1999 Ford Explorer XLT 4.0 SOHC-For several months I have been experiencing a slight bucking between 35-40 mph, and rough idle when I'm stopped at a traffic light. The first time I noticed was in June, I felt it buck and the check engine light blinked for about 40 seconds. I took it to several places and no one could come up with a code. Last week the check engine light blinked again but only for a few seconds and the slight bucking, a friend suggested it might be a transmission problem so I took it to the shop and again, no code. This week it seems to be getting progressively worse. When I start it in the morning it idles high then drops low, and sometimes stalls, stalled a few times as I was pulling to a stop. I took it to the shop again and the only code we got was P1812 - see manual. I looked this up online and read "P1812 Transmission 4-wheel drive mode selector circuit failure." I don't use the 4-wheel in it, but can this be the cause of my bucking and rough idle problem? I'm taking it back to the shop in the morning and I would like to be somewhat informed on what this means.