So after driving a few days with the lamba light off, it came back on and the same code is back P0116 and the fan runs all the time even when car is not hot....so I think it is time for a new thermostat and coolant temp sensor. But it's also due for a timing belt and tensioner, etc so here is my list of parts to order:

1. Timing belt (from IPD with DVD step by step instructions)
2. Cam lock took from IPD
3. tensioner for timing belt (this is the 2nd change and not done 1st time)
4. Water pump (on the old 850 that started leaking around 200k and I am told it's easiest to do along with timing belt)
5. thermostat (possibly the "80 degree" one if I can figure out what that means
6. coolant temp sensor

Eek this is scary so many things to do at once

Is there anything else I should add while I am at it? Other sensors I am missing or parts that I "may as well do while I am in there"? Fuel filter (for some reason that one scares me most I hate messing with gas)?

What about brake parts what's the lifespan there?

The timing belt is a little harder than the S Belt. Yours is a 1998, I think, so the tensioner is due, as is the roller. The water pump is a gamble at 140K miles, it could go any time after 180K miles and some check the bearings by trying to wiggle the pully end of the pump. If it moves at all, replace it.

The ECT and thermostat are different projects and are very easy to do. Just drain out about a quart of antifreeze after unhooking the expansion tank and use a T40 driver to remove the screws. Easy.

The fuel filter is not as bad as it sounds, so long as you don't light up a cigar :) Just do it after the car has sat for at least an hour to let the gas pressure lower. Then open the hood and push on the schrader valve at the end of the fuel line to let the rest of the pressure escape. Then crawl under the car and pull off the filter. Keep a rag handy to catch a little dribble of gas. MIJ even used chewing gum to plug the line from the front of the car!

The timing belt is tough. Lots of luck. I hope you bought some wrenches,

Klaus
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1975 164 w/174,800mi (Sold) 1995 850T w/91,000mi, 1998 V70R w/129,000mi

So if I replace the water pump during the timing belt replacement, do I have to drain the antifreeze again? Assuming I would rather not tackle this all in one day! And, it's our only car.

If you pull the water pump, you have to drain the coolant from the engine. That is also a good time to do a complete coolant flush.

I am going to cheat and have a mechanic do my timing belt, and I will fork over 3 hours of labor. Yes, it is expensive, but at least I will have an ASE with a lot of experience check all of the components. If Rule308 or fixit lived around me, they would have first crack!

Draining coolant from the block is easy, and for the temp sensor and thermostat, you only need to drain about 1 quart into a clean container. Then pour that back into the expansion tank (except for any dirt in the bottom).

Klaus
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1975 164 w/174,800mi (Sold) 1995 850T w/91,000mi, 1998 V70R w/129,000mi