Lower MPG's after tune-up!?

[Surfcaster]

At 165,000 miles I do the following:

1. Replaced spark plugs/cables
2. Replaced PCV valve
3. Replaced fuel filter
4. Replaced air filter
5. Clean Mass Air Flow Sensor
6. Cleaned throttle body

Now I get 12 MPG!!! :wtf:

The 4runner defenitely runs better and with more power, but it used to get 17-19 MPG.

Any suggestions?

 

[JohnsD90]

You either developed a very heavy foot, or messed something up. What brand plugs and wires did you use? and what model? what fuel and air filter did you do? ...etc

 

[Surfcaster]

You either developed a very heavy foot, or messed something up. What brand plugs and wires did you use? and what model? what fuel and air filter did you do? ...etc

Plugs: Bosch 4301 Platinum +2
Wires: Bosch 09444 wire set
Air filter: STP SA7626
Fuel filter: Luber-finer FF692

These were what came up for parts at the Autozone store computer so I took them...prior to joining this forum.

 

[ryankmasuda]

I have a 99 SR5 V6 with the same mileage and I did a tune-up. Cleaned the MAF and PCV and I'm seeing the same results. However I did take my A/T's off and put some stock 07 Tacoma rims and tires on for the summer and I saw 15-16 mpg. I can't think of anything else to replace or service that will get my mileage up.

 

[JohnsD90]

Plugs: Bosch 4301 Platinum +2
Wires: Bosch 09444 wire set
Air filter: STP SA7626
Fuel filter: Luber-finer FF692

These were what came up for parts at the Autozone store computer so I took them...prior to joining this forum.

Some will say that the Bosch should never be used in this engine, and even if they are correct i doubt it is doing 5mpg off. I say clean the throttle body out good, and respray the MAF and make sure it is dry.

 

[Surfcaster]

Some will say that the Bosch should never be used in this engine, and even if they are correct i doubt it is doing 5mpg off. I say clean the throttle body out good, and respray the MAF and make sure it is dry.

Yeah, after some reading I am seeing that NGK is preferred for the plugs and wires and Bosch is to be avoided. But I agree, I don't see how that could be the cause of such a drastic MPG reduction.

I will clean the MAF and TB again and see if it helps.

 

[Clemsonfan15]

After I cleaned the TB and MAF I noticed the same trend, although in my case it could have been caused by the roof rack.

Did you pull the negative battery terminal? I wonder if the computer needs to be reset.

 

[Surfcaster]

After I cleaned the TB and MAF I noticed the same trend, although in my case it could have been caused by the roof rack.

Did you pull the negative battery terminal? I wonder if the computer needs to be reset.

I did not pull the negative battery terminal. I am going to the garage to do it now and let it sit over night.

This will be my first thing to try to correct it. Next will be cleaning the MAF again.

Thanks guys!

 

[98_4runnerSR5]

At 165,000 miles I do the following:

1. Replaced spark plugs/cables
2. Replaced PCV valve
3. Replaced fuel filter
4. Replaced air filter
5. Clean Mass Air Flow Sensor
6. Cleaned throttle body

Now I get 12 MPG!!! :wtf:

The 4runner defenitely runs better and with more power, but it used to get 17-19 MPG.

Any suggestions?

Seem to recently be having the same problems except for mine have developed after changing my fuel filter. No idea what the hell the problem is but it's really getting to me. Not getting 12mpg but getting 14-15 and used to get around 18... I have recently done all the same things as you in the past 5,000 miles so running out of possibilities. Working on figuring it out cause it's not good considering I'm trekking out to Colorado in a week to board :frog:

 

[Surfcaster]

Seem to recently be having the same problems except for mine have developed after changing my fuel filter. No idea what the hell the problem is but it's really getting to me. Not getting 12mpg but getting 14-15 and used to get around 18... I have recently done all the same things as you in the past 5,000 miles so running out of possibilities. Working on figuring it out cause it's not good considering I'm trekking out to Colorado in a week to board :frog:

What make and model fuel filter did you install?

 

[djbrand1]

Since it's probably getting colder where you live, the truck will use more fuel in it's warmup cycle as well as normal driving. Colder/denser air needs more fuel to keep the correct ratio. The benefit of that, is more power, tradeoff is lower MPG's.

 

[Surfcaster]

Since it's probably getting colder where you live, the truck will use more fuel in it's warmup cycle as well as normal driving. Colder/denser air needs more fuel to keep the correct ratio. The benefit of that, is more power, tradeoff is lower MPG's.

Thanks djbrand1, I will take that into consideration when trying to correct the problem.

 

[chris360hawks]

Well it doesn't help that you put garbage products in for the tune up....Go to your toyota dealer and buy the right parts, then see what you get.

 

[BTO]

It's probably the fault of the Bosch spark plugs. These engines are picky about the plugs.

 

[Surfcaster]

It's probably the fault of the Bosch spark plugs. These engines are picky about the plugs.

Yeah, I will be replacing them. Thanks for the advice.

Well it doesn't help that you put garbage products in for the tune up....Go to your toyota dealer and buy the right parts, then see what you get.

Absolutely. I won't make this mistake again. After joining this site, reading posts, and listening to the solid advice I have gained great insight regarding parts and service for my beloved 4runnner.

I am new to working on cars myself and have relied on the dealership and mechanics to do this work in the past. I have begun to realize this stuff is not nearly as intimidating as I made it in my mind. Not to mention how fulfilling it is to fix and care for your own vehicle and save money doing so!

Thanks for the advice I am doing one thing at time right now to single out the solution.

I will post updates as I move towards a solution.

 

[004Gunner]

Since it's probably getting colder where you live, the truck will use more fuel in it's warmup cycle as well as normal driving. Colder/denser air needs more fuel to keep the correct ratio. The benefit of that, is more power, tradeoff is lower MPG's.

Don't overlook this reply. It's important to note weather change (not the Al Gore type) and tire pressure before finding some other reason for decreased fuel economy.

 

[Surfcaster]

I have had some success!!!

The first thing I tried was the suggestion from Clemsonfan of reseting the computer (no time/no cost 1st):

1.) Disconnected negative battery terminal leads over night (longer than necessary)
2.) Reconnected, started truck, drove a few miles to highway and then went 10miles non-stop around 60mph avoiding high rpms.
3.) Drove truck a full tank after that. Mixed driving (city/highway/some 4WD-snow)

I now am up to 15 mpg's from 12, good improvement.

I will be replacing my BOSCH spark plugs with DENSO next and see what I get.

I am keeping in mind the effect of winter temps (and gas) and hope the MPG's only improve when warmer weather rolls around.

Thanks to everyone for the great input and suggestions, I have discounted none of it. I am taking each suggestion one a time to isolate the cause and possible solutions.

I will update after the DENSO plug replacement.