Lost. Rough Idling and stumbling=useless A4

[Boone]

Background- Previously had misfires over the summer which fired the CEL and codes. So I replaced all spark plugs and regapped them, and everything was good for a while. A couple weeks later, I started getting mild stumbling during hard acceleration, so next I replaced the Coils with the new F versions. This did nothing, and I still got mild stumbling during hard acceleration, but it did not fire any codes. So, finally I took it in to Audi to have the recall parts replaced (PCV, IMRC, and something else), which they did free of charge. Thinking it was the PCV gone bad (which was bad...it had some severe suction on the oil cap while running) causing the stumbling, I started the drive home. Once on the highway, I accelerated relatively hard, and found the same stumbling was still there. I continued to push it harder and harder trying hoping it would fire a code or CEL and to further diagnose it. Well, it did, gave me a blinking CEL and severe stumbling under any acceleration. I immediately pulled off and waited a bit. I started it up after a few minutes, had a solid CEL and found severe stumbling at idle and when trying to drive even in first gear. So I had it towed home, where I VAG-COMed it and got the following codes:

00280-Differential Lock Valve 2 (N126). Sporadic. Lower limit exceeded
00256-A/C Pressure/Temperature Sensor (G395) Sporadic. No signal/communication
00768-Rear Heater Core Temperature Sensor (G154) Sporadic. Upper limtit exceeded
00770-Coolant Temperature Sensor at Radiator Outlet (G83) Sporadic. Upper limit exceeded.

BUT NO MISFIRE CODES

So for the past two weeks, the car has been undriveable. It takes about 5 seconds to start up, idles rough, and the engine cooling fans run as soon as I turn the car on now, and increase in intensity after a few seconds. I've heard a bad thermostat can cause this (though I didn't get a code for it), so I went ahead and ordered a new one.

I went ahead and replaced the ECT/CTS immediately since it was so cheap and easy. However, I didn't think that little sensor going bad could cause this big of a problem, so I wasn't too disappointed after I replaced it and still had a car that can't get on the highway. My thermostat should be here in the next couple of days, but I have doubts about it solving the problem as well.

I searched high and low about the differential lock valve code, but could find nothing about it on forums or google. I'm not sure if it could cause these problems either, it doesn't sound like it should be directly to these problems. Does anyone have any idea what could be going on? I haven't checked the Cam Follower for wear, but it doesn't sound like that's the problem either. I'm just lost now after searching for weeks and still have no good leads to diagnose this ENORMOUS HEADACHE.

Thanks in advance guys, sorry for the novel^

[DRAKLORE]

My first inclination was the PCV, but that's been taken care of.
You never mentioned if you replaced the DV, which is next on the list of items to check and replace
The CTS has been an issue, but I would also be suspicious of the follower which could be causing fueling issues if its bad enough, pull the dipstick, smell for fuel. If the level is high and the oil is contaminated than your HPFP seal is bad ( I had this issue with very eerily similar problems)
CPS- but that would cause a no start...
Good luck

[andyisgood]

having the same problem... subcribed

[Boone]

My first inclination was the PCV, but that's been taken care of.
You never mentioned if you replaced the DV, which is next on the list of items to check and replace
The CTS has been an issue, but I would also be suspicious of the follower which could be causing fueling issues if its bad enough, pull the dipstick, smell for fuel. If the level is high and the oil is contaminated than your HPFP seal is bad ( I had this issue with very eerily similar problems)
CPS- but that would cause a no start...
Good luck

Thanks Draklore. I'll check the Diverter Valve for wear and tear. I haven't smelled fuel on the dipstick but I definitely will check the follower, as I'm pretty sure the previous owner was clueless on audi maintenance.

[camfahey]

similar problems.. mine was the engine speed sensor but it threw a code for it.

[Boone]

I checked the diverter valve today. Everything there looks good, no tears or dry-cracks. So I'm ruling that out. Still have to check cam follower but I have my doubts on that as well. If it was causing serious problems, it would be the HPFP and should have thrown a low fuel pressure code or something. Will keep you guys updated

[steven_1104235]

First thing I would do because of the number of codes; check your engine fuses in the ECU box in the engine bay. I just had an issue with 4-5 codes and after spending almost $200 in sensors nothing helped. Finally checked the fuses, and one was burnt. Easy to do after ripping the wiper arm off to access one of the cover screws, and then you can rule that out. It's a long shot, but it's free.
Good Luck

[Boone]

UPDATE: Checked the ECU box, everything is good in there. I replaced the Purge Valve and Fuel Filter, which both probably needed replacing anyway, but it made no difference. Today I'm replacing the cam follower. I should know then if it's a fuel pump problem or not. If so, I can spend another $350. Then I'll be replacing the Thermostat soon as well. I'll let you guys know how it goes.

[DevilS4]

If you end up needing a pump, pm me I have a brand new in box OEM one I was going to replace before I ended up swapping in the 2.7t.

[Shanster]

Boone, what's your transmission? Are you fwd?

[Boone]

@Shanster, it's a manual and quattro.
@DevilS4- I do need a pump, but Audi is covering it. I took the pump out Tuesday to check the follower and sure enough, it was worn through completely and almost fell in pieces as I took it out. Nasty thing. It caused some pretty good scoring on the cam lobe and ruined the plunger on the pump. I called Audi today and am having the car towed to the dealer to have the pump, follower, and camshaft replaced under the extended warranty. I had to fight with them using the warranty numbers from the TSB, so if anyone else plans on using this warranty, have it handy <http://www.awe-tuning.com/media/pdf/...FP_Upgrade.pdf> Hopefully the problem is solved when I get it back next week, it's just strange that it didn't throw any codes for low fuel pressure. I'll let you guys know then.

[Boone]

@Shanster, it's a manual and quattro.
@DevilS4- I do need a pump, but Audi is covering it. I took the pump out Tuesday to check the follower and sure enough, it was worn through completely and almost fell in pieces as I took it out. Nasty thing. It caused some pretty good scoring on the cam lobe and ruined the plunger on the pump. I called Audi today and am having the car towed to the dealer to have the pump, follower, and camshaft replaced under the extended warranty. I had to fight with them using the warranty numbers from the TSB, so if anyone else plans on using this warranty, have it handy <http://www.awe-tuning.com/media/pdf/...FP_Upgrade.pdf> Hopefully the problem is solved when I get it back next week, it's just strange that it didn't throw any codes for low fuel pressure. I'll let you guys know then.

UPDATE: So after having the car back for 2 weeks now, I'm satisfied that the problem has been FIXED! It runs better than ever and Audi covered everything. Now if only they'd man up about the dipped headlights...