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Gas mileage plumits

During Christmas vacation the gas mileage dropped from about 21 to 12mpg. Truck in not in 4wd, runs smoothly with no engine missing. Local dealer says it is A-F sensor, coil, plugs, pcv valve, Em sensor & fuel sensor. He wants $1875 to fix. Seems odd to me that all these things would go bad at one time. Do you have an idea.

What year and how many miles on the Tacoma? 4 cyl or 6?

Yes, unlikely it is ALL of those things. And certainly if you had bad coil(s), plug wires and plugs, the engine would be running rough, which it is not.

It could be as simple as a bad coolant temp sensor or a “lazy” oxygen sensor that is causing the computer to run the engine in a default rich condition.

Run away from the dealer and get a second opinion from a trusted independent mechanic. If you don’t have one, use the Mechanics Files here on Car Talk to find one in your area.

Your 21 mpg seems to be very good. Winter driving, change in fuel on sale in winter, and perhaps more stop and go local driving could bring your mpg down significantly. It seems you asked the dealer to get more mpg and they are going to throw every part in the book at it. Perhaps nothing is wrong.

How many miles on the truck? What is the maintenance history? Toyota generally recommends new plugs every 30K miles. Start simple, new plugs if they are have more than 30K miles and a new air filter. A bad coil would show up with rough running. All the sensors would throw a “check engine” light and a code stored in the computer.

Since you didn’t mention a check engine light I think the dealer is on a mission to empty your wallet.

Start with the very inexpensive things: 1) tire air pressure; 2) thermostat. If your truck has an automatic transmission, make sure it upshifts to the top gear. Finally, keep the $1875 in the bank to draw interest and wait until spring to see if the mileage improves.

4 cyl with 196k miles. I’m going to a local mechanic tomorrow and I’ll ask about the oxygen sensor. I’ll let you know. Thanks for the tip.

I had a 4 cyl Tacoma and always did much better than 12 mpg, even in winter, so you definitely have something wrong. You should be getting 18-20 around town, and better on the highway.

Triedaq posted below that it could also be a stuck open thermostat, so check that out, too. Much cheaper to replace than O2 sensors, etc.

Actually winter fuel has less oxygenate. The warm up cycle uses more fuel. Does the car start hard when cold out but the engine(warm) was run in the last 2 hours? That might be a bad coolant temp sender, possibly bad air temp sensor on the maf. The wallet issue is a given anytime they say it is more than one part. Bad coolant sensors will not throw a code until they report crazy temps but they will effect warm or semi warm starts and the initial warmup cycle.

bingo! I replaced the coolant temp sensor and check engine light came on again with codes for A/F sensor. Replace the A/F sensor (ala oxygen sensor at a cost of $168) and no more engine light and 23 mpg on last check. Thanks for hitting the nail on the head and helping me save at least $1500.