So, my 2006 A4 2.0Tq needs a thermostat. I am pretty certain of this as it's not coming up to temp and has a P2181 code. I've been driving it for a couple weeks like that because I just don't have the time or money to deal with it yet. I don't think that's related to this new problem, though.

I went to start it up the other day and it shuddered and bucked, flashed a CEL at me, and I shut it off quickly. Pulled the codes and the new ones are P0089 (fuel pressure regulator/sensor) and P0304 (misfire, cyl 4).

A few questions:
- Is the misfire just a result of the fuel pressure problem?
- What do I need to replace? Is it a fuel regulator or a fuel sensor?
- Is it worth pulling the HPFP and checking the cam follower with this code or does that cause different codes (I see conflicting messages in various forums)?

Any help would be appreciated. I'm not a genius mechanic, but I can turn a wrench, so if it's something I can save hundreds by doing it myself, I may try. Closest dealership is 20 miles away which is a heck of a tow bill. Plus the ridiculous premium they charge (they quoted me $500 for the thermostat alone). I've done a bunch of searching, but haven't found anything conclusive here or at other Audi forums.

 

So, I'm pretty stumped on this one. I had it towed to a local indy mechanic (not an Audi expert or anything) and he said the computer needs a reflash according to one of the codes. He also swapped the coil packs on 1 and 4 to see if the misfire code follows the coil. It seems to be running fine now other than the thermostat code popping on and off. In fact, the day I had it towed, I drove it out of the garage and up my driveway to the tow truck, so it was pretty much running fine then as well.

The only thing I can figure is that the one time this happened (rough start, running rough, and the P0089 and P0304 codes) it started up oddly. I usually turn the key to ON for a second so the fuel pump can prime (you can hear it when it turns on) and then start it. That time, I didn't and the key slipped out of my fingers before the car started. I immediately twisted it again to start it and that's when I had the trouble. Maybe it was a fluke due to the way I started it? Seems pretty odd, though.

I'll update the thread if it comes back or if I learn anything new.

 

I'm having a similar issue, without the misfire, one person suggested high pressure fuel pump, my pressure regulator has already been replaced. My in tank pump has been replaced along with the pressure regulator prior. I've ordered the cam follower it's cheap to try.. Not sure if it will work. I have a new issue, kind of a rattling noise when idling in gear with the brake on, may be a motor mount.

 

It's probably your low pressure pump (in the tank), but without more diagnostics, it's hard to know for sure. I'm about to get the second one put in tomorrow after the first replacement started dying after about 6-7 months. I really hope that fixes it.

I went through a LOT to make sure it wasn't the HPFP, but it really wasn't. I had Audi diagnose it for $150 and then after I didn't believe them that the LPFP was bad again, I paid them another $100 to pull the HPFP and cam follower and check them. They're fine, so it really seems to be that low pressure pump again.

It seems P0089 is a very generic OBD code and Audi has the ability to pull more useful codes with their scanners. They reported a P0310B and their GFF test pointed to the low pressure pump, so I guess that's it. It just surprised me a lot that it went bad after only about 7 months.

In my case, the misfire seems unrelated. I had a coil pack replaced a few months ago, so maybe it was that.

 

King I had the exaclt same thing happen to me (minus a code). Key slipped before the car started and when I restarted it ran horrible. Backed it out of the garage and shut it off. Say there for a minute and restarted the car. Ran fine from that point on.

 

Exactly! I guess I'll never know if it was the coil pack that went bad or just that key slip. Either way, it hasn't done it to me since.

Now, if I can just get rid of the P0089 and the LPFP issue...