94' Pickup. Problem under the hood

Hey there,

I am not very tech savvy so I will try to explain this as best I can.

I took my truck into the shop, twice, for inconsistent idle. This problem would happen when at a stop sign, or slowdown in traffic, the idle would go high then low, high then low etc etc. The guy at the shop reset the idle, and cleaned some throttle pump? Anyway, it seemed to fix it, for a while

Now though..when I am at a complete stop..my front end of the truck shakes, every 1-2 seconds, like side to side. It ONLY happens when my foot is on the brake. For instance if I am in neutral with no foot on brake it doesnt happen. When I am in neutral with foot on clutch but NOT the brake, it doesnt happen. Only when I have my foot on the brake, it shakes, and at times somewhat violently

Any idea what this may be?

Thanks

What kind of truck, 2wd or 4wd ?

What engine 4 cy or 6 cyl ?

Oh yeah, auto or manual tranny ?