37mpg average 250K miles, batteries and trans 100K miles

1. What does the engine air filter look like?
2. What is the engine oil consumption rate?
3. Have you had engine compression readings taken? If not, this would be a good time to do so, to assess the basic health of the engine. Toyota Techstream is needed to spin the engine at an appropriate rate (if you do not use software control over the hybrid vehicle ECU for this test, MG1 will spin the engine too quickly to have good compression test results.)
4. Even if the engine compression is OK, if the engine oil consumption rate is high, the catalytic converter may be plugged up so that the engine cannot breathe adequately, which would reduce engine power output.

 

How the tires wearing?

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Is there any way too know the cat is going bad besides cutting off to see if symptoms go away or simply replacing? That is a difficult call to make if your engine may be on the way out.

SM-G920V ?

 

Vvt solenoid valve left side of engine right by the manifold
OEM Part Number:15330-21011

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'i'm trying to figure out why'

'the engine is on the way out'

'i'm about to take a trip'

 

Typically a severely plugged cat will result in poor engine power. Also likely to get a P0420 code.

When you say it's struggling, do you mean struggling due to lack of power or just struggling to get decent mpg?

What are your wife's recent driving habits? Has she changed her normal driving distances? Does she do only 5-10 minute trips? This easily results in mpg in your range.