I got myself a cable and downloaded Unidiag and connected to the ECU on my 156 2.0 Twinnie. The car has sporadic hesitation issues on light throttle at around 2000-2500 rpm. I set up Unidiag to realtime graph the voltage output from the exhaust oxygen sensor, started the car and went for a short drive. The engine was warm but had been sitting off for about 15 minutes.
The first thing that became apparent was that the O² sensor stayed 'cold' for about 30-40 seconds, which from what I have read is way too long. It's reckoned 8 seconds to get the sensor to 500º C, so I think the heater in the sensor is kaput or has a broken wire or some such.
What is weird though is once warm the voltage started to oscillate nice and quickly, but wave amplitude got really big, peaking at 900+ mV and less than 50 mV, occasionally going off the reservation and dropping below 0 mV and bringing up a momentary error message in the status line to that effect. The voltage swing stayed in this wide range for the entire 8 minute drive.
Unidiag throws up an unknown DTC 0x01173 with the explanation of a short circuit to ground (where else would it go
) and makes mention of the minimum signal going out of range - which I asume refers to 'drop past' 0 V. This message comes back when cleared
I also noted a DTC P0170 Fuel Trim Malfunction Bank 1, which I assume is also related and doesn't return when cleared and the engine is warm. But has returned at some stage during the day.
From what I have read, and I'm a complete newby to Bosch Motronic, being for many years a Bosch Mechanical (in my 72' W108 280SE) and CIS-E (late lamented 190E 2.3-16) guy- that dud lambda sensors have slower 'cross-counts' and smaller voltage swings (sluggishness).... which i don't seem to be suffering.
I'm starting to think air leak downstream drom the MAF. Any ideas?