Recently did a tune up on 97 Lc with 235k. New dist cap and rotor, factory Toyota plugs and air filter. At idle, in neutral or park, the idle has a periodic rough grumble for a sec or two, returns to smooth idle and keeps repeating. i checked for vacuum leaks and didn’t see anything, checked timing as well, @ 3 degrees. Any suggestions? Was thinking about wires and coil just for peace of mind, as I acquired this car recently and doing some deferred items. From the receipts it looks like the plug wires were replaced in 2008 but only 40k miles ago, no history on the coil. Wires were replaced with OEM, assuming the mechanic replaced them, as they are the factory original manufacturer. Any diagnostic tests I can do before buying parts?