Have you checked for stored trouble codes in the PCM? This should be your first troubleshooting step. How many miles does this car have? Many things can cause a rough idle. It’s quite common that rough idling is related to a dirty MAF and/or dirty throttle body. If you check on YouTube, there are plenty of videos on cleaning these items properly.
Could be.....intake manifolds on these cars are prone to breaking. You have any way to datalog? Tip offs for a vac leak are wacky short term fuel trims and long term fuel trims over a few % rich consistently. You can smoke check the engine to see if there is any leaks in the system. I made my own smoke checker out of a jar, an old soldering iron, a couple fittings and an old sock soaked in baby oil. Honestly, my datalogger shows classic signs of a vac leak but, I have never been able to find one and the motor runs like a kitty stuck with a hot fire poker. Another issue I've seen with these, especially the early cars is overfueling cold, the motor bangs the slug of fuel around until it pukes it out the exhaust port. Neither of these issues will set a code, in my experience. There are also the obvious things to check like spark plugs, making sure they are the right heat range and the condition is good.