orangedawg

Now, in case you are wondering why I am excited is because for the last 3 weeks my car has run awful (have to baby throttle to get it to 30 mph, hard start when cold, idles fine however). This occurred after fuel filter and tranny fluid change. Also, the CEL would not come on and car would throw no codes. However, today, it finally threw the above codes. Now, I SFTA and these codes are most commonly associated with a lean code and usually bad MAF. What I have done so far:

Immediately prior to poor running (ran well before this):
Changed tranny fluid/filter
Changed fuel filter

At this point, car ran poor as noted, so I changed:
MAF (per a number of suggestions here), no change, still ran poorly
Fuel pump (it was whining), no change but at leasts it's quiet now. Coincidentally, car threw these codes 24 hours after changing pump.

My plan:
1. Pull out MAF (this is the old one, not the new one as that was returned) and clean it with CRC MAF cleaner to see if that works
2. Change coolant temp sensor

Also runs better when warm, but still can't put throttle down more that 15% or so. I don't have a VAG, had Autozone pull these codes.

Is it possible that it still may be the MAF? I am also planning on changing the coolant temp sensor as the car is hard to start when cold, but easy to start when warm. Car ran fine prior to changing fuel filter and tranny stuff. Could it be another bad filter? Ideas? Thanks!

Slivka

<center><img src="http://www.urbanachiever.com/albums/slava/engine.jpg"></center><p>A crack in either of these can cause a lean mixture, which your codes seem to indicate. Happened to mine, although except for the CEL I did not notice anything.

ModifiedA4

i was about to post that the FPR hose is a likely culprit.

orangedawg

Do I have that hose on a 2.8 30v?

orangedawg

As suggested, I changed my fuel pressure regulator hose (on the 2.98 30v, it's on the driver's side and runs to the back of engine under all other vacuum hoses, correct?). Anyway, no change in engine running. Still runs awful at higher rpms (above 2500 or so). Oh, I also cleaned MAF with CRC MAF cleaner and no change in car running occurred. Any other ideas?

Shard7

The FPR is vacuum controlled and it reduces pressure if there is a higher vacuum (and hence the engine needs less fuel).

One thing worth trying is to disconnet the vacuum hose from the regulator and plug the hose, then see if the engine will go up to a higher rpm without sputtering.

Another helpful trick would be to plug in a VAG-COM and monitor some of the sensor values while all of this is going on. It'd be interesting to see what the ECU thinks is going on.

Let me know if you're by chance in the Chicago area, I'd be up for giving you a hand if you need it.

orangedawg

Weird thing is this all happened after changing fuel filter and tranny filter. Used my ebay cable and shareware VAG software and my laptop fried after that. Can ran perfect before. Think it may be ECU, but car runs fine at idle and very light throttle. If ECU was out, I assume car wouldn't run at all. And today was first time a code threw (it's been running like this for 3 weeks). Shop is stumped as well. Says to try coolant temp sensor. Maybe new fuel filter is bad? Cdoes thrown say bad MAF and o2 sensor. But since it's both banks, 1 and 2, I ruled out o2 as it would be really weird for them to all go out at same time. Unless new MAF is bad as well?

Shard7

Modern ECU's are really good at detecting bad sensors, there's a lot of software in them specifically to validate sensor values and perform tests to make sure they're operating correctly. If a bad sensor is detected, you'll get a very explicit code and the ECU will try to get by without the sensor (it'll ignore the erroneous values and make do without them).

One thing to remember is that a code is set when a problem is detected in part of the engine management system, not the entire engine. The ECU won't set explicit codes for things like bad valves, clogged filters, sticking pistons rings etc. So don't assume you'll get a code that pinpoints the problem, and good old fashioned engine diagnosis may still be needed.

Besides the FPR, checking the fuel filter might be worthwhile. I highly doubt that the new filter would be defective, but there is a good chance that installation was incorrect. Is it installed backwards? Did something fall into ports that is now clogging the lines?

As I mentioned in a previous post, doing a fuel flow test would tell you a lot. Pretty simple to do, and much cheaper than replacing lots of parts and sensors.

orangedawg

let the engine run? After I did the fuel filter change, it ran fine the rest of the day. It was the next morning when it ran like it does. I've been dealing with this for 3 weeks and still can't figure it out. And my laptop fried shortly after hooking it up to car using ebay cable. Could it have fried my ECU? Again, it ran fine that day after the laptop fry/filter change. It was the next morning when it ran poorly.

Shard7

that it's a blockage in the fuel line. A pinched line or bad filter would have caused the problem to appear right away. But suppose something got into the fuel line (maybe a loose piece of filter media or other contaminant) and slowly worked its way into a tight spot in the fuel line. That would explain the fuel starvation, and would also explain why your old fuel pump was making lots of noise all of a sudden.

Like I said, checking the fuel flow at the injector rail will tell you a lot.