Passat B5 1999 with 2,3 V5 (AGZ engine), 100000 km/62500 miles. Motronic M3.8.2 injection.
Have had intermittent problems during last year with very bad performance during acceleration first 2-3 mins when cold started, but not every cold start.
Replaced O2 sensor 6 months ago, slightly better but problem still there. Mechanic suggested trying replacing MAF sensor too, but hadn't anyone available.
Now: Needs 4-5 tries when starting cold, then starts reluctantly. Really bad performance first 2-3 mins, then ok but still not really good.
"Bad performance" means accelerator works like inverted. That is, when I press the accelerator on 2nd gear, the power decreases. When I release the accelerator, (some) power gets back.
The problem basically shows only with cold engine.
Gets these two faults now and then:
00561 - Mixture Adaptation 12-00 - Adaptation Limit (Mul) Exceeded00525 - Oxygen Sensor (G39)
27-10 - Implausible Signal - Intermittent00561 has not returned for a couple of days, 00525 returns more often.
In the "readiness" window everything usually looks ok except the last one, catalytic something...
I have tried cleaning the MAF with electronics cleaner, containing Isopropanol and CFC22. I have been reading about people using carb cleaner and other stuff, I'm not sure what chemicals I "dare" to try. A problem with my type of MAF sensor is that I can't see the platinum wire, so I don't see the effect of the cleaner, I'm just spraying the cleaner through the "intake".
Tried disconnecting the MAF, two starting attempts failed. Then I reconnected the MAF, and it started rightaway!
Repeated next day (cold engine again) this time one failed attempt with MAF disconnected, 2nd attempt with MAF connected, started!
But if I try with the MAF connected at 1st attempt, I need 4-5 attempts.
No error codes have returned for the last couple of sessions, but the catalytic... in the readyness window stills says error.
Does this make sense to anyone!?
Looking at the VAGCOM displays when running most things looks sane, including the two temperatures (coolant and, I suppose, intake air) and air flow ranges between 3 and 30 g/s.
The O2 value is ± 25%, but when idling it's ± maybe 2% only.
The ignition timing is about -30 degrees, seems like some misinterpretation by the program?
So, any suggestions are welcome. I have some VAG logs too.
Should I be looking for a new MAFS? Or should I be looking for something else? Could a bad MAFS really make the engine that hard to start only when cold? To me it seems like something else, maybe something with the fuel pressure?
Could the new O2 sensor have gone bad in just 6 months? Or is this an indication of something else?
Thanks for any input, Jonatan Lindell