I think we should rewind a bit, the motor mount issue was to fix what the dealer assessed the first time around as a symptom and their "fix". What was the reason you took it in for service at 30,000 miles in the first place? If it was vibration or miss or fuel starvation, the additional stiffness of the new mounts would only exacerbate the symptom, not relieve the cause.
You could have had poor fueling (fuel tank filter clogged, fuel pump or hoses in the tank) or simply picked up bad gas that started the whole sequence in the first place. You could also have ignition problems or electronic sensor problems as early EFI system was probably fraght with pitfals as well. Sometimes it is just best to take a deep breath and stop going down a merry path of diagnostics that you were led down. When troubleshooting, simplifying and divide and conquer troubleshooting makes more sense than throwing hardware in with back and forth trips to the servicer.
You could have had poor fueling (fuel tank filter clogged, fuel pump or hoses in the tank) or simply picked up bad gas that started the whole sequence in the first place. You could also have ignition problems or electronic sensor problems as early EFI system was probably fraght with pitfals as well. Sometimes it is just best to take a deep breath and stop going down a merry path of diagnostics that you were led down. When troubleshooting, simplifying and divide and conquer troubleshooting makes more sense than throwing hardware in with back and forth trips to the servicer.