I am having the EXACT same problem with my 94 SC400, 84,000 miles, still running fine.
My mechanic says that his diagnostics show the car thinks everything is just great. He cannot locate any problem whatsoever and is at a loss to even suggest what it might be.
Other than the "misfire", everything is wonderful. My symptoms are just a bit less demonstrative than yours:
--The idle speed is within spec. approx. 700 rpms in park and 583 in gear. (SAME FOR ME)
--Tachometer is not getting the proper tach. signal. (DON'T HAVE THIS ISSUE)
--Have a random misfire. (ONLY IN IDLE, EITHER IN PARK OR AT A STANDSTILL)
--Car shakes slightly after it warms up when the idle comes down to 700 rpms. (DON'T HAVE THIS.)
--Engine mounts have never been replaced. (SAME FOR MINE)
Would love to hear more about this....it is driving me crazy! Thanks for the great summation.
AJ
ajwms@hotmail.com
