When you touched the accelarator, usually the HPCA (housing pressure cold advance) / Fast Idle solenoid kicks in. This aids in cold start up and will normally kick the rpm's up some 500 or so until a sensor in the block says it is warmed up enough. As Dmax said, maybe a sticky throttle cable or some other wierd situation caused it to jump up even more. Then maybe, I'm guessing, it was a coincedence in timing that when you put it in gear, the sensor gave the "warmed up" signal to the solenoid and kicked the fast idle off.
Does it do the same when it's whened up?
Has it done it before when cold? Maybe it was colder this morning..
See if it does it tomorrow morning or next time when it's cold. The fast idle can be set as soon as the ignition key is turned on and the glow plugs are firing.
I actually have a switch to bypass the fast idle just so it won't run high for any longer than I want it to, which is usally after 10 seconds or so.
Mark Chapman DP member #653;
1983 K2500 6.2 Suburban, 4" lift, 35" tires, ATS turbo, Banks exhaust/intake, pyrometer, tachometer;
1986 K5 6.2 Blazer, 2" lift, 33" tires, Banks intake, pyrometer, tachometer
1963 wife, one owner, average mileage for the age but in excellent shape, a keeper
1992 daughter, low mileage, pretty, limited edition, but requires some money to maintain
1995 son, sports model, very fast & peppy, time will tell on durability and maintenance costs
"Grease is good"