Service Writer is right about the timing belt, but here is another related problem that can be impossible to find. There is a camshaft position sensor on the left side of the engine, and a crankshaft position sensor on the back of the block. When the timing belt jumps one tooth, the engine computer will detect it and turn on the "Check Engine" light. It will run as you described too. If the belt jumps two teeth, the computer will shut the engine down to prevent valve damage as Service Writer explained. Three teeth off and valves will hit the pistons.
If my story is right, and the problem gets worse, your Check Engine light should be coming on pretty soon and you will have a diagnostic fault code memorized in the engine computer for "Cam and crank out of sync". In other words, the timing belt jumped a tooth. When you go to replace the belt, if you have the presence of mind to inspect the timing marks first, you will find the belt has NOT jumped a tooth, so you'll be scratching your head. If you don't bother checking the timing before you start the project, you'll just throw a new belt on and put it all together only to find it runs, (or doesn't run), just like before.
The problem, which is pretty common, is a sheared off locating dowel pin for the cam gear. The gear shifts on the cam just a little. Even though the cam and crank sprockets are timed perfectly, the camshaft is late. If the cam sensor were reading the cam sprocket, no problem would be detected, but since the sensor is on the other end of the camshaft, its pulses arrive at the engine computer slightly behind the crankshaft sensor pulses. This is how the computer detects the problem.
The fix is a new dowel pin. If you're careful, you can use wire to tie the belt to the sprocket so you won't have to go through the process of moving the belt around later.
On two of these I was involved with, I found I had spark on the two center cylinders, but not on the two outer cylinders. (One coil was firing, but not the second one). Also, there is a procedure for relearning the relationship between the two sensors, but I've never had to do that. Once repairs are completed, rotate the crankshaft two complete revolutions by hand to be sure no valves are hitting the pistons, then just fire it up.
Wednesday, December 2nd, 2009 AT 3:28 AM