeared once i erased it). The P0011 is scaring me a bit. I haven't seen other people with similar symptoms and this check. It was almost like the car was off timing, but 45k later after the timing belt job thats odd.

Actually just checked carfax, timing belt was done at 92,112 miles, Conshohocken Audi dealership. So it actually has 33k on it. I feel like the 15 in\hg can be related to the car running off timing though. Still odd, and sort of mad it went away by the time i got back so i couldn't really look at it. Thinking i might do my cam follower for quick measure. I don't feel like a clogged oil pickup tube would result in these symptoms either.

Based on that fault I am betting your crank to cam timing is maybe off a tooth. Very easy to check so thats where I would start. If you verify timing is correct I would then start looking into cam to cam timing being off and possibly a damaged intake cam lobe from a broken cam follower. I know you said it was changed recently but if there was one time in the cars life where the follower broke and was driven with it broken u could have damage to the cam lobe and/or the HPFP.

[Charles.waite]

Just an idea, maybe your timing tensioner came loose and your timing is off...