Prius III engine knocking at high torque low RPM (solved)

No. Something else.

EGR is rarely used at idle. If you have problems at idle, something else is going on.

Bob Wilson

 

Wouldn't that be more consistent with the EGR valve leaking or failing to close? That happened to my Mazda, causing symptoms similar to those of a vacuum leak---which it was, except that exhaust instead of air was leaking into the intake.

 

Hmm, OK but I read this statement: An EGR valve can stick open when it should not, causing a rough idle or hesitation.
Can this stuff be properly tested with the diag software?

 

It may be if we check the long-term fuel trim. Speculation, you've ask a good question.

Bob Wilson

 

yes, TIS will show you flow rates in real time.

 

I might let the shop take car of the diagnostics. I have to stop screwing with it at some point and get it out of my head
If you want to hear and see what my cold start idle is like:

 

it's certainly sick. if P0401 is the only code, fix it per the TSB and see what happens.
P0410 is for secondary air injection. your prius doesn't have one of those.

 

An easy thing to do to see if the EGR valve stuck open is causing your idle problems would be to just block off the EGR pipe. Use a piece cut from an aluminum can and block off the pipe where it connects to the valve.

 

That was exactly my thinking. But it's a complex system with all the sensors and things. Have to see if I want to keep tinkering but will keep you posted once I find a solution.

Just read this P0401 diagnostics page from Toyota
P0401 Diagnostic Code - Trouble Code Diagnosis Guide

This part was interesting to me :"When a P0401 code is tripped, it is because the DPFE sensor found too little recirculation."

Let's say the DPFE sensor is faulty and signals there is not enough flow, the valve would be constantly full open. I would think this would make for a rough idle too? What would happen if I just unplug the sensor or unplug the plug by the EGR (EGR is electric not vacuum)? Don't want to trigger other codes nor damage the computer.

 

Hmmm, I know where the MAP sensor is, but where is the DPFE sensor? And how do you test it? My car has the pinging, but has not thrown a code.....yet.

 

Good news. My Prius runs as it should again.

I had to look around to find a somewhat local mechanic that is able to tackle the Prius. Found Essex County Auto Repair in Middleton, MA 01949. Kyle the owner was very helpful even though I went there the first time ever. I explained to him what work I had done so far and mentioned the nice folks at priuschat with the various tips. He agreed that after what I've done we should look at the proper function of the EGR. He hooked up his Snap-on scan tool (wanted to avoid the Toyota software fee). We put the car in maintenance mode and he manipulated the valve to fully open and close. A little bit of a difference in how it idled was noticeable but noting made it run as it should. Kyle felt he would need it in the show for further looking into it and make sure the EGR is the problem. We agreed that I would install a temporary block shield to further narrow it down and then call him up to make an appointment. OK, so code reset car turned off shook hands and off I went. On my drive home I was already thinking that the car runs awfully smooth. But I wrote it off to imagination as I was already pleased to have a path to solution in sight. Later that night I had to take the Prius out for anther ride..... NO MORE ISSUE! Wow, what happened? My only explanation is that manipulating that EGR valve must have made it unstuck after all. Day 3 and all is still well. Contacted Kyle and we are going to wait and see if the issue is coming back. I would say that probably the EGR was stuck open as suspected.

 

Great news!! It's not very difficult to replace the EGR valve. There's a video in the Sticky part of this Forum which shows how.

 

That's the PCV valve I think? EGR is a bear, hooked up to four coolant hoses, way at the back.

 

oh. How embarrassing.
If it's ok with you, I'll shut up now...

 

I just love to be the bearer of dour tidings.

 

What? Are we confusing the EGR valve with the EGR cooler (heat exchanger) to which it is attached? The valve, or what I thought was the valve, looks relatively easy to replace. The PCV valve, unrelated, is buried deeper than on any other car I've met.

 

Numbers 3, 4 and 7 above: number seven the most clog prone, and of course hardest to access.

 

I also thought that #3 was EGR valve, and #7 was EGR Cooler. (And that #7 is the most clog prone and hardest to access, with coolant tubes, as you correctly note).

 

Just a little update. My Prius is still running smoothly. No more stuck valve. No idea how it got stuck only once. But hey, I am happy for now. Got my great MPG back too. Keep on running....