Hi,

I’m a 240 series man but I shop other tabs here on the Brickboard for a widened entertainment experience. (:-)

Why are you idling the engine that long? 15 to 20 minutes is not a good thing to do to any engine let alone wasting the gasoline.
If the car is not warmed up long before all that, you probably have a failed coolant thermostat.
Does the inside gauge work?

If the engine is not warming up idling that long can foul the sparks plugs and not do the exhaust system any good either. The list for cold engine problems goes on!

As far as what brand is good in the OBDII diagnostics, I can only recommend an ACTRON brand as I inherited one from a neighbor that had passed away.
He had newer 2000 to 2006 vehicles. He got it from J.C. Whitney catalog sales. He used them a lot, not that is a reason to use them, but we have limited resources where we live.
Also, He was rather frugal so I guess it’s priced mid range for him to buy it.
This OBD II reader unit came with oxygen sensor tester lots of books and disc for desktop use in one big plastic case. I suspect it was a close out from the catalog sales company.

It spits out a direct code number so no need for a computer even then and is a lot nicer.
My older OBD I system, prior to 1996, is built into the my cars with a red flashing light to count. So I use it on other peoples or a relatives cars!
I recently help fix another visiting neighbor car.
It was a 2014 Honda that had a code for a MAP sensor.
I look up on the codes on the Internet’s You Tube University for a fix.
Turns out had that code due to so many ash ridden wildfires.
Washed it down a little with a spray.
So, at least this brand doesn’t go as obsolete as others I have noticed in some of my reads!
Nowadays, with these items you get what you pay for and that depends on how much you know or how capable you are to fixing vehicles.

A 1997 is not overburdened with tons of computing garbage. Most any code readers will cover this car and since they are better now, will work on any newer cars that you end up getting later.
Being a “mid range buyer” is the best course to take no matter what decade you are in!
Volvos of past have always been slightly above mid range but that why they are still on the road.

I’m not saying anything about the newest car technology trends no matter who you pick.
It all going to change!
I hide out and watch from my 240s and saved myself from a mess of depreciation in values with in all the electronic gadgetry! I have benefited from the “others” cast asides!
Maybe much like you!

I hope this gives you some guidance and that others with your type vehicle will post help that’s more specific.

Phil