Lean Codes After Intake Replacement

A6 All/ S6 All
#1

I figured I would start a new thread that is specific to the current issue that I am having.

I recently replace my intake manifold with a new one from JHM, along with installing the JHM intake spacers.

I had codes for the intake flaps being stuck open but fixed that issue by removing the last metal bracket on the front drivers side of the engine.

I now have new codes: P1081, P1085, P2189, P2187. These are all codes pointing to a lean mixture so I most likely have leaks or a leak somewhere.

I will be replacing my air distribution housing, as mine has a broken bolt fitting on one of the throttle body flanges and is distorted. But I don’t think that is the leak.

I will also be replacing my PCV/oil separator as these can cause this problem also. I have the same codes as referenced in this post: http://audirevolution.net/forum/index.php?topic=3967.0 The problem he had was a ripped diaphram in the PCV. I am hoping this is my problem but I am not sure.

I will also replace my PCV/valve cover pipe as on my car, one end is wrapped in electrical tape and and could be the issue. Its a good idea to replace it anyway.

Another thing I noticed yesterday is that I can hear a high pitched whistling sound coming from the air distribution housing coming from somewhere where it connects to the intake. I am thinking this is not normal? It sounds like it is coming from the passenger side but it is hard to pinpoint exactly where. Maybe what I am hearing is the PCV leaking? Anyone have this problem before?

Another thing I will also do is change out the valve cover gaskets. When I changed my sparkplugs, nearly every hole had a good bit of oil in them and I have read that leaking valve cover gaskets can cause lean codes. I also think it is a good idea as regular maintenance.

As for trying to diagnose the vacuum leak, I tried propane but could not hear any change in idle. But a change in idle would only happen if the leak in in the intake track? I assume if it is the PCV, this would not make a change in the idle as it is not in the intake path and so the propane would not make it to the cylinders? Am I correct in thinking that?

I think I will try starting fluid instead. Maybe I wasn’t using the propane correctly.

I will update this thread as I discover more or fix my problem. Thanks.

#2

One thing I also forgot to add is that when I take my oil cap off while the car is running, it is creating a sucking force trying to keep the cap on. From what I have read this is usually a failure of the PCV.

#3

I think I may have gotten my problem figured out. I got some starting fluid and used VagCom to monitor my fuel trims at idle by looking at measuring block 33. The fuel trims at idle were reading about +20% which is not normal.

I suspected that the seal between my air distribution housing/y-pipe and intake manifold may be leaking so I sprayed the starting fluid around there and sure enough the fuel trims dropped from +20 to about -5 then went back up. Each time I sprayed they dropped.

I took the y-pipe off and the orange factory gasket looked like it was not even compressed. So I put a very small bead of Reinzosil gasket material on the intake manifold flange, put the gasket on, and then put another bead of gasket maker on top of the factory gasket. I then let it set for about an hour and took a 40 minute drive to monitor fuel trims and see if I set a code. Previously, my car would set a code within 10 minutes of driving. On my 40 minute drive the fuel trims were consistently close to zero and there were no codes set. Yeah!

I am still going to change out the PCV and valve cover gaskets but for now it looks like my major vacuum leak is fixed. I guess there is a slight difference in the sealing surfaces of the new manifold and the old air distribution housing, probably less than a millimeter but that was enough to cause a massive leak.

I will monitor the car closely but I am 99% sure my leak is fixed.

#4

:’(

Well, that didn’t last long. Same codes are back again. Still waiting to receive my PCV/oil separator. Hopefully, that is my problem.

#5

Very difficult to find where my vacuum leak is. I am fairly certain that it is either where the air distribution housing connects to the lower intake or in that area. I tried spraying starter fluid in that area again while monitoring fuel trims and it looked like they went rich when I sprayed fluid near the front are of the flange.

My current theory is that my air distribution housing is a little warped and has a bend downward toward the front. The Reinzosil was not able to seal this leak. If that is the case, the housing would seal at the back of the manifold but not quite at the front. To check this, I put 3 of the orange gaskets between the manifold and the housing. Torqued down the gasket thickness is at least mm, maybe a little more. But there is almost no clearance between the surfaces where the housing bolts to the manifold in the front.

Going to run like this and see if this may fix my issue.

#6

So far so good. I have driven the car a good bit in the last day. Lots of starts and stops. Fuel trims so far look much more normal and I have not gotten any codes yet. So I think it probably was the air distribution housing.

I received in my new PCV/oil separator and the used air distribution housing that I purchased from eBay. Going to install those and see how things are. Crossing my fingers again.

#7

I had some similar issues - best way to find out where the air leaks are in that housing is get a can of engine start/jump start. While the engine is running spray suspected areas, if there is a leak the engines rpms will rise ( you will hear the rise) and that will fall when you stop spraying.

#8

That is what I have been doing and I think I have isolated it. I also changed out my warped Y-pipe housing. I cleared my STFT and LTFT’s and now need to drive and see it the codes come back or not.

If my codes come back, I will probably remove the JHM intake spacers and see if that is the issue.

