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View Full Version : 1.8T Intermittent stumble/hiccup



TheRedGlacier
01-17-2017, 02:50 PM
Hey guys, I've been having an issue for a few months where randomly on acceleration, usually in the lower gears, where the car will like hiccup/choke/stumble for just a second or two, like the engine cuts out, but I've never really seen the Tach dip or anything like that. Just feels like a random misfire. New BKR6Es gapped to .28 were put in a couple months ago. The old plugs and the new ones both had this stumble. I took my friend's advice and removed one coilpack at a time, and removing any of them made the engine idle poorly as one would expect. None of them seem to be worse than the others.

I have a reasonable vacuum leak that I can't trace. It sounds like the leak is somewhere under the manifold.. but that's all a huge mess. I tried spraying brake cleaner on the lines, but nothing raised the RPMs. I replaced the 3 way check valve by the brake booster clutter, as well as the suction jet in that area. I know it may seem silly, but I'm unsure if the leak could cause it. The stumble seemed just as apparent before the leak became prominent.

This issue only seems to occur OUT of boost, usually while SLOWLY accelerating. Never got a MIL for it. I would use VCDS on her, but I don't know anybody who owns the shabang, and I don't have a working laptop.

I'm not really sure where to go from here. Doesn't really affect performance, it just makes driving slightly awkward.

2001 5 speed. 206,7xx miles.
Edit: GIAC X; Cold weather boosts to 12-14. In the fall, I was boosting to 16-18 psi. Vacuum is -16 idle in cold weather, -20 cold weather deccel. Vacuum -18 in warm weather. I also performed multiple boost leak tests, and I still can't pinpoint the leak. Still.. under intake. I'd assume its leaking from the same spot. Any ideas on how to find it?

Davdraco1
01-17-2017, 02:56 PM
Find that vacuum leak.

TheRedGlacier
01-17-2017, 03:26 PM
Any ideas on how to find it? I can't seem to pinpoint its exact location.

OverSpun
01-17-2017, 04:18 PM
check every one of your check valves. If you have not changed them recently... one or more are leaking and it can cause that (vac leak). You car has a lot of those. Behind the head, below the intake manifold, and one nearby your intake. The jet suction can also cause that. All are sorta inexpensive parts, replace them all if they are all very old since they get brittle and crack to leak.

The car should always run 20hg idle vac anytime as long your HVAC is off. My GIAC X used to boost to 20 - 21psi on my old 2001.5 A4.

BTW, your car would barely move with a bad coilpack and it would be on 3 cylinders but it sorta sounds like a subaru. Maybe go by autozone or to have the car scanned if you don't have VCDS or know someone with one. I suggest buying VCDS since its basically necessary while owning a B5.

I think you should have 4 of these if I am correct since you have a 2001. Previous have 3.
http://assets.suredone.com/1517/media-photos/cp020182-vacuum-non-return-valve-audi-a4-vw-passat-96-05.jpg

1 of these (behind the valve cover and in front the firewall)
https://ae01.alicdn.com/kf/HTB1KIRmKFXXXXcVXFXXq6xXFXXXX/OEM-Air-Pump-Vacuum-font-b-Check-b-font-font-b-Valve-b-font-Fit-For.jpg


jet suction-
http://thumbs2.ebaystatic.com/d/l225/m/mtRCII0V9Zj2c9Dp06oI0kg.jpg

TheRedGlacier
01-17-2017, 04:53 PM
Excellent Nick. Thanks yet again! I'll order some from Amazon. The last two pictures were the parts I've already replaced.

I've got a little CEL/ABS/SRS reader that works with the car, and I've got no CEL codes currently.

Davdraco1
01-17-2017, 05:18 PM
If you have access to a compressor you can build a boost leak tester and pressurize your system.

OverSpun
01-17-2017, 05:20 PM
Excellent Nick. Thanks yet again! I'll order some from Amazon. The last two pictures were the parts I've already replaced.

I've got a little CEL/ABS/SRS reader that works with the car, and I've got no CEL codes currently.

Sometimes codes arent thrown unless something is worse but your car definitely has a vac leak if its not showing a solid 20hg idle. It is a pain to replace the little check valves where they are. Especially the factory clamps. I used my dremel to cut them off carefully.

Second... double check your clamps on the 2 parts that you already replaced. Make sure your clamps are tight enough.

TheRedGlacier
01-17-2017, 05:25 PM
I gotcha. With the SAI pump running, I was just idling at -8 but once the RPMs dipped, its idling at -16 again. So I've ordered 4 new valves, and I'll try to replace those. That's the only thing that makes sense to me, as it seems to be an internal leak. Sometimes the idle is a little bumpy. Sometimes it is fairly smooth. Worse when its freezing out.

@Davd, I have built myself a little leak rig, and that's where we are now.. but it definitely helped me patch a couple small leaks in the past. Thanks!

OverSpun
01-17-2017, 05:33 PM
I gotcha. With the SAI pump running, I was just idling at -8 but once the RPMs dipped, its idling at -16 again. So I've ordered 4 new valves, and I'll try to replace those. That's the only thing that makes sense to me, as it seems to be an internal leak. Sometimes the idle is a little bumpy. Sometimes it is fairly smooth. Worse when its freezing out.

@Davd, I have built myself a little leak rig, and that's where we are now.. but it definitely helped me patch a couple small leaks in the past. Thanks!

Yea, that same thing happened with my current '01 A4 before I replaced my valves. The car just shuttered with a vac leak until I replaced the valves. The car has ~93k on it. Your valves should have been replaced by now, I would be surprised you still have the original ones.

TheRedGlacier
01-17-2017, 05:49 PM
That's a good sign then. They should be in by Thursday, so I'll be sure to update when I install them.

EDIT: All four of those one way check valves are definitely factory, or were replaced using one time clamps.

Davdraco1
01-18-2017, 11:18 AM
I had my primary 02 sensor misreading once it warmed up and the lambda readying was over -25%. The car was pulling fuel like crazy. Still never threw a code but I have vcds lite so I was watching the misfire counter rise when it was doing it. I've learned it won't always throw a code.

OverSpun
01-18-2017, 04:29 PM
That's a good sign then. They should be in by Thursday, so I'll be sure to update when I install them.

EDIT: All four of those one way check valves are definitely factory, or were replaced using one time clamps.

They could have been replaced before but the dealership uses those same clamps. I used legit clamps so I can easier replace again if needed.

You should probably check out your 2 factory clamps on your power steering cooler. My car was leaking a lot steering fluid and I'm glad I caught it before the steering pump didn't die.


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