3.3TT MAP Sensor CEL

[Knowa]

2018 GT2 w/ 81k miles

Changed spark plugs 2 weekends ago because the old ones were starting to cause some misfires and timing issues with my JB4. Got them changed but now I am getting some pretty rough idling, with the occasional stumble down to 500 rpm or so and then a surge up to 800.

I got a P0106 (Manifold Absolute Pressure (MAP) sensor's range/performance) code to show up on my car a week ago, shut the car off and turned it back on and it went away so I figured I would just keep an eye on it. Now my idles are a little rough but after starting my car once today it was a really unhappy idle and felt like it was going to stall out and die. Restarted the car and it idled fine but about 10 seconds into driving the P0106 code came back and my infotainment system told me to service immediately.

Is there a place I should start looking on how to diagnose this issue? I read that it could be caused by a vacuum leak but all of my hoses look like they are in good shape and connected. Could it just be a bad sensor and me changing my spark plugs just it happened to coincidentally go out right after changing them out?

 

[Kodiack]

Did they remove your intake plenum when they did the spark plugs? Each cylinder has a gasket for the plenum and one might have been damaged.
If not pull the cover and look for hoses that might have come off or any visible leak.
Sounds like a vacuum leak to me.

 

[Knowa]

Did they remove your intake plenum when they did the spark plugs? Each cylinder has a gasket for the plenum and one might have been damaged.
If not pull the cover and look for hoses that might have come off or any visible leak.
Sounds like a vacuum leak to me.

Nope, I used a couple of jointed sockets to replace them and didn't remove the intake manifold at all. Perhaps I bumped a vacuum line somewhere while doing them? Is there an easy way of tracking one down or is it just a matter of checking every hose to make sure its connected and not leaking?

 

[Kodiack]

Only other way is a smoke test, they block everything off to atmosphere and smoke the intake.
If its a hard to find leak that might be the best bet.

 

[Deviate]

Have you tried cleaning the sensors? Ive changed both of my sensors but this last time i just pulled them out and cleaned them. MaSS air flow cleaner is what i used, code hasn't come back. Just a thought

 

[Knowa]

Have you tried cleaning the sensors? Ive changed both of my sensors but this last time i just pulled them out and cleaned them. MaSS air flow cleaner is what i used, code hasn't come back. Just a thought

I pulled both out and they were both clean as a whistle. I did clean out my injen air filters because honestly they were pretty gross and it seemed to drive ok for a week or so. Now when I start the car the idle surges up and down, so I think i actually do have a bad sensor. I have one on order to be here in a day or 2 so hopefully that fixes it.

 

[Deviate]

Are the injen filters oiled? Our sensors are not fans of oiled fiters from my experience, and random readings.

 

[oddball]

Oiled filters can affect MAF sensors, but they do not affect MAP sensors. Our car has 2 MAP sensors and 0 MAF sensors.
MAF sensors detect the mass of air flowing (m..a..f) by heating a small sensing element and detecting how much it gets cooled by the air flowing past it. Oil in the air stream will greatly affect how that cooling happens, which throws off the readings.

But we don't have an MAF sensors.

There's three fuel injection control schemes: alpha-N (minimal sensors, just how much cowbell?), speed-density (how much air based on MAP sensing) and mass airflow (how much air based on MAF). The degree and precision of control increases as you go up that ladder. The early fuel injection systems used MAP sensors because the processors at the time could only handle the complexities of speed-density control. As processors got better they could do the calculations for mass airflow, so the industry moved to MAFs and they became ubiquitous, hence why everyone talks about them all the time. A MAF is really hard to use with a turbo systems because air is whirling through the bypass/recirc valves and not necessarily going into the cylinders. Speed-density is much easier to use on a turbo car, and now the processors are fast enough to handle much more complex tables and algorithms so the OEMs overcome the old limitations with math and testing.



What all did you remove, move, unplug or modify when replacing the spark plugs? There are some weee tiny vacuum lines on the passenger side. The front right side of the intake manifold is actually a vacuum canister. There's also the vacuum lines running up to the switching solenoid and up to the recirc valves.


Anyway, this issue sounds like an air leak and isn't very likely to be an actual sensor issue. You need a good scan tool to read the live data to see what the ECU is actually seeing. A JB4 will actually tell you quite a bit in its logs, but the time resolution isn't high enough to do a lot of good. Seeing the different MAP readings can give you a clue to what exactly is going on. During idle the ECU expects both MAP readings to be the same. If one MAP is completely dead then either that sensor is dead (unlikely) or something happened to the wiring (much more likely). If one MAP sensor just has unreasonable readings then there's probably a mechanical problem like a leak. e.g. at idle the engine pulls anywhere from 12 inHg to 17 inHg vacuum in the manifold. The manifold sensor should see that, and the TMAP (in front of the throttle body) should see 0 inHg (local barometric pressure).
An old-fashioned "spray a bit of carb cleaner around all the parts of the intake track while idling and listen for RPM changes" test is your best bet here. Or a smoke test if you have a smoke machine. It is a little tough to cause an air leak on the Stinger because the air leak has to be *after* the throttle body in order to matter. But knocking one of those tiny hoses loose will *absolutely* do it.

