I recently purchassed a 92 Buick Park ave Ultra. Great car with 175k.

The care runs very well on the road however at stop lights or just ideling, it runs very rough. Once i step on the gas it's a smooth take off and back to
riding on glass.

Can anyone help with a diagnosis or starting place for this rough idle?

Thanks in advance

Welcome to AF.

Start with the basics like checking the condition of the plugs, wires and PCV. Since you just bought the car, it may be just in need of a tune up. If it is, don't forget a fuel filter too.