My Rav4 has averaged nearly 24 mpg since I bought it in 2009. Last fall, when it had about 81,000 miles on it, we took it to the dealership for a ‘tune up’ in which they changed spark plugs, etc… Since then the mpg has plummeted to just over 18 mpg! We took it back several times & they can’t get the mpg back to what it was originally. They said they put iridium plugs in it, which was what it had originally. They also cleaned air filters, etc. We’ve called other dealerships & Toyota headquarters but no one can tell us why the mpg plummeted. The car no longer has the zip it once had; it’s rather sluggish on take off. Can anyone give us a clue as to what’s happening? Thank you for your attention.
They put Iridium plugs in, but I’m wondering if they used cheap off-brand Iridium plugs instead…cars today don’t generally like non OEM spark plugs. You could take it to your local independent mechanic (I wouldn’t personally go to the dealer for a 2007 vehicle) and have them put in the original OEM plugs (check your owners manual for which brand that is, I think it’s either Bosch or NGK).
2 other thoughts I had, if they changed tires at the same time and you went from a set that has a lower rolling resistance to a set with better traction, that will affect your MPGs (of course make sure your tires are properly inflated as that too will affect your mileage). Also, this extremely cold winter combined with winter blend gasoline (which already lowers MPG on it’s own) has definitely had an adverse affect on my gas mileage and this could be factoring in for you too
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Does the engine heat up quickly to operating temps?? If the thermostat failed, mpg’s would drop and stay down even with warming temperatures. If the shop changed the T-stat and you got a bad one, or they installed it upside down, that would be the cause.
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Check to see if the tires are inflated to the recommended pressure. Check to see if the engine is warming up. Is the temperature gauge coming up into the normal heat range?
These are the simple things. In the old days, we would have figured that the timing was not set correctly. However, today’s cars have timing that is set by the computer. The timing, though could be affected by improperly gapped spark.plugs. I had a 1993 Oldsmobile and had it “tuned up” by a GM dealer and experienced a drop in mileage and performance. I took it back and got no satisfaction. I lived with it for a year and took it to an independent shop. It has been quite a while ago, but I know the spark plugs were replaced. The mileage went back up and the performance improved.
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As I think about my response above, I seem to remember that the spark plugs were different that the GM dealer installed than what was listed in the manual. The engine was the 3.8 liter and I had taken the Oldsmobile to the Pontiac dealer. The dealer swore up and down that the plugs he installed were the correct replacement spark plugs for the 3.8 liter engine. I think the independent shop replaced these plugs with what the manual specified. I would have changed the spark plugs myself, but the rear plugs were hard to get to.
I find it hard to believe that “the dealership” which is presumably the Toyota dealership, would install “cheap off-brand iridium plugs”
You would think the dealer of all places would use genuine Toyota parts, except perhaps for the motor oil, which is probably delivered in bulk by their supplier
I guess you could look at the receipt and determine if the plugs installed were the EXACT ones called for in the manual . . .
What about coasting when you take your foot off the gas- have you noticed it doesn’t coast as well as it used to? This could point to dragging/sticking brakes. Just something else to consider as a possible cause…
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One other thing:. Is the transmission shifting into all gears? For instance, if the automatic is a five speed, is it shifting into that 5th gear, or is it staying in 4th gear?
That would definitely be a logical thought, but about 10 years back, there was a Honda dealership in NJ that was removing OEM spark plugs, batteries, and tires from new cars, and substituting cheap-o aftermarket parts from the Pep Boys store across the highway. Then, they would sell the purloined parts over the counter at their parts department. To Honda’s credit, they eventually revoked this crook’s franchise–although it took them several years to do so.
While that type of larcenous behavior is rare, it certainly isn’t unheard-of.