97 Avalon occasional misfire

I have a 1997 Avalon run for 113,300 miles, until today.

2 months back it gave the following problem.

While on running, the car will show jerks, RPM meter hand will show little waver, exhaust will sound like dhoop dhoop dhoop…

But no Engine Check/any lights on the dash board during this problem time.

I switched off the engine and left it like that for one hour. Started again, car was running & driving fine.

Later I used the Chevron’s Fuel line cleaner liquid mix with Gas also.

Again couple of days back I got the same exact problem. Misfires - Exhaust Dhoop, Dhoop… & RPM meter hand wavering - No engine Check Lights / Any.

Stopped the engine & left it like that until next day. Now, it is running & driving normal, again.

But as it has appeared second time, it is likely to show up again, anytime.

Any help on this occasional Misfires(?) on my '97 Avalon is appreciated. Thanks a lot, in advance.

Other Details on my car.

-Timing Belt Changed at 62k miles

-Spark plugs last changed date, No Idea

-Battery changed a year back

-Air Filter is decently clean & replaced at 92k miles

-90k miles service suggested by Toyota done at 92k miles by me

-During this 90k service nothing was reported on this like spark changes, etc.

You are way overdue for new plugs. And if this is a distrbutor based ignition system, wires rotor and cap also.

Start there. And check for any stored codes, even though the light isn’t on.

From that step I might proceed to cleaning the EGR valve, as they can get messed up with carbon and start sticking, giving an intermittant poor idle.