my (haines) manual tells very little about tune up on my 89 240. B230F
it has an air mass meter measuring the air intake , and there is a air
control valve underneath the intake manifold. in the book I have it
shows the air fuel mix being adjusted by a screw on the air mass meter
, but mine has no such adjustment.

I just finished rebuilding the engine. new pistons etc. etc. etc., the
works.. it is in fine shape , mechanically, but still it failed the
emmisions test.

there is an switch on the on the throttle body and it seems to
influence the air valve. I adjusted it a little to make sure it is
closed and that just made the car fluctuate at idle.

I would appreciate it if anyone can point me in the direction of any
good info on the subject, or fill me in on how the system works.
what can I check with a meter? or a scope? is there a screw somewhere
to adjust airflow or something?

also I have heard about reading the fault codes, and would like to
learn more about how they work.

I can and will have my experienced volvo mechanic look at The car , he
is great. Still , I like to do almost all my own work on my 122 ,
244 and 245 and we have a bunch more volvos in the family, so it would
be nice to learn a little more...

thanks, Phil