Find a mechanic with a scanner, or you might be able to borrow or rent one from an auto parts store. View "live data" while the engine is running. In particular, you want to look at the "AIS steps". That is how many steps the automatic idle speed motor is opened to out of 256. A typical value at idle is 32. If it is higher, that suggests something is causing the engine to slow down and the computer is responding by turning the AIS motor to increase speed. That could be caused by simply putting it in gear.
You can expect to find one of two things. If the number of steps is very high, say 50 - 100, the Engine Computer is trying to raise idle speed in response to some incorrect condition, typically a sensor value. If you find the steps closer to zero, the computer sees that the engine is running too fast and it is trying to bring the speed down. That would be typical of a vacuum leak.
Try spraying water when the engine is still cold, and watch for places it gets sucked in and the engine slows down at the same time. Spray around the base of the throttle body and the bushings for the throttle shaft. Pinch off the large vacuum hose going to the brake power booster. To be running that fast, you will be looking for a pretty good-sized vacuum leak, not just one of the little black hard plastic hoses. If you have cruise control, see if it works. If it can't hold a steady speed, that too suggests a vacuum leak. If it doesn't work at all, check the vacuum hose going to the servo. It should be near the battery. You can also follow the throttle cable to the servo to find it.
Friday, December 3rd, 2010 AT 4:27 PM