Story time: I installed a boost gauge and tee'd into that line going to the vacuum canister. You have to be careful because there's one-way valves and whatnot also involved, so tap it in the right place. I used some cheap clear vinyl tubing that came with the gauge to run to a sensor I mounted on the back of the intake. Worked perfectly for ~2 years. One morning got in the car and it ran like CRAP. Surged, stumbled, total crap. Make it about 100 feet before turning around and parking it.
Popped the hood, poked around - a f'n rat had chewed on that vinyl tubing allowing a very tiny leak. Can't hear it, can't feel it. The openings for those lines are really small - maybe 1/16" - so it's not much air, but it's enough to really throw off idle.

There's also a good chance that something went wrong installing the spark plugs. Pull 'em and make sure they're OK. Heck, make certain the springs are in all the coil boots!!

P codes won't tell you what's really going on. I don't think there's even a standard P code for intake air leak. The ECU will throw codes based only on what it knows, so in this case it's saying the MAP isn't doing what it thinks it should be doing. That doesn't necessarily mean the MAP sensor is bad - that just means things are working the way the ECU expects based on the OEM's testing. And, well, and air leak sure as shit would cause that because the MAP would never read as low as the ECU is expecting. Like when it does fuel cutoff during decel the intake plumets all the way down to 22 inHg! (29.9 inHg is a perfect vacuum)

 

[Knowa]

What all did you remove, move, unplug or modify when replacing the spark plugs?

Just the plugs and coils, I use a couple jointed sockets so that I don't have to take the intake manifold off.

I did a visual inspection and I can't see or hear anything wrong with the vacuum lines I have been able to see but I feel like there may be one somewhere that I am missing. Unfortunately I only have a cheap chinesium scan tool and it's pretty lacking on the information that it can read. I did get my replacement sensor in and replaced the one behind the throttle body and that seems to have eliminated the surging after startup but something still feels 'off' when driving the car. I can't really put my finger on it but it just doesn't feel right.

Another thing I have been dealing with lately is my JB4 will not connect to the app while the car is running. I completely disconnected it at the instruction of support and was going to test everything with a multimeter to make sure that the MAP sensor connector was actually supplying power to the sensor, since from what I understand that is what the jb4 taps into for power. I should be able to test that connector by putting the car into accessories mode and just probing the pins with a multimeter, right?

 

[oddball]

No, the ignition has to be in 'run'. Tap the start switch twice (slowly) without touching the gas pedal.
You'd have serious problems if the MAP/TMAP power or ground was bad. I haven't looked in detail but those are usually shared with several sensors. If that's a problem then all kinds of hell would be breaking loose. It's a 5V supply straight from the ECU so no fuses.

 

[Knowa]

No, the ignition has to be in 'run'. Tap the start switch twice (slowly) without touching the gas pedal.
You'd have serious problems if the MAP/TMAP power or ground was bad. I haven't looked in detail but those are usually shared with several sensors. If that's a problem then all kinds of hell would be breaking loose. It's a 5V supply straight from the ECU so no fuses.

Yeah that would make sense that it would be a lot worse than what it is currently. I'd imagine if that was faulty it would be like having a low voltage battery where it just throws all kinds of codes.

I don't have access to a smoke machine, so carb cleaner/spray bottle of water is probably my best bet then. Do I just spray it around the joint between the upper and lower manifold and the vacuum hoses to check?

 

[Knowa]

No, the ignition has to be in 'run'. Tap the start switch twice (slowly) without touching the gas pedal.
You'd have serious problems if the MAP/TMAP power or ground was bad. I haven't looked in detail but those are usually shared with several sensors. If that's a problem then all kinds of hell would be breaking loose. It's a 5V supply straight from the ECU so no fuses.

So the first thing I tried was to pull the plugs and check for damage, everything looked fine. Plugs looked ok, coils were all seated and wires all connected. Didn't see any coil blowouts and no corrosion. Didn't expect this to be the problem but at this point in ownership it takes like <45 minutes to do plugs so I just figured why not.

So I investigated the Vacuum leak with a spray bottle of water and didn't find anything so I bought a cheap chinese smoke machine off amazon, which surprisingly worked pretty well, and found... nothing. No visible leaks, nothing out of the manifold, nothing down by the turbos... I used the vacuum line T'ing off right behind the throttle body.

Took the car over to a mechanic friend's place to look at and he thought that it's possible my purge valve was stuck open, which was causing the terrible idle right of start. Reasoning being that if the purge valve is stuck open and my intake is full of evap gas, when I go to cold start the AFR is wayyyy to lean for the plugs to ignite and my car was basically flooded. Well, $70 later, turns out it was not the purge valve...

With that information, it's leading me to believe that there's an issue with the fueling system of the car. Most recent thing I tried is to jump a bottle of redline in the tank and see if maybe I just have some gummed up injectors. Haven't driven long enough to get an exact idea but it seems better?

