Trouble with EGR and Mass air flow 2011 Prius

You should take apart the intake manifold and see if that's plugged up with carbon as well. Hopefully you are not at the "bad head gasket" level yet.

 

How many miles?

 

Cleaning time. Some info in my signature “bad flywheel” (on a phone you may need to click my avatar).

 

There are a lot of potential causes of misfires, and finding them can be subtle, especially when they occur only in certain driving conditions.

There was a pretty good article on misfire diagnosis in the Second Quarter 2009 issue of Toyota Tech, starting on page 15.

 

Leak-down test is the go-to for head gasket failure. Maybe you’ve dodged it, but still good to verify.

 

It may not be a minor issue.
Were the plugs replaced at 120,000?
Exchange components between cylinder 1 and 4 and see if the misfire follows.
As mentioned above.....leak down test.

 

Humble opinion, based on longtime observation: this is the point in the typical misfire diagnosis where I think it's almost always worth first trying to eliminate the EGR valve (and EGR passages in intake manifold) before checking the headgasket. Because a) it's a known suspect and, b) it's easier/cheaper/more-DIY-able to check.

(This is for cases where the misfire mainly happens during likely EGR operation -- i.e. when the engine has warmed up enough to enter closed loop, and is under some load but not wide open throttle. That's when the valve and especially the intake manifold are suspect. )

But yes definitely warn about possible HG failure because leaving that unfixed could lead to catastrophic damage. Start keeping an eye on coolant while checking the easy stuff, that's a no-brainer. Put the HG top of mind, but not top of list is what I'm suggesting. Hope that makes sense.

And of course since other misfire suspects are still in play, swapping coils e.g. is a worthwhile test.

 

The OP already did the ERG rinse and set.

 

I got that, thanks. I should have emphasized the phrase *typical misfire diagnosis* because I'm trying to get PC (mostly Mendel ) to modify the misfire diagnosis flow chart.

 

For the typical headgasket failure on this car you won't notice anything in the oil or coolant. Instead coolant begins slowly leaking into a cylinder and gets blown out the exhaust. As the leak gets larger, you might notice rougher cold starts. Anyone suspecting this kind of leak should go out in the morning when the car is cold and mark the level in the coolant reservoir with a grease pencil (or whatever). And then check it every morning. (While continuing to look at other possibilities.) If you notice coolant loss over time with rough cold starts, you could pull spark plugs and look for coolant pooled in the cylinders (it will probably be in only one). A $20 USB endoscope helps since the plug tubes are so long.

Since you know you've got misfiring that is possibly due to the EGR because it happens mostly when the engine is warmed up (and running in closed loop), you can test for it a little more directly than unplugging the MAF (which does also take it out of closed loop and cuts out the EGR, but also takes out the use of O2 sensors and fuel trims). One way is to unplug the EGR valve connector (which will throw a code and turn on the check engine light). If misfiring goes away when you disconnect the EGR valve and comes back when you plug it back in, it's a really good bet the EGR valve itself is problematic or the intake manifold EGR ports are clogged unevenly.

FWIW a Toyota Master Diagnostic Technician recently posted a youtube video showing a misfire diagnosis technique that uses a putty knife to shim off the EGR valve flow. It looks pretty easy and has the advantage of not telling the computer that your EGR valve is unplugged. (The ECM will tweak its behavior somewhat when it knows the EGR valve is unplugged.) A shim also has an advantage in a case where the valve is suspected of being stuck open (rough idle).

If you try either of those, let us know how it goes.