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The check engine comes on with the air filter in place. But…

Customer Question
The check engine comes...

The check engine comes on with the air filter in place. But when I remove the air filter the check engine light comes on? Why ?

Mechanic's Assistant: Does the light stay on, or does it blink?

Stays on solid with the air filter in place

Mechanic's Assistant: What is the make/model/year of your car?

2000 Toyota Tacoma 3.4L ca. auto trans

Mechanic's Assistant: Are you fixing your Tacoma yourself? What have you tried so far?

Yes. code 171 said to replace the 02 and the mas air flow. And I did replace both.

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

Yes the truck runs great with or without the air filter. No check engine light comes on if I keep the air filter out. ?

Submitted: 7 months ago.Category: Toyota
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Answered in 29 minutes by:
12/2/2017
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 7 months ago
Ted Ritter
Ted Ritter, Toyota Master Tech
Category: Toyota
Satisfied Customers: 4,711
Experience: Toyota Master Tech, ASE Certified
Verified

Thanks for posting

Does it have an aftermarket cold air intake system?

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Customer reply replied 7 months ago
everything is factory
Customer reply replied 7 months ago
no everything is factory
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 7 months ago

T​he P0171 code can also be caused by a leak on the intake between the air filter and throttle body, could be restriction in the air filter box or the air filter itself, have you tried a new one?

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Customer reply replied 7 months ago
still the same
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 7 months ago

Very odd. When the air filter is installed and you start the engine does the check engine light turn on right away or does it take a while of driving?

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Customer reply replied 7 months ago
no with the air filter in place it will take about 25 miles before the light comes on
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 7 months ago

90% of the time the P0171 is caused by a dirty or contaminated MAF sensor, have you checked the sensor electrical connector for any signs of wire damage or corroded pin connections?

The air filter (all air filters) restrict air flow a little by design, in your case it seems there is more of an air flow restriction and it has to be before the MAF sensor to affect it's operation. check the air inlet before the air filter for any foreign objects.

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Customer reply replied 7 months ago
I have taken the entire air filter box and everything is clear and out as it should be. no restrictions in the air box
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 7 months ago

I​s there another maf sensor you can try? did you use an aftermarket part?

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Customer reply replied 7 months ago
no and no
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 7 months ago

It may be an ECM issue then, how did this start happening? Was anything else done to the engine before this came up?

There is a ground connection on the intake with a few brown wires fastened by a 10mm bolt, these are computer grounds, make sure the ground connection is good.

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Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 7 months ago

Check all small vacuum hoses,

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Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 7 months ago

Besides what I have suggested so far the problem could also be caused by an evap purge valve malfunction but you should also be getting an evap code as well.

You can try blocking the purge valve off, it has the green cap on it and has intake vacuum to it at all times, block the hose to it off and see what happens.

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Customer reply replied 7 months ago
ECM or grounding ? when a air filter makes the differences ? and no codes set with the air filter is out. What code is for the evap?
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 7 months ago

Evap codes are usually P0441 or 442 for small leaks.

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Customer reply replied 7 months ago
well no clear answer on this one. So thank you.
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 7 months ago

I will opt out and maybe someone else here has an answer for this.

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Toyota Mechanic: sprinkles08, ASE Certified Technician replied 7 months ago
sprinkles08
sprinkles08, ASE Certified Technician
Category: Toyota
Satisfied Customers: 24,064
Experience: ASE Master and Advanced level certified. Factory trained with 17 years dealership experience
Verified

Hello and welcome to JustAnswer! I apologize for the extended wait time you experienced, I've only just come online now and would like to assist you with your question.

P0171 sets when the engine is running lean. There are several possible causes for this including vacuum leaks and some things already covered, but there is a good chance fuel pressure is low. Has fuel pressure been monitored under a load?

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Customer reply replied 7 months ago
No. The onboard diagnostics has no stored codes. After complete Diagnostics and visual inspection everything was found to be correct in a good order. The scanner reports that the 02 and the EVAP system have completed their readiness. the only thing remaining is the catalytic converter on board diagnostics have not been activated or completed.
So I must drive it according to the Toyota drive cycle. Once the on board diagnostics for the catalytic converter readiness has been accomplished there should be no more problem. With or without the air filter? Does that make sense?
Toyota Mechanic: sprinkles08, ASE Certified Technician replied 7 months ago

I don't follow. Your question was about the check engine light coming on with a P0171 set.

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Customer reply replied 7 months ago
No
Toyota Mechanic: sprinkles08, ASE Certified Technician replied 7 months ago

This is the question you posted:

the check engine comes on with the air filter in place. But when I remove the air filter the check engine light comes on? Why ?

Mechanic's Assistant: Does the light stay on, or does it blink?

Stays on solid with the air filter in place

Mechanic's Assistant: What is the make/model/year of your car?

2000 Toyota Tacoma 3.4L ca. auto trans

Mechanic's Assistant: Are you fixing your Tacoma yourself? What have you tried so far?

Yes. code 171 said to replace the 02 and the mas air flow. And I did replace both.

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

Yes the truck runs great with or without the air filter. No check engine light comes on if I keep the air filter out. ?

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Customer reply replied 7 months ago
That's what I was told.
But because you must refer to another.
And all the time that passed by.....
I looked into it my self and found the answer I gave when you stepped in.
Sorry thank you. But I found my answer myself sooner. Best regards.
Toyota Mechanic: sprinkles08, ASE Certified Technician replied 7 months ago

I'm glad you got it repaired.

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