FAQ: Mass Air Flow (MAF) Sensor Issues?

For a while I've had this code and couldn't find the problem.
I ended up replacing the MAF with one that I bought from another member here at rivperformance. The new one gave no change in code.This is a warning to anyone who has this code- check for vacuum leaks first.
I found my vac leak at the vac tee that goes into the LIM. nobody besides the dealer could get it and I had t buy the whole harness not just the tee.

here is the old and new tee's

i believe this is part number

i have the old one if someone needs a piece of it I paid about 27-28 $ for it

The code is gone now...
I'll just let the vac line go for nothin if someone is have a prob w thiers.

Can you tell me if they plug into the transmission modulator,vacuum tank, and two on the top of the engine? or a pic Thanks

the top end diagram fo a 96 l67 is different then my 98(the vac lines aren't the same)https://rivperformance.editboard.com/series-ii-engine-transmission-f4/series-ii-supercharged-l67-top-end-diagram-t84.htm
so i really dont think it will be the same for ur 95.
Ur still welcome t use anything it uve got a leak. i ll try t get a pic up soon

1-goes to the MAP sensor
2- goes to the LIM
3- goes to the fuel pressure reg(i think)
4- goes to the thingy right beside the bypass valve

Probably not the same as 95 I was just curious when I saw it where all the connections go on a 98. I would like to see a pic to see but there might be one already on here some where. Thanks for your answer.

can a broken mass flow air sensor make my car not start?

I don't believe so. The PCM can start and run the car without the MAF sensor.

I don't know TOO much about the sensor itself and it's complete functions, but once mine was unplugged after I changed my coupler and my car wouldn't stay running. I believe Turtle is more correct though.

What year is your car? Maybe, but it should run without it, albeit poorly.

it's a 95

Devins car would not start with a bad maf. try unplugging it and see if ti gets any better. Is the car trying to start, but it seems like the A/F is too far off to run? any SES light?

Can you change the title of this Topic to Mass Air Flow instead of Mass Flow Air for future search's.
I don't think anyone will search for a mass flow air sensor. (could be wrong though)

yes it's starting rough then stumbles off after about 10 seconds unless you give it gas but it runs really rough

That sounds like MAF to me. What result?

Well guys, I need your help on a code that's been stumping me today. I had a few ideas instantly, but not 100% sure, so I want to hear what you think based on the description of the problem. Here goes...

As I approach 195k miles, I noticed a few weeks ago during a WOT run - audible knock - last time I heard that sound, it was the result of running a 160º t-stat before tuning the KR sensor activation value. So, I figured this could be a disconnected sensor, but haven't been working on the engine at all, so kinda weird.

I took it easy for a while, and the car drove fine for most driving, but again when I go into boost - I could hear the knock. I continued to take it easy.

Today I found some time to scan. Saw two P0171 codes logged, which I've never seen before, and a glaring LTFT value of +16.4 (maxed!). I can put the car into cruise at 70 mph, and the LTFT will stay pegged at +16.4 constantly. At even gentle levels of boost, KR comes on fast. 5º KR is pretty easy.

So what is everyone's gut feelings on this? I'm hoping some of you will think of something I haven't. I can give more information as needed, but I was hoping someone had seen this exact problem and knows the fix.

Thx for any help!

still using the stock MAF and 02 sensors w/195k miles?

Well i saw you mention in another thread that your LIM gaskets are failing, maybe they're letting unmetered air into the cylinders and causing a lean condition.

Mr.Riviera wrote:

still using the stock MAF and 02 sensors w/195k miles?

I agree, my first thought was MAF. MAF sensor is original. May need cleaning or replaced. Anyone know how to visually identify bad MAF sensor? O2 sensor has been replaced twice, last time with AC Delco ~100k miles ago (3 1/2 years ago).

Quote :

Well i saw you mention in another thread that your LIM gaskets are failing, maybe they're letting unmetered air into the cylinders and causing a lean condition.

That's correct, this is a known problem. However, the car runs great at idle and under throttle, except for the knock. I'm not sure, but would the LIM leaking air give the same results as a vacuum leak? If it didn't idle so smoothly, I might be leaning more this direction. But i've had a vac leak before that caused +16.4 LTFT, and it caused the engine to consistently stall at idle.