I have considered that it could be fuel injector related but I doubt it since I was not throwing any codes before my carbon clean and intake manifold replacement.

#9

Another update.

Went for a long drive with several stops and starts, with regular highway, town, and interstate driving.

Codes P1081 and P1085 came back.

I used starting fluid and sprayed into the gap where the intake meets the engine block on the drivers side and monitored STFT. The STFT immediately went from about +5 to -15. I did this three times and it did the same thing each time. I also tried shooting the starting fluid on the other side and no difference.

I guess before when I thought it was the ADH, the starting fluid vapors must have been sucked into the intake near the runners.

So I will be removing the JHM intake spacers. It is probably a bad or nicked gasket that is leaking. But I think it will be better to just remove them. I think they are a good product but at this point I am sick of seeing my CEL come on and I just want to fix the problem. And I mostly drive the car casually and as a daily driver.

I will report back once I have more info. Shouldn’t take long to get the intake off and back on. I am an expert at this now. :wink:

#10

I had to get my first set of gaskets replaced, but it seemed to be partially due to installation error as well. New gaskets ordered/installed and the problem was solved.

#11

Well, I removed the spacers and re-installed the manifold. Cleared the codes and re-set the fuel trims, and then let is run and idle for a while. So far my LTFT are looking much better (much closer to zero on all four banks) than before, and my STFT are not fluctuating near as much as they were.

I am not going to say my problem is fixed but I think things are going in the right direction now.

When I took the spacers off, all of the areas where the orange gasket seal was supposed to seal looked like they were (I could tell as there was ring of oil everywhere the gasket was making contact) except on the second cylinder from the front of the car on the drivers side. That one had a spot on the spacer that looked like it was barely making contact. That is also the area that when I sprayed starting fluid, the STFT shot up.

And I followed the proper torque procedure just like in the Bentley manual. 3 steps doing 8 N-m, then 9-N-m, then 90 degree turn in the 1-12 numbered sequence starting in the middle going side to side until you finish with the bolts on the four corners.

The gaskets all looked good too.

May be I got an out of spec spacer? I don’t know. I just hope my vacuum leak is fixed so I can enjoy the car.

I will continue to monitor and report back.

#12

Seems like more torque would be needed for proper clamping once a second gasket is added. Then factor the spacer in… Wonder if an FEA analysis was done for the joint when designing? I wouldn’t think the torque spec would be as for the original joint.

#13

I tend to agree. But even with the spacers, on the last of the 3 steps in torquing the manifold, you turn the bolt 90 degrees. And every time, it feels like you are on the verge of stripping the threads. It made me pucker up every single time.

Maybe JHM needs to come up with their own specs for the final torque?

#14

Another update.

I have been through about 10 key cycles and well over 100 miles since removing the JHM spacers and I have not registered any trouble codes. Previously, it was only 2-3 key cycles and about 25 miles to register the P1081 and P1085 codes. I also think my gas mileage is a bit better and STFT’s are much more stable.

I will still keep monitoring but it is looking good.

#15

great, detailed post! Thanks for the update!

#16

Sounds like you had faulty gaskets or like they weren’t installed correctly the first time. I had the same issue with my first set and they sent me a second set. No issues since (knock on wood)

#17

I am quite sure I installed everything correctly. I followed the Bentley manual procedure to the letter and ended up having to do the install twice (once with old intake, once with new intake).

It could have been a faulty gasket but I could not see any defects anywhere in any of the gaskets.

I am thinking that JHM needs to come up with their own torquing procedure. The factory torquing sequence is designed for compressing only a single gasket. I think that with two gaskets, the final 90 degree turn is not quite sufficient to fully compress and seal both gaskets.

Maybe I am just the lucky guy that ending up having a problem when most people don’t.

#18

I agree. Sounds like you already had a list of small issues and you added the install of the intake spacers into the mix of a few issues.

Obviously almost all of the members have the spacers and with that issue free. from the updates and the tests you did there was obviously something off. with the top gasket then spacer and then the bottom gasket its can be a big tricky. Its not uncommon from some of the issues I have been emailed with from people looking for install help that the gaskets get installed wrong or just get slightly tweeked when trying to make it all come together.

The best way to make sure your issue free and what I suggest is the same thing I would suggest for the guys doing the oil pan reseal place in two studs long enough to pass through the gaskets and intake so you can remove them once you place in a few bolts. After that you need to keep in mind there is a proper tightening procedure going in a X pattern from the center out. Lastly the piece of advice I would give is to make sure you re tq the intake bolts after 2 or 3 motor heat cycles. This is where people end up seeing leaks if they ever get them.

I think if you get two new sets of intake gaksets knowing you have all of your other issues working out you should be fine for a second go at it. The intake spacers really help out this time of year.

#19

I think I will stay stock for now. Car is running good and I want to take a break from working on it.

I don’t track the car or intend to so it is not a big deal if I get heat soaked.

#20

Next time you get motivated to put 'em in, I highly recommend gold heat shielding the underside as well. With both of those on my car, the intake is barely warm compared to without the spacers and shielding.