This should be an interesting one. This problem started a few years back and doesent hinder the driving ability after the car is warmed up, so I still drive it everyday and go though the same thing. When the car is first started, it idles around 1500, then shortly after, drops to under 500 and runs really rough and rich with black smoke out the tailpipe of course, but never stalls. After a few minutes, the fast idle must be kicking in and will literaly pull you down the road, UNLESS (heres the weird part) I push on the clutch even the slightest bit, then the idle drops back to around normal. This is the weirdest thing ive ever seen and wonder how the throttle on a carburated model could be somehow affected by the position of the clutch. After a few more minutes, the idle is taking off on its own again and it will not come down, even by pushing the clutch in,and it usually rides up around 3000 or a bit higher, which has really been worrying me, being it has about 150,000 miles on it. Only after about 10 minutes of running/driving, does the idle come down and continues to run perfectly for the rest of the drive. If its a colder day, and I restart the car, the idle immediatly shoots up to 3500 and will not come down untill a few mintues pass. If I shut the engine off in the midst of this high idle, it will diesel (like pre-ignition) until I push the gas to the floor to flood it out. I do have a bearing in the gearbox that is growling, I think its the main input shaft bearing, when the clutch is pushed in the noise stops, and growls in every gear, and in neutral with the pedal out. Any help or info would be greatly appreciated.