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Why 200 rpm more? I keep wondering.
I decided to google something like "950 rpm idle Volvo" and found a thread about an auto in D or N. OK, so the auto in gear drags the rpm down enough to compensate that beforehand. Same thing with the A/C.
But I have neither and I made sure that those pins on the ECU were tied to ground. Or at least I was kind of sure, so I went over it again using TP 31361/1.
Did I say that unused signals are tied to ground? Well, with manual transmissions pin 30 should be tied to ground. Confirmed that.
Now what about the A/C pins 14 and 15?
I don't have an A/C, so I assumed they would be tied to ground to simulate an A/C that's switched off. Unfortunately, TP31361/1 doesn't mention cars without A/C. Just that pin 14 should be about 0 Ohms to ground and pin 15 1kOhm to ground with the A/C switched off.
In my case there was infinitely high resistance between pin 14 and ground and 15 and ground.
I had already meaured voltages on these pins close to .2 V or so during driving, so I thought I had eliminated that as a possible cause. I assumed a pull down resistor internal to the ECU would take care of an unconnected A/C.
Now I have run a wire from pin 14 to ground to make sure that is pulled hard to ground at all times, simulating an A/C compressor in the off-state. A first test drive was successful, but I won't draw any conclusions just yet. Time will tell...
To be continued.
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