Check Engine Light + Codes After MAF/Throttle Body Clean

R

rocky.mtn

New member
Hi All
Feel sick to my stomach after I undertook the cleaning of the MAF and throttle body on our new to us ‘99 4Runner.

I removed and reconnected what I think is everything but after about 15 minutes got a check Engine light after turning the ignition back on after stopping.

I figured maybe the ecu need a reset so I pulled the negative terminal and EFI fuse. The check engine light stayed off even after a very rough idle (which I assume is idle relearning after the efi fuse pull) and then came back again after 20 minutes of driving. Engine light seemed to come back again after an acceleration?

There is nothing noticeably weird going on, and power seems just fine, but i do need to get this solved.

Current codes are:
P0015
P0123
P0301
P1693

I’m really hoping this is a connection issue which i will go back through - but is there a logical place to start here?

Thanks for any help here.
 
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Just a crazy, wild guess; did you mix up the IAC's vacuum and coolant line? Assuming the throttle body was taken off the engine.
Would explain the misfire code and why it happens more so on acceleration.
 
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Did you pull the codes before you disconnected the battery or after? If before, did they all come back after or only some of them?
 
Ok so I retested with OBD fusion and am only getting a single code now which is P0171. This is with the key in the on position, but ignition off.
 
P0171 is typically a dirty MAF. When you cleaned it, did you let it air dry for a bit or did you spray it and toss it right in? Sometimes when people don't wait for it to dry completely it supposedly likes to trip out for a little while. I've personally always doubted this because MAF cleaner evaporates immediately, but it's definitely something I've seen said more than once so perhaps theres truth to it.
 
Per the FSM, these are the possible causes of the P0171 (System too lean):

Air induction system
Injector blockage
Mass air flow meter
Engine coolant temp. sensor
Fuel pressure
Gas leakage on exhaust system
Open or short in A/F sensor (bank 1 sensor 1) circuit
A/F sensor (bank 1 sensor 1)
ECM

Given the work you just did, I'd focus on looking for a vacuum leak as has already been suggested as the most likely cause followed by an issue with the MAF. The rest of the list are unrelated the the work you did, so they would be coincidental problems rather than caused by the work you just did.
 
Skulking said:
Per the FSM, these are the possible causes of the P0171 (System too lean):

Air induction system
Injector blockage
Mass air flow meter
Engine coolant temp. sensor
Fuel pressure
Gas leakage on exhaust system
Open or short in A/F sensor (bank 1 sensor 1) circuit
A/F sensor (bank 1 sensor 1)
ECM

Given the work you just did, I'd focus on looking for a vacuum leak as has already been suggested as the most likely cause followed by an issue with the MAF. The rest of the list are unrelated the the work you did, so they would be coincidental problems rather than caused by the work you just did.
Click to expand...

Thanks I have tried pushing all the vacuum hoses firm against the fittings and taped the cracks at the ends on some of the small ones.

Took out and cleaned the MAF again and cleared code. Code stayed off for a quick 10 minute drive this morning, but it may not have been long enough. Will test again.

I guess there is a potential that I could have damaged the MAF during the cleaning, touching with the straw or something.
 
rocky.mtn said:
Thanks I have tried pushing all the vacuum hoses firm against the fittings and taped the cracks at the ends on some of the small ones.

Took out and cleaned the MAF again and cleared code. Code stayed off for a quick 10 minute drive this morning, but it may not have been long enough. Will test again.

I guess there is a potential that I could have damaged the MAF during the cleaning, touching with the straw or something.
Click to expand...

If'yours is damaged this is a good price for a used densone. clean it before'you put it in but 20 bucks is a good risk.
https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/383615150827
 
So I re-ran at lunch and the P071 returned. Seems it is always returning on the second trip after clearing it with OBD Fusion.

I did take some readings:
Warm Idle 597 RPM @ 191 F Engine Temp
MAF 0.37 lb/min @ Idle
Fuel % Trim Bank 1 - 19.5%

I'm guessing the MAF is too low and fuel % is too high? Even though idle RPMs appear normal.

Struggling to figure out how to nail down if this is a MAF or Vaccuum issue now. I may just buy a new MAF (even though they are darn expensive in Canada) and then re-dig around vaccum lines tonight.
 
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rocky.mtn said:
So I re-ran at lunch and the P071 returned. Seems it is always returning on the second trip after clearing it with OBD Fusion.

I did take some readings:
Warm Idle 597 RPM @ 191 F Engine Temp
MAF 0.37 lb/min @ Idle
Fuel % Trim Bank 1 - 19.5%

I'm guessing the MAF is too low and fuel % is too high? Even though idle RPMs appear normal.

Struggling to figure out how to nail down if this is a MAF or Vaccuum issue now. I may just buy a new MAF (even though they are darn expensive in Canada) and then re-dig around vaccum lines tonight.
Click to expand...

P0171 has 2 trip detection logic, so after you clear it it shouldn't come back until your second trip.

Converting your MAF reading to g/s I'm getting 2.8g/s. I believe that is within the normal range, but possibly on the low side. Given the fuel trim you are showing it looks like your injectors are dumping as much fuel in as they can to try and get your AFR correct and they can't do it. It's possible that your MAF is reading low and you actually have more air flow than it is measuring, but at this point I'd still be leaning towards vacuum leak.
 
rocky.mtn said:
So I re-ran at lunch and the P071 returned. Seems it is always returning on the second trip after clearing it with OBD Fusion.

I did take some readings:
Warm Idle 597 RPM @ 191 F Engine Temp
MAF 0.37 lb/min @ Idle
Fuel % Trim Bank 1 - 19.5%

I'm guessing the MAF is too low and fuel % is too high? Even though idle RPMs appear normal.

Struggling to figure out how to nail down if this is a MAF or Vaccuum issue now. I may just buy a new MAF (even though they are darn expensive in Canada) and then re-dig around vaccum lines tonight.
Click to expand...

To clarify are you showing +19.5% (positive) or -19.5% (negative) fuel trim?
 
I put my gasket on incorrectly for the throttle body and that was the cause for me.

If your sensor is reading correctly you have air bypassing the sensor.

I found my issue with the gasket spraying brake cleaner.


Sent from my iPhone using Tapatalk
 
rocky.mtn said:
Thanks.
OBD Fusion isn't showing me a sign notation, so I think it would be positive?
Click to expand...
If it is a positive fuel trim then the engine is trying to compensate for unmetered air. Did you remove any vacuum lines when you did the repair? If you did verify they are in the correct location and seated properly. An easy way to check for vacuum leaks is to take carb cleaner or starter fluid and spray different areas of the engine/intake/vacuum hoses and listen for an idle change. It works best once the engine warms up and the idle drops. Unfortunately if it is a vacuum leak that will affect the flow of air through the MAF sensor so a low MAF reading won't necessarily tell you the MAF is bad or not. You can also see if someone has a known good working MAF that you can borrow. I believe 96-98 use a different MAF sensor than 99-02.
 
.518 lbs/min is what both 97s run with a warmed up idle in park or neutral. It was .390 with the gasket installed incorrectly.


Sent from my iPhone using Tapatalk
 
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