Volvo Repair: 1991 volvo 240, volvo 240, diagnostic port

Question
the chk engine light has come on & the engine sometimes tries to rev up while i'm at a red light & have my foot on
the brake. My son found a small hose that had a hole in it,
& replaced it & then the light went off, but came back on
the next day.  How can the codes be checked to see what the problem is.  My son can do the work if he knows what's wrong.   Appreciate your help.

Answer
Liz, he has to read the codes. Have him go to the diagnostic port and read on number 2 first.  Key on, hold button for 10 seconds.  Read flashes.  Example, 1-2-1, then  write it down.  hold button for 5 seconds and read again.  Read until the first code that was read comes back up.  Then hold button for 10 seconds again until red light stays on.  When it does, hold again for 10 seconds.  Check engine light will go out.  Have hime do it on port 6 also.  REad codes and let me know what they are.  We can go from there.  Roger