Good ideas, guys. Thanks for the tips! So far on the list: 1) MAF sensor, 2) O2 sensor, 3) LIM gasket

Anything else? If not, which are we leaning toward most and why?

One more clue: LFTF recovers slightly to +6.3 on decel from cruising. It will do this consistently.

AA wrote:

Mr.Riviera wrote:

still using the stock MAF and 02 sensors w/195k miles?

I agree, my first thought was MAF. MAF sensor is original. May need cleaning or replaced. Anyone know how to visually identify bad MAF sensor? O2 sensor has been replaced twice, last time with AC Delco ~100k miles ago (3 1/2 years ago).

Quote :

Well i saw you mention in another thread that your LIM gaskets are failing, maybe they're letting unmetered air into the cylinders and causing a lean condition.

That's correct, this is a known problem. However, the car runs great at idle and under throttle, except for the knock. I'm not sure, but would the LIM leaking air give the same results as a vacuum leak? If it didn't idle so smoothly, I might be leaning more this direction. But i've had a vac leak before that caused +16.4 LTFT, and it caused the engine to consistently stall at idle.

Good ideas, guys. Thanks for the tips! So far on the list: 1) MAF sensor, 2) O2 sensor, 3) LIM gasket

Anything else? If not, which are we leaning toward most and why?

One more clue: LFTF recovers slightly to +6.3 on decel from cruising. It will do this consistently.

Might as well check the oil too, if milky (hope not ) then you know the gasket is down the toilet. If not then it might be more beneficial to start somewhere easier like the MAF.

Good idea. I just changed the oil last Saturday. Nothing unusual. Since my oil was analyzed by Blackstone a little over a year ago, I've been changing oil at 2500 mile intervals (they recommended 3k). I am loosing very little coolant from this LIM leak. As far as I know, it has only effected cylinders #2 and #6. I will check plugs soon to see if the condition has advanced, adding to list...

1) MAF sensor, 2) O2 sensor, 3) LIM gasket, 4) spark plugs

AA wrote:

Good idea. I just changed the oil last Saturday. Nothing unusual. Since my oil was analyzed by Blackstone a little over a year ago, I've been changing oil at 2500 mile intervals (they recommended 3k). I am loosing very little coolant from this LIM leak. As far as I know, it has only effected cylinders #2 and #6. I will check plugs soon to see if the condition has advanced, adding to list...

1) MAF sensor, 2) O2 sensor, 3) LIM gasket, 4) spark plugs

Could also check general vacuum lines and fittings, although for a leak of this nature it would seem that multiple lines would have to be loose or disconnected. But if you've been digging around in the engine bay anytime lately you may have aggravated some brittle lines and caused some cracks. This happened to my car as the CPS wire was being repaired, now the damn thing wont start!



Never hurts to take a look around to see if there are any obvious vacuum line issues.

I'm also leaning towards a vacuum leak. Can you take a detailed scan?

When's the last time you changed your fuel filter? Could be a fuel delivery problem of some kind... still stock fuel pump? Did it just start happening this tank of gas? Maybe the gas station has bad fuel? (wouldn't be the first time for that!) Did they slip you some E-25 instead of E-10? I've heard of that happening before, the ethanol ratio was screwed up... or maybe it's E85...

deekster_caddy wrote:

When's the last time you changed your fuel filter? Could be a fuel delivery problem of some kind... still stock fuel pump?

after sleeping on it some this is my second guess.
Do you have a way to monitor fuel pressure? Any chance you got a tank of dirty gas and the filter is clogged up?

I was suspecting a vac leak, but as I said, car runs great. Nice and smooth. I have not touched the engine lately. But I will put it on the list.

Fuel delivery could be a problem as well. Does it make sense that even under almost no load (cruise/idle) I'm maxed at 16.4 LTFT? That would seem like a serious fueling problem, as it shouldn't take much fuel to keep up with such low demand. I haven't changed fuel filter in 40k, so I will do that. I also will measure fuel pressure at the rail.

I did fill up with a new tank of gas recently, but the codes for lean condition have been occurring for days or weeks, so I hardly think that's it.

We have a good list going now (anything else it could be?):

1) MAF sensor
2) O2 sensor
3) LIM gasket (check spark plugs)
4) vacuum line leak
5) fuel pressure
6) fuel filter