Code P0300 - Random misfire troubleshooting - Bad MAF?

[jarhead26]

Hey guys, have a 2008 Audi A4 2.0T Quattro that is throwing codes P0300, P0302, and P0303, and misfiring, mostly, at idle.

Originally, my CEL came on with code P2177 - System too lean off idle, Bank 1 and P310B - Low Fuel Pressure regulation. After some research, I replaced the MAF, Diverter Valve (cause I had an extra one lying around), checked for vacuum leaks, and tightened intake hoses. After, the codes went away.

About a week later, the misfire codes popped up. I changed out the spark plugs, coil packs, and cleaned the air filter. After replacing these, the codes still show up and I get some pretty rough rumbles on idle.

When I check channel 15 and 16 on my OBDEleven it'll show most misfire counts in cylinders 2 and 3, but I'll occasionally get counts for 1 and 4 as well.

1. I bought a cheaper MAF sensor ($60) that was made in China. Could this be a culprit and I need a VW/Audi replacement?
2. Any other idea why I would be getting misfire across all cylinders, but mainly 2 and 3, if it's not the MAF?

[jarhead26]

Update: I drove to the store and when I came back out and fired up the car it started idling erratically. It was about half up to temp. The RPMs dropped to about 500 then shot up to 1300. It leveled out, and then did it again about five more times before finally settling at normal idle. It then threw a CEL.

It's now showing code P2177 - System too lean off idle again. All in all there are codes P2177, P0300, P0302, and P0303.

Could bad injectors be causing the combination of these codes?

[Older_not_Wiser]

Injectors is a possibilty, but I had a somewhat similar issue, but it included occasionally dying while sitting at a light idling, the RPM sometimes dropping to 400 and then up to 1200 or so.

I had flap motor codes too along with too lean off idle and sometimes multiple misfire codes. Sometimes during cruising/steady throttle I would get a momentary buck from the motor.

I did a lot of logging of fuel parameters and noticed sometimes that the rail pressure would spike 10, 20, sometimes 30 bar over requested for a short period of time then come back near requested. It would do this at idle, cruising, but never saw it at WOT.

The injector timing scaled down big time when the rail pressure spiked, which I guess makes sense due to the rail pressure and probably was the reason for the dying while idling at a light. The injector timing went to essentially zero at that time.

So bottom line, I kept doing a lot of logging trying to capture data when is was occasionally doing the hiccup/rail pressure spike thing until I finally caught a few hiccups where the RPM logging signal showed zero for one beat a couple of times.

I replaced the crank sensor and all was back to normal, so the take away is, try and do a bunch of logging different parameters and go over the data. I was getting flap motor codes, misfire codes, and occasional bucking and dying and I could have replaced the flap motor and injectors and it would not have fixed it. It was a fricken crank sensor.

Not sure this helps you a lot, but keep logging and it should give you some answers. You could also look at the fuel trims. That might tell you if the ECU is trying to add fuel signalling a clogged injector(s).

[Theiceman]

really not sure why you are swapping all those parts for nothing when in your first post you literally told us the car has low fuel pressure...

wouldn't you start there ?

[Marques1]

That would make too much sense :o

[jarhead26]

really not sure while you are swapping all those parts for nothing when in your first post you literally told us the car has low fuel pressure...

wouldn't you start there ?

That's fair. I guess I was stuck on it being an air issue. Where would you start then? Fuel filter? Fuel pump?

I'll check the fuel trims as well. It sounds like the crank sensor could cause low fuel pressure?

[Theiceman]

there are guys on here really good at fuel.pressure issues so I will wait for them to chime in. but I know lpfp duty cycle is important and fuel.rail pressure , both of which you can log.
running lean is either too much air or not enough fuel, and you car is telling you not enough fuel.

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[Jayz691]

If you think ya have a fuel issue, id start with logging blocks 230 and 231, thats high and low side pressures. Also, look at block 32 for your ltft's, has both idle and partial throttle. Can also watch block 33 for instant(stft) value. See if either side is not meeting requested, lpfp duty %, and if either of your trims are way off. Report back.
Just a fair warning, fuel issues can be a real PITA to figure out on these cars.

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[jarhead26]

It's starting to show how much a pain it could be.

I just got a new fuel filter cause I figure I haven't changed it since I've bought the car, which was 100k miles ago.

This morning, I had a new code pop up - code p0507 - idle control system higher than expected. My engine is now slowly increasing RPMs to almost 2000 and then dropping them back down to about 1100. It tries to hold at 1400 or so, but keeps fluctuating and will sometimes drop out to about 400 RPMs.

I'm not sure if the channels are different for VCDS and OBDEleven. Channel 230 on OBDEleven was showing my commanded fuel pressure, which was at 50.00 bar at idle. The actual fuel pressure was fluctuating a bit, between -1 bar and +1 bar. The screen shot I took had it 1.08 bars lower than what was commanded, but I did see it jump to nearly 1.5 on a few occasions.

Channel 231 showed Fuel at around on the first line at 4.55 bar and on the second line at 4.58 bar.

Channel 32 was for the oxygen sensor and showed lambda actual value at around 6 to 7%. Channel 33 had a bank 1, control value at 23.00% and a bank 1, oxygen sensor voltage at 1.00 V. Nothing for bank 2.

[jarhead26]

So I replaced the fuel filter and this fixed a lot of the misfires and idle issues but did not eliminate the misfires in 2 and 3 entirely. All 5 codes are still present but when I check the live data I only see misfire counts in cylinder 2. They are also only present on idle from what I can see.

The boost feels much more responsive, but still has a small hickup maybe half way through the uptake of the pull.

Would a bad injector cause idle control problems and lean issues? And is there a way to test them without pulling the intake?

[Jayz691]

Yes, the blocks are the same.
If your "idle" ltft is at +6-7%, id say you most likely have an air leak(Assuming its not .6-.7%). Or, for some reason, it's not getting enough fuel, because the ecu is adding fuel. And with your stft's up around 22%, its almost at max correction at that instant. Your fuel pressures are good at idle, but without logging, can't really know how they are throughout the rev range. But since ya have obvious issues at idle(fluctuating), id start with some pressure/smoke testing of boost/vac lines. Also, hows your PCV system? Bad PCV or check valves, can cause vac leaks.
There was a VIN split, so make sure you have correct PCV/rear breather paired. Check your rear breather pipe for a check valve. If it has one(black tip), make sure it seals properly from Turbo side. If it don't, check you have the correct PCV(revision N/R) to go with it.
The new "idle control" code is because of your ideal issue. Its an effect, not a cause.
Could also be an injector or bad 02 sensor, but start with the stuff that is cheap/free to check, before buying pricey parts.

Next time you check you fuel trims, post a screenshot.


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[jarhead26]

To close the loop, I eventually took it to a German car specialty auto shop. They confirmed that the fuel injectors and dirty valve covers seem to be the culprit. The top of my dipstick has been broke for some time as well. I thought the seal worked just fine, but they said it could be causing a vacuum leak from there too.

The CEL hasn't come back on, but I still get passive misfire codes on the OBDEleven. Misfire counts only happen on idle. Top end boost likes to kick out, but if I stay away from it, the car drives just fine. I'll be replacing the fuel injectors soon.

[Jayz691]

Report back with results. Hopefully it fixes it..

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