FrannyB

Hi All,

I am new to the 996TT world with a very stock '04 X50 cab with about 48Kmiles. We bought the car about a month ago from a private seller who always had the car serviced at a local dealership. I have quite a bit of history on the car and this P0507 code seems to pop up a bit. Previously, the dealer did a software upgrade to solve the problem. Other than that, they couldn't find anything wrong according to the work order. Since we have owned the car we have run a few tanks of gas through and have had the CEL rear its ugly head twice so far. The PO mention that he would get it occasionally, but he would fill it up with gas and it would go away. The first time it happened I took the car to the local FLAPS and had them read and then clear the code. I thought it might be related to a dirty air cleaner so I did a full oil change, fuel filter and new air cleaner. When removing the air box, I found the the large clamp was completely loose and just dangling. I figured that might be the cause as it is after the sensor. Well, it threw a code again yesterday so I decided to take out the intake plenum and perform a pressure test. Below is a photo of my very simple setup... I set the compressor to the lowest setting (pretty much zero psi) and just added enough air to get about 15psi with the larger black tube plugged with my thumb. ...and nothing... I even turned off the noisy shop lights and put the clock in the other room. I held the pressure for about five minutes and let it go and it rushed right out. So, I'm thinking I don't have anything amiss with the vacuum lines.

The idle on the car is a little strange. While at a light, for instance, it will slow to about 1000RPM and stay there for about a minute or more and then settle down to a bit above 800RPM and stay there. Next light it does the same thing. Other than that the car runs just fine and will boost up to 1 Bar.

So, first off, did I do the pressure test correctly? What else should I go looking for? I was really hopping for a popped out tube somewhere...

Thanks,

Franny

Kevin

If you are going to pressure test, you really need to install the test plug into the side intake plenum. That's where the airbox, MAF is clamped into.

Looks like you have a small leak OR your throttlebody is not shutting all the way due to carbon. I would clean the throttle and turn the ignition on then off and then on again.. Re-install your "Y" pipe and pressurize the intake to 15lbs.. Grab a spray bottle and mix dish soap and water, and check for leaks.

Here are the factory recommendations.

P0507
32 Idle air control at stop - above limit
Diagnosis conditions
• Start-up ended
• Speed = 0 km/h
• Throttle valve in idle position
• Engine temperature > 60 °C
• Intake air temperature > -10 °C
• No fuel tank ventilation or tank ventilation diagnosis
• No secondary air diagnosis
• Altitude correction factor > 0.75
• No faults in speed signal, throttle position sensor, engine temperature,
EVAP canister purge valve or tank ventilation system
Possible fault cause
♦ Throttle is jammed
♦ Leaks in intake air system

FrannyB

Thanks Kevin,

I'll go through this.

What do you think of cleaning the MAF? I wonder how that would send the idle past what could be controlled...

The PO said that filling the gas tank would make the CEL go away and, since the car was at 1/2 tank I gave that a try and sure enough, it turned off and stayed off... I guess I can look for a leaking gas cap... Seems more like coincidence to me though... Has anyone heard of this?

I want to go back in and clean the throttle and perform the leak test further upstream as you suggested.

Thanks,

Franny

FrannyB

Hi Kevin,

I pressurized just after the air box and I did find a small leak just after the left turbo. I cleaned all that up and it was just a loose clamp. Checked again and it seemed to hold pressure much better. I then drove the car and it wasn't any better/different So, I decided to take a good look at the throttle body and it was pretty filthy. Before I removed it, I turned the ignition on to watch its movement with the gas petal. It seemed to be a little jittery at the idle position. It would hum a bit and if I touched it, it would settle down and maybe close just a tad more (sort of like how the idle was behaving). I ended up pulling it off the car, cleaning completely and even lightly lubing the gears on the drive motor as well as cleaning the contacts (some photos below). I got it all back together and it did seem to be much better, but it is now gradually going back to hesitating at 1000RPM for several seconds or more before finally resting at a solid 880 or so. Once it is there it won't fluctuate and it sounds just fine, it just takes up to 15-20 seconds to get there and other times it goes straight to 880. I talked to the service manager at the dealership and he suggested cleaning the MAF. He said they replace quite a few of them - less on original airbox cars (like mine). I suppose I can try that. What is the sensor at the end of the "Y" tube? Is that also a MAF? He said if it was an O2 sensor, it would throw a code, but a bad MAF may not.

I might pressurize again just to be sure. I want to get a good pressure gauge so I can be super sure. Anything else I can try?

Thanks,

Franny

FrannyB

Another update... this time I built an actual pressure adapter with a gauge and a shut off valve from parts at Harbor Freight. I did find another leak... It is a hard plastic tube that runs from the right side of the plenum to the left and into a rubber boss on a part behind the alternator. It was way difficult to get to, but with the plenum off (again) I was able to get a clamp on it and it was solid after that. I put the plenum back in and tested again. I got a very small leak from a strange source; the MAP sensor. It seems to be leaking through its seams... I'm guessing this is not normal? It isn't bad, but what do you think? It seems to be functioning properly, just leaking ever so much.

I did take the car out and got it hot again and it is better, but there were a couple times the idle would just stay at 1000. Another it dropped to about 880 and then tried to climb back up a little. Super frustrating...

Any ideas? Comments?

Thanks,

Franny

Richard of CA/KY

FrannyB : I too am trying to resolve the issue causing the lone P0507 trouble code with my 2002 996 turbo. Check engine light (CEL) is on with only this trouble code.
I am wondering if you replaced the Manifold Absolute Pressure (MAP) sensor that you discovered slightly leaking thru its seams ? If yes, did the new MAP sensor solve your high idle and turn the CEL off ?

FrannyB

I didn't end up replacing the pressure sensor. I think it was just the "O" ring. On my car, it was just the MAF sensor. It passed the hot and cold electrical tests, but after mapping the throttle and MAF together it just looked off. I found a new one on Amazon I think for under $200 and gave it a shot. Totally did the trick! The car now idles on the tick and haven't had the smallest issue with the idle since.

Super bad of me to not follow up on this thread. Super sorry.

Franny

k9turbo

interesting to see a 7+ year old thread with resolution. reminding us all that idle fluctuation - while certainly indicative of a minor vac leak/dirty TB etc -

more often that not, is simply a faulty MAF. e.g. 750 rpm to 1000 idle with fluctuation and having the a/c on and having it stop the idle fluctuation?

swap out the MAF.

Richard of CA/KY

Replacing the hot-film MAF sensor with a brand-new and identical Bosch MAF sensor did nothing, unfortunately.
Next, I'll air-pressure test the entire intake via the rubber coupler boot for the engine's air filter housing box.
Service manual states to use no more than 0.5 bar (7.25 psi) for this test, so it'll need to be library-quiet to hear the hiss I hope to find.

Muskoka

I feel like any air-related fault code should result in a boost-leak test first and foremost. I wish I did that before shelling out $$$ on a new MAF.

k9turbo

^ i'm sure that's right. but last time i had idle fluctuation, i went with my gut and having had the issue before - and was lucky - it was just the maf.

don't forget possibly a dirty TB that isn't fully closing the butterfly. also a potential source of a minor leak.