Toyota - Corolla :: Shuddering / Pulsating When Stopped At A Red Light

A few weeks ago on a short drive, my car (2000 Toyota Corolla) started shuddering/pulsating when I was stopped at a red light (and it kept doing that intermittently as I drove the few blocks home.) Next time I tried to start it, it turned over but then died. Towed it to the mechanic, he said it was a dead ignition coil, he replaced the coil and it was able to start again.

Less than a week (and not much driving - 50 miles tops) later, on the highway, it starts shuddering again, feels way underpowered, and the check engine flashes. It's pretty scary. I pull over and have it towed to the mechanic. (It still starts up but doesn't feel safe to drive, plus the check engine light is flashing.) First he says one of the fuel injectors needs to be replaced, then he says that on further testing it was actually another dead ignition coil. He replaces the ignition coil (he didn't end up replacing the fuel injector) and I pick up the car.

It's fine on the drive home (which is about 3 city miles, no highway driving) and on another neighborhood errand, and the check engine light isn't on, but now it's sort of shuddering again. I don't want to keep driving it and/or try it on the highway to wait for it to get worse.

I guess I'll take it in again tomorrow, but does this seem odd at all? I know some people replace all 4 ignition coils at once pre-emptively, but it would seem strange for 3 to fail within ~150 miles (assuming this is yet another ignition coil.) What else might be going on? I had the spark plugs changed last year so those should be fine. The car has pretty low miles on it (about 100k) for the age.