So I recently bought a 1990 Toyota 4x4 ext cab. its got the 3.0L in it and some times when i start it up the idol will jump up and down... but when i drive it it stops... or sometimes while driving when i push in the clutch or put it in neutral it starts to do it again but not all the time.. does it sound like a vacuum leak or something to do with my fuel system

 

Sounds like your idle is set too high. Bring down the idle a little bit and see if it helps.

 

Is your coolant full and at the proper anti-freeze/water ratio?

 

I have found there are a fe things that can cause the "surging" idle.

1) low coolant
2) vacuum leaks
3) tps out of adjustment
4) IAC valve gummed up/not working
5) afm out of spec
6) low compression

and so on.... start checking things out.