It's just so odd that the issue is sporadic. It doesn't seem to have any rhyme or reason why it appears. I will have some days where it cold starts fine, sits at a good idle rpm and never stumbles, and then some days the idle feels like a bag of bowling balls falling down the stairs. Some days when I give it a hard acceleration and let off the gas, I will get a pretty audible backfire, other days it's just fine. Some days it will throw that P0106 code 3-4 times, other days I can drive 150 miles that day in start/stop traffic and not experience limp mode a single time.

Anyways... It's still a mystery and we're still attempting to diagnose 3 weeks later....

 

[SiriusPilot]

Oiled filters can affect MAF sensors, but they do not affect MAP sensors. Our car has 2 MAP sensors and 0 MAF sensors.
MAF sensors detect the mass of air flowing (m..a..f) by heating a small sensing element and detecting how much it gets cooled by the air flowing past it. Oil in the air stream will greatly affect how that cooling happens, which throws off the readings.

But we don't have an MAF sensors.

There's three fuel injection control schemes: alpha-N (minimal sensors, just how much cowbell?), speed-density (how much air based on MAP sensing) and mass airflow (how much air based on MAF). The degree and precision of control increases as you go up that ladder. The early fuel injection systems used MAP sensors because the processors at the time could only handle the complexities of speed-density control. As processors got better they could do the calculations for mass airflow, so the industry moved to MAFs and they became ubiquitous, hence why everyone talks about them all the time. A MAF is really hard to use with a turbo systems because air is whirling through the bypass/recirc valves and not necessarily going into the cylinders. Speed-density is much easier to use on a turbo car, and now the processors are fast enough to handle much more complex tables and algorithms so the OEMs overcome the old limitations with math and testing.



What all did you remove, move, unplug or modify when replacing the spark plugs? There are some weee tiny vacuum lines on the passenger side. The front right side of the intake manifold is actually a vacuum canister. There's also the vacuum lines running up to the switching solenoid and up to the recirc valves.


Anyway, this issue sounds like an air leak and isn't very likely to be an actual sensor issue. You need a good scan tool to read the live data to see what the ECU is actually seeing. A JB4 will actually tell you quite a bit in its logs, but the time resolution isn't high enough to do a lot of good. Seeing the different MAP readings can give you a clue to what exactly is going on. During idle the ECU expects both MAP readings to be the same. If one MAP is completely dead then either that sensor is dead (unlikely) or something happened to the wiring (much more likely). If one MAP sensor just has unreasonable readings then there's probably a mechanical problem like a leak. e.g. at idle the engine pulls anywhere from 12 inHg to 17 inHg vacuum in the manifold. The manifold sensor should see that, and the TMAP (in front of the throttle body) should see 0 inHg (local barometric pressure).
An old-fashioned "spray a bit of carb cleaner around all the parts of the intake track while idling and listen for RPM changes" test is your best bet here. Or a smoke test if you have a smoke machine. It is a little tough to cause an air leak on the Stinger because the air leak has to be *after* the throttle body in order to matter. But knocking one of those tiny hoses loose will *absolutely* do it.

Story time: I installed a boost gauge and tee'd into that line going to the vacuum canister. You have to be careful because there's one-way valves and whatnot also involved, so tap it in the right place. I used some cheap clear vinyl tubing that came with the gauge to run to a sensor I mounted on the back of the intake. Worked perfectly for ~2 years. One morning got in the car and it ran like CRAP. Surged, stumbled, total crap. Make it about 100 feet before turning around and parking it.
Popped the hood, poked around - a f'n rat had chewed on that vinyl tubing allowing a very tiny leak. Can't hear it, can't feel it. The openings for those lines are really small - maybe 1/16" - so it's not much air, but it's enough to really throw off idle.

There's also a good chance that something went wrong installing the spark plugs. Pull 'em and make sure they're OK. Heck, make certain the springs are in all the coil boots!!

P codes won't tell you what's really going on. I don't think there's even a standard P code for intake air leak. The ECU will throw codes based only on what it knows, so in this case it's saying the MAP isn't doing what it thinks it should be doing. That doesn't necessarily mean the MAP sensor is bad - that just means things are working the way the ECU expects based on the OEM's testing. And, well, and air leak sure as shit would cause that because the MAP would never read as low as the ECU is expecting. Like when it does fuel cutoff during decel the intake plumets all the way down to 22 inHg! (29.9 inHg is a perfect vacuum)

Wow thanks for all the info!

 

[SiriusPilot]

Try going to a different gas station

 

[SiriusPilot]

I changed the OEM plugs to hks 2 days ago (no tune), having shakey idling at 1,200 rpm. It's really only right at that rpm. The plan is I bought another plug and kept the old coils so I'm gonna start on one and move down the line and see if I find the magic problem. If your issue started after the change maybe that could work for you. And if anyone knows how to take the whole fuse box off to get to the hydraulic unit under it for the love of God please help me. It's stuck in the back corner with these hoses and I can't get them off.