Gas mileage reduction from 25mpg to 20 mpg

PIPPISMOM

MEMBER
2001 TOYOTA SIENNA
175,000 MILES

Until August 2013, my Sienna got 25mpg across all driving for the 7+ years ant 125,000 miles I have driven it. In August, I had a dealer replace the IAC motor, throttle body gasket, and idle speed valve assembly. The car now gets 20mpg across all driving -- 5mpg less, over the 3500 miles I have driven since then. The dealer says it must be due to weather conditions or driving changes, none of which apply of course. They are totally uninterested in helping the gas mileage problem, Any suggestions?

5 Replies

HMAC300

MECHANIC
48,601 POSTS

Scan for codes and check fuel pressure with a gauge first. Then check for a vacuum leak like a hose off, cracked or broken vacuum line etc.

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Monday, October 28th, 2013 AT 12:01 PM

THIS IS MIKE

MECHANIC
686 POSTS

Also check the air intake boot for a complete seal and make sure there are no leaks. Un-metered air could cause the computer to adjust the timing and amount of fuel that is being used causing poor mileage.

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Monday, October 28th, 2013 AT 2:47 PM

PIPPISMOM

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2 POSTS

Both suggestions sound worthwhile to investigate. Will do with my local mechanic and thanks very much. Any other suggestions also welcome! I appreciate you all's help!

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Tuesday, October 29th, 2013 AT 8:25 AM

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Too add, gas companies change their mixture to a less potent fuel because in lower temperatures pinging is a lesser problem. This sometimes effects mileage.

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Wednesday, November 6th, 2013 AT 8:33 AM

HMAC300

MECHANIC
48,601 POSTS

One other thing I forgot to add especially about this is if you use or can use fuels like E85 which means 85% alcohol and 15% gas then your mileage will suffer 25% if you use the 15% alcohol which is pretty prevalent out west in u.S your mileage will also suffer. So look at the pump when you start to gas up use only the 10% fuel mix.