2005 Audi A8 rough idle
 

I have a 2005 Audi A8 4.2 and it’s having idleing issues if it’s idling for more than 5 minutes the rpm drop down to around 400 and then rev up to 8/900 and it happens fairly quickly as to almost sound cammed and when pulling into parking spots or reversing when your at almost idle speed it likes to randomly blip the throttle which isn’t what you want when your pulling into tight spaces I was getting lean codes and I smoked it out and traced it to a broken crank case vent which I replaced and the problem seemed to go away for a week or so but then I started getting rich codes and the problem came back I smoked it out again even though intake leaks usually cause lean codes but it doesn’t seem to have an intake leak so now I’m lost if anyone has any ideas on what it could be I would really appreciate the help

You don't say how many miles, recent repairs etc. Do you have VCDS? Do you get any error codes? If you have replaced the PCV then I would look at several things; first, make sure PCV hose connections are tight and the PCV hoses are good - also, sometimes those non-OEM aftermarket PCV valves can be flaky; check old/original vacuum hoses at the front of the engine under the trim cover (I highly recommend replacing all of them with silicone hoses, I replaced all mine and my idle went from rough to rock solid), fuel additive like Jetronic; or the O2 sensors.

Buy an OEM PCV valve. Worth the extra price.

The car has 352,000 miles on it and no that’s not a typo the only recent repairs being in the last 50k was the timing belt the crank case vent spark plugs and coil packs and one air strut but the last one shouldn’t effect the motor the only engine codes I have are p0172 and p0175 I have a friend with a snap on scanner but It doesn’t show any other codes besides those and I have a brake light on because one of the parking brakes doesn’t work I can look into replacing the vacuumed lines with silicone ones but they weren’t leaking when I smoke tested it so I don’t know if that is the issue

What should I look for in the pcv valve as far as knowing if it’s broken?

Wow, congrats on reaching that many miles. Very impressive! Sounds like the PCV you put in might not be OEM, you can try cleaning it as described in other posts here. But if it’s fairly new, it probably doesn’t need cleaning. Me, I would save myself the time and follow Mr Bally’s advice, install an OEM part and be done with it. Assuming the engine performs decently other than at idle, with that many miles I would really be suspicious of the vacuum hoses. Take a close look at them....I didn’t see any signs of cracking or leaking on mine, but I decided to just replace them anyway, and once they were out, I could see lots of small hairline cracks. Silicone hoses are cheap, I did the whole engine for maybe $30 in parts.

I bought the pcv valve from my local Audi dealer so It is the oem part but I’ll try replacing all the hoses with silicone ones today and see how that effects things

So I replaced all the lines and it seems to have fixed the check engine light and the rich codes but it is still idleing rough I did however notice that the random throttle blip is a direct response to steering wheel movement it gives it a 1200 rpm rev when I turn the wheel quickly but after idleing for a while it starts to do it without touching the steering

Those generic OBD codes are bank 1 and 2 “too rich” codes. You should get a proper vcds scan done as generic ones are not accurate. But in the absence of no other info you need to be looking at that. Dirty/failing MAF, sticky/failing throttle body, etc.