Volvo Repair: overdrive problem and fast running, relay switch, idle air valve

Question
Hello I have a 1983  240 with only 67 000 km on the clock its a
GL model and runs like new. I have a problem for time to time
when the o/drive  will not engage;  I push the switch in and out
and it shows on the dashboard then for no apparent reason its
goes in.
Another thing also it appears to idle at 1000-rpm which for me
is to fast  should this be about 700.
Ant Ideas.?
Steve

Answer
Overdrive is simple circuit. Three parts make it work. od relay, switch and harness, and od solenoid at transmission. First thing to check is od relay sitting behind glove box, it sometimes stick and will not click. Replace or repair. Next problem is switch and harness. Don't know if this is stick or automatic, different procedure for both.

High idle, check the idle air valve circuit, may be sticking, tap it, if idle goes down, may need new one