jhoeppel

<i>I usually post on the TT forum but my daughter's '00 A4 1.8t has started acting up...</i>

Symptoms: at higher rpm's, engine will run stumble, run roughly, lose power, and may -or may not- turn on the CEL momentarily. There appears to be no symptoms when the engine is cold, and therefore running on the built-in default ECU maps.

Before testing it, I scanned it with my ProDiag and found these faults.

17522 P1114 163
Bank 1 - Sensor 2: internal resistance too large [Sporadic]

16795 P0411 163
Secondary Air Injection System: Incorrect FLow Detected [Sporadic]

While data logging during a full throttle run in 2nd gear, I noticed the air mass reading climb up to about 120 g/s at 5000 rpm, then abruptly drop to 65 g/s, then up to 213 g/s... fluctuating from 70 g/s down to 7 g/s... all in 5 secs, before I lifted off the throttle. During these readings the car ran roughly with no power. After a few moments, it settled down and I was able to drive home gently without other symptoms...

A scan following this run added the following fault codes:

16486 P0102 163
Mass Air Flow Circuit -G70: Low Input [Sporadic]

16684 P0300 035
Random/Multiple Cylinder: Misfire Detected

16688 P0304 035
Cylinder 4: Misfire Detected

16686 P0302 035
Cylinder 2: Misfire Detected

<b>So, what's the diagnosis?</b> Bad MAF? Could this be linked to the original sporadic 02 sensor problem?

TIA, ~john

ModifiedA4

fyi, from what i know the ecu doesnt use the second 02 sensor for much...its an emissions thing.

also, there is a procedure in the bentely manual for checking the maf. the readings at idle and a certain rpm are checked, while parked.

the ATW engine doesnt like vac. leaks, so recheck all the vac. connections on the engine.

here's a pic of the electrical stuff under the coolant tank:
<img src="http://www.modifieda4.com/images/oil-cooler/DSC00495.sized.jpg">

audichopper

I know your post says oppisite but your discription sounds almost identical to what i had. Sometimes idle so rough it would almost stall. My 2000 A4 1.8t did this as well and it was the secondary air pump was bad. Litterally split all the around at the rivets. My Audi tech said it is a very common problem and should only affect the car at start up for a few minutes and then run normal. There is a measuing block to do a secondary air pump test, i want to say something like measuing block 77.

jhoeppel

Car runs fine on a cold start, but there is a start up noise that some mechanic told my daughter was the 2ndary air pump. They've also had thermostat problems and I thought it took too long to warm up.

Other than the noise, the car runs smoothly when cold, and revved up smoothly to maybe 4000rpm when the temp was only reading 60C +/-. It's only when more fully warmed did I do a full throttle run and encounter the problem. Son in law reports that she only drives maybe 10-15 mins to work, so maybe it's not really warmed up much of the time she's in it.

Thanks on the measuring block 77 tip. I'll check it next time I get a chance.

~john