Jim Grant's Tech Tips

90 Toyota Celica 2.2l DOHC, Rough Idle Problem
Q: This ‘90 Toyota Celica 2.2 liter with DOHC came to me with a very unstable idle. When I pull forward and hit the brakes the idle will bounce from 300 to 1200RPM continuously. The car has heavy exhaust fumes that will burn your nose and eyes! There are also multiple skips at idle, but the car runs good on the highway. The 02 sensor shows a lean problem. There are no codes in the ECM, the fuel pressure is good, vacuum is low (15hg.) no vacuum leak found. The car runs better with the return fuel line pinched. If I pull the EGR full open, the car will just idle higher but not change in running pattern. I have tested all of the major sensors, checked for interference from the alternator. Where should I go from here? I have been working on cars for 15 years plus, but this one tells me everything I learned is wrong.

A: I would suggest a close inspection of the valve timing/timing belt. It sounds as if the timing belt may have jumped a tooth or 2 causing one or both of the camshafts to lose timing. The low engine vacuum is also another indicator of valve timing problems. The vehicle’s computer will do one heck of a job at hiding that type of condition, sending a tech chasing his/her tail. Been there, done that.