Last weekend my 87 Vanagon suddenly developed a 3600rpm idle!  Found that if I disconneced the lead to the Idle controlvalve it imemdiately dropped back to normal 850rpm.  Would this suggest a valve problem or does that mean something else feeding the ECU is telling it to request 3600rpm?

Trying to decide whether I should replace the valve (a $150 experiment) or just take it to the shop for real trouble shooting.

Thanks,
Alasdair Crawford
87 Westy