1997 TRANSPORT Surging

[tobas]

Wondering if I have a vaccum leak causing the van to surge at idle (can be felt & heard but does not affect RPM).
Where do vacuum leaks typically occur for this year and how do I find them?
The van is not leaking internally or externally any coolant (dexcool). Vehicle runs warm not excessively hot and reads around the 12 o'clock or lower range on temp gauge. Fans will come on if it runs anything above this temp or if engaged by a/c. Oil is fine no milky contaminents. No white smoke present from the exhaust.
I would hesitate to think it is an intake manifold gasket or head gasket leak but I'm not entirely sure??
If not a vacuum leak, what else could cause surge (no codes)? Faulty or dirty injectors? TPS sensor?

*surge also can be eliminated by engaging a/c
Any help would be appreciated!