2002 Prius Rough Idle

1. Clean the throttle body interior and throttle plate. Remove the air cleaner housing, spray some throttle body cleaner on a clean cloth, and scrub off the dirt in the throttle body and throttle plate with the cloth.

2. Replace the iridium spark plugs using the correct NGK or Denso plugs as specified in the owner's manual.

 

Yes, the fuel injectors would be the next logical area to investigate. You can try Chevron Techron or an additive of your choice first; then if that doesn't work, remove the injectors and clean or replace them. Don't forget to replace the sealing O-rings as well.

 

We did a test here about a year ago with another member's injectors who was having a rough-running problem. He first tried injector cleaner in the fuel tank, and still had the problem, so he replaced the injectors and the problem was solved. Instead of tossing the old ones, he sent them to an injector servicing facility in Michigan and I paid for them to be reconditioned, with a flow and pattern test before (they sucked) and after (excellent). See this post for the test results.

The test strongly suggests that the fuel tank additive products don't do much, but the off-car reconditioning restores them to excellent performance. There's a write-up at importtuner.com of a similar test with the same conclusion.

I still have that reconditioned set, make an offer if you're interested. With a good set on hand, you could just replace them in one go and have the car on the road, without any downtime from sending the old ones for reconditioning and waiting to get them back. Then if you wanted to, you could get the old ones reconditioned as a spare set, or pass them along to another member.

-Chap

edit: By the way, I've read (but not confirmed for myself) that you may be able to identify dirty injectors with a good auto stethoscope: listen for the sharp metallic tinktinktinktinktink of a clean one versus thupthupthupthupthup of a dirty one while the engine is running.