high idle engine surges code p0420 ????

This has been going on a long time first the high idle about a year ago I replaced the IAC valve and cleaned the throttle body and the problem remained. A few months later the idle seemed to go back to normal for about a month than the idle went high again this time the engine would surge when driving at a steady speeds on random occasions then the check engine light came on and I did not check the code before it went out and the surging stopped. However the idle remained high. Now idle is high surging is back and check engine light is on with a p0420 catylist effenciacy below threshold (bank 1). I have almost 300,000 miles and don't want to invest a lot of money but the truck runs great and i have not had any drivability problems since I bought it 150,000 miles ago. What should I do? This is a 2.7 L 4 cil.

 

have you checked ECT sensor. On older Toyotas ECT is what sets idle.

 

A truck with that many miles is bound to have lots of soot buildup in the cats and manifolds. IMO I would seafoam the intake by suction through one of the vacuum lines. There is no guarantee it will solve all your problems but it's worth a shot. It will throw a few codes right after seafoaming it but those usually clear after driving it hard 30-40 miles. There are a few videos online showing how to seafoam a Tacoma. Good luck man.

 

Just got my truck out of the shop $350 for them to diagnose that it needs a throttle body. They spent 4 days trying to figure out why the idle was high. A new one costs about $1000 so I'm opting for a used one and the shop I took it will not buy used parts so I'm doing it myself. Used one about $150 not tough to change thanks for your advice but this was a tough one to diagnose.