P0506 Idle Air Control System

[80sGuy]

Hey guys, Happy New Year. It's been a while....
Ran into a weird situation this evening. After a brief moment at the store, came out and got in my car, start the engine and put it in D to drive off, right away the car sputters a bit and shut down and stalled on the spot! I tried starting it and it just cranks and sputters. I added some oil and wait a few minutes. Then it started up fine afterward like nothing happened with no CEL whatsoever but then I had to check for codes with my handy OBD-II Reader and it came up with P0506. I've never encounter any problems with my car until now with this incident. I checked for threads but not much info with our year models and some never found any solutions. Has anyone experienced the problem before? If so what gives and where do I start? Clean the MAF, replace Idle Air Control Valve??? Online has a plethora of checklist. So far I made it home fine like nothing happened. Evening weather at the time (about 6PM) and around 58F.

The code:
P0506

[67Twisty]

That’s a generic p code for OBD2. If you have access to VCDS you can get a better diagnostic indicator. Our cars have electronic idle control at the throttle body and not a mechanical ICV. My bet is it’s a vacuum/PCV issue causing a misfire. Could also be a faulty coil pack or vacuum leak from the valve cover.

[80sGuy]

Thanks. I replaced the valve cover 'gasket' on 2016 at 62K (all genuine parts). I'm now clocked at 89K so no visible oil leaks anywhere like before, not sure if there should be any 'crack' on the cover itself, not that I can find when I took a thorough look over just tonight. Maybe I should replace those original coils? Just a few thing: it's been raining pretty heavy here in Socal and I've been hydroplaning quite a bit on the FWY on New Years eve. I also drove it again just a couple of days again in heavy rain. Not sure if that could be the culprit, but a thought indeed. I took the car out again tonight and it started up fine and drive normal with lots of boosts! I don't have Vagcom but my scanner has been pretty reliable over the years to solve simple common problems. This is new. Also, I'd like to also add that I do get the heating system (P2181) code from time to time because my thermostat is reading at the 1/4 or 11 o'clock range on the temp gauge.

[a4audi4fun]

Checking for suction level by removing the oil cap would be a test for the possible state of your PCV - it's not supposed to be really difficult to remove the oil cap. A bad thermostat or coolant sensor can affect the fuel mixture as the ECU gets confused about what temperature the motor has reached or is operating at.

Highly recommend as stated by @67Twisty that you get a proper VCDS scan - that will likely provide enough into to indicate a particular cylinder if in fact is coil pack related.

[67Twisty]

The two codes could be related. Sounds like your thermostat is sticking open, which is not uncommon at your miles especially if you have not yet replaced it as part of the timing belt job. The engine should be running between 200-210f and if it's not getting up to temp it can run rough and potentially misfire. Also not good for the oil system to run at lower than designed temps. If you plan to delay the timing belt job a bit further, I would replace the t stat asap. It's not a hard DIY, just a bit of a pain to get the hard pipe off and re-aligned with a new o ring. And the soft hoses will be baked on and require some persuasion to remove.

A bad coolant temp sensor can also cause the p2181 code, but that's less common than a failing thermostat.

I have found the life of the PCV diaphragm and related tubing to be a ~50k wear item on these cars. They are a more frequent source of vacuum leaks than the VCG and not a hard DIY to replace. I would add it to your list of maintenance items. The coil pack replacement isn't necessary unless your getting codes for specific cylinder misfires. But the cost of red top coils has come down a lot and it is a relatively affordable performance/maintenance mod. Other sources for vacuum leaks are the o ring for the dipstick and the vacuum pump at the rear of the head. You would notice oil leaking if the vacuum pump gasket was failing.

[80sGuy]

Thanks guys. I think I should first tackle the thermostat and PCV valve, and while I'm at it probably check and replace the cam follower also as a preventive maintenance. I drove the car all day yesterday as usual both on the streets and FWY and everything seem fine, just like normal. I've been wanting to fix the thermostat for the longest time. Been running it like this for over three years, of course I keep my eyes on it and the temp gauge do go back to the mid position - back and forth. Coolant level is on par. Will update.

[80sGuy]

Howdy folks! Just an update. Since the start of the thread, I replaced:

PCV and Gasket on 2/3,
Thermostat (and an o-ring for the smaller hard line hose attached to it) on 2/14,
Rear Coolant Flange, CTS o-ring, Upper Short Hose from flange, Cam Follower, Gasket for HPFP, rebuilt my Vacuum Pump with new gaskets on 3/31

Now I can confidently confirmed that the culprit to my initial stalling was due to the vacuum leak from the pump. I discovered oil drops on top of the lower flange hose (one to heater core). Also evident on the pump with dirt and grime. Probably been oozing oil for a while and progressing. Before the rebuild, I felt like the car would stall whenever I come to a stop - dropping rpm, hence the 'generic' code above from my OBD2 reader explains all. After the build along with all other new parts replaced the car now drives like new again. Lots of boosts and 'pressure' when letting off the accelerator. The hesitation is pretty much gone when accelerating from a stand still. Also the 'dropping rpm' is fixed so no more 'stalling' feeling, and above all no more oil leaks. This could also be another reason why I'm 'burning' or losing oil every now and then yet not significant, which I'm pretty sure that's the culprit.