2.0 TFSI random misfire

Old 07-07-2019, 04:07 AM
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Default 2.0 TFSI random misfire

I have a 2010 A4 Allroad 2.0 TFSI with 120 000km on the clock. About 3-4000km back I changed oil, filter, sparkplugs and coils.

But before that the car would suddenly hesitate and start shivering (misfireing, limp mode?), this only happend 2-3 times during about 6 months and would only last for a short while (like 5-15 seconds) then clear up by itself. Can't remember if the CEL light ever came on either.. maybe once but I never got any fault codes.

This led me to put new coils in when I changed the plugs (plugs where due for the 120 000km service). But a couple of weeks ago it happened again, only this time it didn't go away until the engine had cooled down. I drove it gently for maybe 10-15km like this just to get back home. This time the CEL light came on and stuck on, ESP light also came on.

So I plugged in my bluetooth OBDII reader and checked for codes in the Torque app on the phone. Only code I had was misfire on cyl 4. So while the engine was cooling off I swapped the coils on cyl 3 and 4, it took a lot longer than usual on the starter before it powered up but once the car started the engine ran nice again. So I took it for a testspin with the phone app logging everything it could and when I got back I didn't have any new faultcodes. But I found a value called "EWMA misfire count" in the log that stated that I'd had a number of misfires on cyl 4.

But the car still ran good, and I didn't get any fault codes.. About a week later it once again started shivering, but corrected itself after maybe 10 seconds.. no fault code. Of all the times this has happened, it's never happened directly after a cold start. Twice it has happened with the engine truly at operating temperature. And all the other times after maybe 4-6km of driving from cold start so more or less warm.
The only thing I've noticed is that the fuel consumption is a bit higher than what I would expect, but then I've got 255's on it so that might be the cause there..

From what I've read the most common culprits for this issue are in decendeing order:
Vacuum leak
Carbon build up

Out of these the first two should be the problem. The last one should cause problems during cold start before problems accure when warm? An injector feels far fetched.. Is it really common for these to fail after only 120 000km? Vacum leak is possible, are there any common vacum lines that are prone to crack on these that I should start by checking? And with the MAF, if that's the issue It should be all the time, shouldn't it?

Since the issue is so random and won't leave fault codes (atleast none that I can read, are there any VAG com stuff for DIY mechanics that read more info than other?) I'm not very keen on sending it to an Audi workshop.. Atleast not yet. Does anyone else recognize these symptoms? Have I missed something ion my list that could be the issue?

Or should I first get a better OBDII reader? If so, which one? Is Ross Tech still the best one out there for DIY'ers?
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