So I decided I would reach out for some help here. I have a 2010 Prius with 170k miles. A couple of months ago I started to notice that the car would sputter a bit during a normal acceleration and in between 25 and 30 mph the engine would start to do the death rattle like it was misfiring. So I started with some normal maintenance stuff like, new plugs, new coil packs, new fuel injectors, cleaned the throttle body and the throttle body sensor. Non of that helped at all. After doing some work on the car I accidentally left the mass air flow sensor disconnected and the car ran great (besides poor gas mileage). I though I had the problem figured out with a faulty mass air flow sensor. So I just replaced the mass air flow sensor and plugged it in and the car still runs like garbage. Unplug the air flow sensor, car runs great. Any ideas would be super helpful
The simplest way to see where you're at, is to check the degree of carbon build up in the EGR pipe, a stainless steel connecting pipe between the EGR valve and intake manifold. Watch @NutzAboutBolts video #16 here: Nutz About Bolts Prius Maintenance Videos | PriusChat Two or three other videos linked there too, for the full cleaning of the intake manifold, full EGR clean, and Oil Catch Can install. Good thread: EGR & Intake Manifold Clean Results | PriusChat Another: Oil Catch Can, Eliminate that knock! | PriusChat Somewhat tools worth having: E8 Torx socket (mandatory) E6 Torx socket (optional, but good to have, to remove the throttle body studs from intake manifold) 3/8" ratchet wrench, regular and long handle, flex head, you can never have enough 1/4" ratchet wrench, or 3/8" to 1/4" reducer Ratchet extensions: you can never have enough Long needle nose piers, straight and bent tip Ratcheting 12mm box wrench (optional, but makes disconnection of the EGR cooler from exhaust easier) Torque wrench (3/8" and 1/4" both good to have) Floor jack and safety stands (or ramps): basically some method to raise front, if you need to take underpanel off, which you may need to, both for access and to recover dropped items.
Well last night I took my intake manifold, throttle body, EGR, and EGR cooler off. Cleaned everything and the carbon on the inside of the EGR was unreal. I cleaned it all off with throttle body cleaner and brake parts cleaner. The EGR cooler was completely caked. It took 3 cans of parts cleaner and a pressure washer but my EGR is finally clean. I got everything reinstalled and it helped out a bunch but unfortunately, my problem is still mildly there and my gas mileage is staying around 37 mpg. Would the EGR valve cause this? Is there a way to test it?
You said you unplugged the MAF sensor and everything ran great? Have you considered changing the MAF sensor since I didn't see you mentioning a bit about changing that part? Edit: I just noticed you mentioned a bit about that part. If you said that when you disconnected the sensor it ran great and you changed the sensor and everything was bad again, have you considered checking the harness? It might be the harness that has something wrong since we might be able to be certain that it has something to do with the sensor. Since the sensor is brand new and the problem is still there, might as well check the harness.
More likely what's happening is that without the MAF sensor the engine only runs in "open loop" mode. And the OP's problem is only occuring with "closed loop" mode. In open loop (used when the Prius is warming up), the air/fuel ratio isn't monitored, and the PCM uses some default guesses for how much fuel to mix in. Once the coolant and air/fuel ratio sensor are warmed up, the PCM uses the air/fuel sensor as feedback to precisely control the ratio. (In order to know how much fuel to mix with the air, it needs to know how much air, and hence MAF is required.) One of the things that happens in closed loop is the use of EGR, and in practice it tends to kick in right around 25mph. (It's dependent on engine load, not the vehicle speed.) That's not a slam dunk diagnosis, but at OP's mileage there's zero doubt EGR cleaning was necessary anyway.
I don't know if you're still having this issue or not, however, I just had the same issue with my 2013 Prius and there appears to be a small 2 hose valve behind the Air Filter box and mine was, some how, disconnected. I plugged my hose back up and added small hose clamps to prevent another "episode", as it were and my car runs like a champ. The hose in question, for me, looked to be a vacuum hose that ran to the throttle body and it was pulling in un-metered air which caused us to run too lean and was running like pure shit.
