Trouble Persists After EGR, Cooler Replacement

Did you clean the EGR ports in the intake manifold?

 

Just a thought: could a dirty MAP sensor be the cause? With all the oil that gets by the PCV valve, this sensor gets its share, and might be giving the engine control module a false reading.

 

Yeah. The EGR passage runs right through, splits into 4, they come come out, one per intake port. Watch @NutzAboutBolts videos.

 

He has a youtube channel, and the Prius ones are linked here:

Nutz About Bolts Prius Maintenance Videos | PriusChat

 

At each "port" on the intake manifold it's the small opening, 1/4" diameter.

I found a brush designed for cleaning stainless steel drinking straws worked well. Start it in, then add a little shot of brake cleaner, work it.

 

So, how did this turn out?

 

I've got the same problem. misfiring on mild acceleration only - Idle and top end runs perfect. Remove the EGR plug from the valve, and the engine runs fine. I've cleaned the EGR cooler, the valve, the pipe, and the intake manifold - including all the 4 small ports. No change, but there was hardly anything there anyways. I've checked the EGR wiring back to the ECM - all good. Same with the MAF wiring. No engine codes either, unless the EGR plug is disconnected. I've checked the plugs - all in excellent shape. I thought about the fuel pressure, the injectors, the coils, and the PCV valve. Not checked these as yet, but all these items (and plugs too) should affect the entire range of engine operation, so not considering these likely culprits of the problem. I'll do a MAF and MAP sensor clean, and see if that helps. The oil catch can is also perhaps something to consider. Will post again if I find out what this problem is.

 

Maybe you got a bad EGR valve. Is Rockauto reliable with respect to counterfeit parts?

 

A couple checks you can do are:

• Retrieve the car's most recent EGR flow test result (naturally, reconnect the valve first, and make sure you're looking at a test result from after you did that)
• Perform an active test where you control EGR step position (as you can find described in the troubleshooting steps for P0300)

If your misfiring is EGR-related and if it does come and go according to when the ECM wants EGR applied, then the good news is, that tends to rule out an EGR valve problem. The valve must be opening and closing at those times if it is causing the misfiring to come and go.

Even after you've said the manifold EGR passages and four small ports were cleaned, those are still the likeliest suspects for misfiring with that particular pattern. Might be worth a careful second look. But it also won't hurt to get some actual data from the two checks above.

 

OK, I've not had much chance to investigate much further, but I did find out some new clues. First, the condition worsens with engine temperature. This threw me for a loop. Its really VERY minor when the engine is cold. That caused me to incorrectly describe the condition. I thought the problem went away when the EGR valve was electrically disconnected, but this is not the case. I had a chance to try this while the engine was warm today, and there was hardly any change in the problem. I thought possibly the problem got worse actually. So, I'm starting to suspect a bad valve. Even though I've measured all the coil resistances in the valve motor, and it seems to be able to turn freely, AND I've replaced it with a used one. If there was a bad valve I would have thought the computer would detect it, but I guess its possible its under open loop control. Will update again with more news when I find out.