What’s your idle MAF reading?

[19963.4lsr5]

I’m chasing a P0171 and my MAF reading at an idle of 700rpms in park is around .390 lbs per min.

The Ex’s is reading .518 during the same conditions. Which is leading me to a vacuum leak but my engine is not idling high at all. It’s 650rpm in gear and 700rpm in park or neutral. Plus I’ve sprayed the crap out of everything I could with brake cleaner and no idle change.



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[4Runner4Leon]

I haven't looked at my MAF readings, but my LTFT is around 10%, which is higher than I'd like it to be. Yours being 29% says that it's running very lean. I know you've checked for vacuum leaks, but maybe it's not getting enough fuel through the injector(s), thus causing the lean condition.

 

[Joelzy]

Sounds exactly like my vacuum leak when i first got my motor back together

I was running 18.8% LT and had a code as well

Could not for the life of me find the leak, tried smoke testing with UV and all.
Eventually saw the tiniest bit of smoke under the manifold but never determined if it was an injector ring(not likely) or the manifold to head gasket(probable) but they were both brand new so i was unhappy either way.

replaced both since i had to go that far back in regardless and voila!

worked great for about 40 miles when it popped an 02 sensor code.

 

[19963.4lsr5]

Joelzy.

Your second reading after the gaskets were replaced in G/S converted to lbs/min line up with the .518 lbs/min of the puppy hauler with the fuel trims at 0 warmed up at idle.

It sure does seem like I have a vacuum leak somewhere. But I sprayed the crap out of everything I could get too no idle or LTFT change.


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[Joelzy]

Joelzy.

Your second reading after the gaskets were replaced in G/S converted to lbs/min line up with the .518 lbs/min of the puppy hauler with the fuel trims at 0 warmed up at idle.

It sure does seem like I have a vacuum leak somewhere. But I sprayed the crap out of everything I could get too no idle or LTFT change.


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i did the same and got no reaction because of where my leak was coming from. I feel your pain, it was driving me bonkers and i needed to pass inspection


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[19963.4lsr5]

i did the same and got no reaction because of where my leak was coming from. I feel your pain, it was driving me bonkers and i needed to pass inspection


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Well it’s looking like I’m going to either try and retorque the intake manifold and replace the plenum gaskets or I’m going to pull the intake and start over. I was as carefull as I could be installing it. And the heads were barely touched to resurface them. It’s not like I had .025 shaved off them to raise compression or something.......


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[LittleCaesar]

.40 here with zero problems to report. I did replace my MAF about five years ago after I learned that the PO’s grandson had tried to clean the MAF but somehow had bent the IAT sensor.

 

[19963.4lsr5]

.40 here with zero problems to report. I did replace my MAF about five years ago after I learned that the PO’s grandson had tried to clean the MAF but somehow had bent the IAT sensor.

Then it’s retorque the manifold or pull it and do it again with new gaskets.


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[19963.4lsr5]

So .518 lbs/min on the MAF sensor is a good number at idle in park or neutral at 700rpms.

Anything less is vacuum leaks

My issue was I didn’t put the throttle body gasket on in the proper position I did tighten all the bolts on the intake manifold first. Same .390 lbs/min after so I looked elsewhere


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[Hopeless Diamond]

Here's a way to calculate what your actual MAF reading should be (grams/second). It will vary based on altitude and barometric pressure at the time. Keep in mind, as they state, the OBD reading isn't real time and will lag.

engine theory - Is there anyway a shade-tree mechanic can check MAF calibration? - Motor Vehicle Maintenance & Repair Stack Exchange