Idle problem when? Cold engine or hot?
If it falters when cold the engine's "cold start system" isn't working
and needs to be repaired.
If the engine falters when it's hot a vacuum leak may be to blame.
Listen to it - for a hissing noise - perhaps from a broken or
disconnected vacuum hose. Such a leak will dilute the air / fuel ratio
and so cause poor idle but normal driving performance.
Dirty fuel injectors will benefit from an injector cleaner fuel
additive; it will improve their flow.
Suggest you find a more open minded mechanic!