Hi,

https://www.brickboard.com/RWD/volvo/1670769/220/240/260/280/long_crank_warm.html

I remembered seeing this in a recent thread for a “hard warm start” situation.

Do both sensors have the same color of plastic socket?

Note! that this is a graph for checking out the ECT from the ECU pins, that’s in the cabin behind the right side kick panel.

I’ll question the 50 degree reading that you presented.
Was that from say both laying on a work bench?
Or is one inside a cars coolant and the from one just taken from inside that tool box that is in the same garage environment?

There are two different ones used in these LH cars but the chart applies to all years.
Make sure they match the year car!
As far as I know, this chart is what all the ECU’s have as a working range to work in.
What each ECU does with the information is what is built later into their programs.

You can be looking at a misfiring cylinder more than a mixture issue in lots of cases.
Alway suspect ignition issues first on things of age!
The LH systems try to compensate, very quickly, by adjusting several things simultaneously.
The idle speed is when it’s the slowest gap between adjustments.

Vacuum leaks behind the AMM is just as likely with age.
Square away ignition system and move on with checking out the accordion hose and hoses connecting to the throttle body.

At low idle speeds the AMM and the Oxygen sensor work hand in hand, as this is the only way the ECU can tell what’s going on.
The ECT is just another player to tell the ECU where the engine is and what mode it’s running in.
There is start, warming up and up to operating temperature.
Mileage depends on all three with good spark delivery!

Post back what you have going on, we like puzzles here on the forum.

Phil