I've been getting poor mpg on my '85 244 lately and aware that the O2 sensor had to be at least 15 years old I thought I had nothing to lose by replacing it. I soaked it with PB Blaster for about 2 days and meanwhile checked on O2 prices. The Volvo stealership wanted $400+, IPD $100+ and Autozone $62...all for the same Bosch 13957, 3-wire. So I went to AZ, bought the sensor, they loaned me the special socket, the old sensor unscrewed easily, and the new one went in. The old sensor's tip that lies in the exhaust stream was coated with soot indicating the engine had been running pretty rich. MPG has improved dramatically and the idle, which was fairly smooth before, is even smoother.

...thanks Autozone.

Dukester