I have a '96 T4R with over 250K miles. It's been maintained meticulously... countless oil changes, numberous sets of tires, one major engine tune-up and a couple timing belts. Currently, and not at all consistently, I get a vibration on ignition. Well, it's happened just 3 times, but enough to make me a little jittery. I asked a friend what he thought could cause something like that and he suggest timing. Do timing belts give warning signs or trouble coming, or are they silent until it's too late??? The current timing belt has a little over 100K on it. (I'm working on my 3rd one). Everything seems to be in good order ~ it drives perfectly considering the age and mileage. Anyone have any suggestions on what a couple seconds worth of shaking when starting might mean??

Yes, The belt can be visually inspected.....

Shaking only during engine cranking?

Worn timing belts do not give off any symptoms or warning signs. If you take the time to visually inspect it, you might as well replace it if you've taken the time to inspect it.

I have a 99 Tacoma with 174k miles on it and I'm getting ready to do my second one.

Use extreme caution when it comes to timing belts...you never know when it's going to break, and when it does you don't want it to break while getting on an interstate at 75 mph and see a tractor trailer on your butt.

There is also some mild vibration after 50 mph, up to about 70.

no warning, just pops

I do not believe the timing belt is the cause for shaking. If she shakes when idling only then it is usually the engine mounts.