My wife tells me the other day that the engine in the Catera was shaking as she was driving home the night before. I went out and drove it about 10 miles and no problem. The check engine light was on for a few days before, but it would often go out, and then a few days later come on again. I noticed that day that the engine seemed to be running ok and the check engine light actually went out while I was driving it. I had had some leaking radiator fluid drops on the garage floor for a month or two and had the dealer check it out and he said it would cost a whole lot of money to fix the minor leak as it meant taking the engine apart to fix the oil cooler gasket or something. Anyhow I just added more coolant every three weeks or so and tried some of the stop leak stuff that looks like liquid silver filings. No difference. Then a mechanic told me that cadillac recommended some little brown pellets, so I added those and bingo, no more leak. So I'm driving away from the convenience store stop (that same morning) and the check engine light came on again and when I came to a stop light, yes, the engine started shaking. So how sick is this baby. It almost seems like its missing and is very sensitive to any acceleration, it shakes more then. Any thoughts will do.