The idle on my 86 420 SEL seems to be hunting. It will speed up to 1800 rpm, and stay there. After a while it will return to normal, but then do it again, even as I'm driving along. When this happens the SRS anti lock light also comes on. It is an intermittent problem, but can be dangerous, as I never know when it will happen. If not careful when in traffic, the added rpms can cause the car to lunge forward. Any ideas?