I have a 2004 Prius with 230 K miles. The car shows the following symptoms: * Rough idle especially when cold * P0171 code and triangle of death one time * Gas mileage is off. 40mpg on highway instead of 50. 29 in city. * Engine will rev high without correct torque. * Engine is louder than normal. What I have done: * Replaced upstream O2 sensor * Replaced MAF sensor. * Replaced the spark plugs and air filter. Although these improved performance they have not fixed the problem. I still get the P0171 code and the check engine light on. The engine still performs weak compared to what it used to be, although it does run better when warmed up but the mileage is always off. Is the next step to check the fuel pressure? How do I know if the fuel injectors are good? Thanks for any advice! Ken
Have you checked and cleaned the throttle body and related components, as the PCV valve? To me, this seem likely culprit based on your description. When you do, afterwards disconnect negative battery terminal - to make the ECU re-learn throttle body opening/percentage… and those vital radio stations and clock….
I will clean the PCV valve and reset the computer and see what that does although I have read that others replace the PCV valve and didn't see any change. I will post back results. Is there a way to check the fuel pressure with a handheld scanner instead of having to do it physically? I can't believe they put in a tank with a permanently installed fuel pump. WTH
Priority is to clean the TB. The PCV is a basic one way vent.. it’s less likely the issue. Your throttle body plate is probably full of deposits - it’s a very common G2 issue. Clean it good with propanol (or buy wasteful special cleaners). Check car care nut video linked;
I was going to replace the PVC valve and was shocked to see a hole next to it on the valve cover. I suppose I'm going to have to replace the valve cover now and gasket of course. (See photo) I don't see how this could have happened.
With this engine, it's so easy to make a hole there that Mendel drew up a nice sketch back in 2018: Advisable to use a socket there if possible, not an open-end wrench.
When I had all the same symptoms I replaced all sorts. In the end, it turned out to be the cat - although it didn't throw a code. I put a spacer on the 02 sensor and it ran beautifully after that
