A4 Quattro 2.0T-stalling/surging no codes

[Dutch^]

Hi, I'm at a loss, and could really use some help. This car had a used engine swapped into it and came to me running in limp mode with the Maf sensor connector disconnected.

After replacing a few parts, I have alleviated a few codes I was getting, but the car still will not run properly.

I was originally getting P0008 and a Maf sensor code and one other that I can't recall now. I replaced the hpfp, low fuel pressure sensor.

I now get no codes with the Maf sensor connected, but the engine tries to stall in idle roughly every 5 seconds, surges to recover, then returns briefly to idle ~800-900 rpm. Then it repeats. Occasionally it'll stall completely.

I get no codes now, I'm so frustrated with my first Audi experience! Please help if you can.

Thanks,

Jon

[shahk62]

Have cleaned the intake manifold & tried running an injector cleaner?
You may have some carbon buildup in the intake flap motors which is causing some issues


Sent from my iPhone using Tapatalk

[Dutch^]

I have not, I will give that a try. Thank you.

Further info: I was able to drive it home at freeway(70) speeds, though it took longer than any car would normally take to get to that speed. The power was steady at that speed. Also, I have since changed the fuel filter after that

[Dutch^]

I assume by intake flap motors you mean throttle body?

[Dutch^]

No difference. It idles fine if I disconnect the Maf, which I suspect happens because it's automatically put in limp mode. I did try a new Maf sensor just to verify it isn't the Maf. I only get Maf codes when it's disconnected.

[mgfranz]

No difference. It idles fine if I disconnect the Maf, which I suspect happens because it's automatically put in limp mode. I did try a new Maf sensor just to verify it isn't the Maf. I only get Maf codes when it's disconnected.

Does it have a new pressure valve? (CCV, PCV), whatever you want to call it. Mine did what you describe in your OP, changing the valve solved the problem, code thrown was a 0171 or 0172, don't remember exactly. Don't use a cheap one, go ECS or OEM. What about fuel filter?

[pezgoon]

Are you SURE there's no codes? As in, have you checked it with a legit Vag-com cable? Not all codes cause check engine lights (although any that cause surging should) and not all code readers can read Audi's codes'

Any idea how many miles are on the used engine?

[Dutch^]

Thanks for the replies. There were a few codes, related to fuel pressure. The new hpfp and low fuel pressure sensor that is mounted on the pump alleviated those codes. The first thing I changed was the fuel filter. I have not yet changed the PcV valve.

The reader I'm using is an Ozzy obd2 Bluetooth enabled reader: OBD II Bluetooth Diagnostic Scanner by Ozzy Gear-Read Car Engine Codes, Reset Check Engine Light-Features On/Off Button-Lifetime Warranty-Android Only https://www.amazon.com/dp/B00YY7M4AO..._Tc6XxbHH832TG

I can't say for sure that my reader isn't missing possible codes. I can't say for sure at this point in time how many miles were on this engine. It took 3 engines before they could get one that ran. It was I thought sort of a favor from a friend that owns a scrap yard. Disputes between the shop and my friend about having to reinstall it twice.

The battery was totally dead at one point. I read there is a throttle body setting that needs to be reset in a vag com since the battery was disconnected for a couple weeks. Might this be part of the problem. I will replace the PcV valve. Is that the one on the head above the intake manifold ?

Jon

[mgfranz]

If the PCV valve was bad, you would get a simple P code from your reader, but your reader will not pick up diag codes that are stored in the ECU, you need a vagcom cable and VCDS.

[Dutch^]

$400ish? That's a tough pill to swallow. I may end up biting the bullet, but this car is getting tougher to love by the minute

[Dutch^]

I ordered a new evap purge valve and PCV valve. I managed to snap off the 90° vacuum elbow that the purge valve joins to :(

[Dutch^]

Okay, I am still having issues. I installed the new PCV valve and purge valve. The PcV valve was completely missing a check valve, so obviously it was contributing to the problem. I wanted to post a picture, but I'm clueless.

After replacing those items, the engine was now idling poorly, but not surging, so I checked, and realized the Maf was unplugged. I plugged it in. The idle smoothed out. A test drive showed it was under powered, but better than before, probably still in limp mode. I headed home to read codes. The code indicated Maf circuit malfunction. I reset it while it was actively idling smoothly. Immediately the surging and near-stalling returned. It was idling fine until the moment I reset the codes! So I turned it off, restarted it, then checked codes..... None.... But it's back to its original problem, even though the problem was gone while the code was still in the computer....I am so frustrated.

The car has now been sitting a total of about 3 months. Maybe bad gas is contributing. I'm going to fill the remaining 3/4 of the tank with high test to see if it helps. I don't know what else to do.

Any comments are so welcome

[mgfranz]

Okay, I am still having issues. I installed the new PCV valve and purge valve. The PcV valve was completely missing a check valve, so obviously it was contributing to the problem. I wanted to post a picture, but I'm clueless.

After replacing those items, the engine was now idling poorly, but not surging, so I checked, and realized the Maf was unplugged. I plugged it in. The idle smoothed out. A test drive showed it was under powered, but better than before, probably still in limp mode. I headed home to read codes. The code indicated Maf circuit malfunction. I reset it while it was actively idling smoothly. Immediately the surging and near-stalling returned. It was idling fine until the moment I reset the codes! So I turned it off, restarted it, then checked codes..... None.... But it's back to its original problem, even though the problem was gone while the code was still in the computer....I am so frustrated.

The car has now been sitting a total of about 3 months. Maybe bad gas is contributing. I'm going to fill the remaining 3/4 of the tank with high test to see if it helps. I don't know what else to do.

Any comments are so welcome

Have you changed plugs yet?

[Dutch^]

Thanks for sticking with me.
I haven't yet. I asked that that was done when the engine was swapped, but at this point I don't have a lot of faith that anything I asked for was done, including new timing belt and components. I'll check them.

I'm leaning towards it being a vacuum leak somewhere.

[Dutch^]

Oh, I forgot to mention. I drove it to work last night. If I very gradually increase the throttle, I get past the heavy surging, and after getting past it, it mostly goes away, even in idle. But if I send a clear signal to the ecm it immediately begins the heavy bogging and surging symptoms again. I also found that after getting enough normalcy in how it's running, and can rev the engine higher, it throws a code ( I think p0299 ) indicating a turbo bypass valve failure. I have that on the way now too