Hi All,

An introduction and some questions...

I am new to this group with an '04 X50 Cab we bought a couple months ago with 47Kmi. The car is bone stock and runs well and pulls strong at 1Bar, but the idle is high when the car is fully warmed up.

So, here is what is happening: The car idles on the tick when cold - just below 800rpm. It is stable (of course a little high right at start-up, but still below 1000rpm) Once the car is fully warm (like when you can check the oil) the idle won't settle down from 1000. Then after several tries, it will throw a P0507 Idle past stop. I have also noticed that if the cooling fans turn on, it will go right down to just below 800 but when they stop, it will climb back up to 1000+ and hunt a little.

Here is what I have done so far: I preformed a pressure test (removed the airbox and attached there) and found few small leaks which I was able to fix (a loose vacuum line, loose turbo output, and the pressure sensor). When I got the car, one of the large hose clamps on the air-box was completely loose (I was hoping that was it). All that has been fixed and it will hold pressure from just after the air box just fine (~10PSI). I have also removed and completely cleaned the throttle body. It was pretty dirty. I cleaned the wiper contacts and lightly greased the gears.. I pulled and cleaned the MAF sensor with electronics cleaner. It seemed just fine. I cleaned the pressure sensor on the intake plenum and replaced the "O" ring (it was one of the air leaks). I replaced the air cleaner element.

At this point I'm not sure what to do next... If I remove the oil cap at idle the idle will increase a bit and goes back down a bit when I put it back on. I keep wanting to think it is the throttle body just not settling back down, but I have tried lightly tapping on it with the plastic end of a screwdriver when the idle is high and that does nothing. If it holds pressure I'm assuming no vacuum leaks... Weird how it reacts to the fans though... In the service records, the car had been to the dealership a couple times for this issue at about 20K miles. They cleaned the TB and "reprogrammed". The PO said that it has been doing this for a while, but the CEL always re-sets itself when he fills it up with gas so I think he just got used to it. None of this was found during the PPI

I guess the two possibilities at this point are the MAF and the throttle body? They are pricey to play parts roulette with though. The symptoms seem pretty specific and repeatable... What are my next steps?

In a hopefully unrelated issue, after the car gets hot and sits in the garage or is idling, it seems to overflow windshield wiper fluid... If I pull the cap under the hood you can see the level rise and fall dramatically. The leak is just forward of the driver's door - about three or four ounces. I know this is where the accumulator will spill too, but this is water with a blue tinge and not brake/hydraulic fluid. It evaporates off the driveway.

I also have a weeping right front radiator so I will be replacing all three with those super-cool aluminum ones when they get here next week.

Thanks so much,

Franny

Sorry, but this is not bone stock. Find out what flash you have and perhaps it needs adjustment.

Thanks Wross,

It is my understanding that the X50s boost to 1bar from the factory. Is that not true?

Franny

Congrats on the car. Sorry to hear of the problems. What does the car do when you put the A/C on? There is a vacuum line that goes up to the charcoal canister/ gas tank, one of the valves up by the gas tank may have failed? You can disconnect and cap in the engine bay easily. I will get a pic up of it later today.

If you catch all the leaks in the intake air system it can be related to the fuel tank ventilation system according to the OBDII manual… If you got access to Durametric there are a couple of valves you can check in the system for proper operation...

Ya know, you guys might be on to something... What would you expect to happen if you remove the gas cap while the engine is running (warmed up)? I tried that and got nothing. No rush of air, no change on idle and no difference if I put my palm over the opening. I expected some change.

Tim, if you can find that photo that would be awesome.

Thanks guys,

Franny

May be this will help you located the pipes going to the tank and the valves. They are under the right front wheel well liner. One is located besides the filling pipe and the two others are a bit in front of it….I remember not long time ago helping someone with one of those valve found at fault. But cannot found the thread ;-(

Thank again, I'll pull the liner and have a look.

Looks like I may have to invest in the Durametric software.

Franny

Ok here is some pics. The line has a check valve on it so a boost leak test will not show anything even if the line can by wide open on the other end, under vacuum it is a leak tho.

The line, press in the two grey tabs to release.



Released.



Cap off the engine side.



See if that drops your idle.

Ok, I have some results...

Tim: If I remove and plug that line (thanks so much for the photos), it makes no difference Now, I do feel a nice strong vacuum on that line so that is a plus, but in no way could I notice a difference (revving a few time and holding at 3K for a few seconds and then to idle)

I tried the AC and, boom - right to the correct idle and holds through several revving (my neighbors must love me...). I turn the AC off, it goes right back up to ~1000K and hunts a little.

If the rear deck lid fan fires up, no change, but if the two front radiator fans turn on it settles right down to the correct idle and stays put.

Does any of that help? Sounds a little sensor-y... I would think a leak would mess with the idle across all different scenarios, no? Maybe with the AC or the front fans on it bypasses some system/sensor?

I haven't done the bit under the right wheel because I don't have the Durametric kit. Can I check them without it? Maybe just 12V to the appropriate pins? Looks like one is in my future. Seems like it is a must with this car (or a strong want).

I actually feel a little better eliminating things and seeing it actually work properly in certain conditions...

Thanks for your suggestions! Any more ideas from here?

Franny

Ok. It is a vacuum leak. Once you have a load on the engine the Leak is providing enough flow that the T/B at its stop is enough to control the idle. Try the brake booster line next. It is right behind the line you just opened. You will need to remove the grey clip (on a white coupling) in order to separate the coupling. All these lines have check valves the boost leak testing will not show the leaks.

Ok, so I found what your were describing, removed the gray clip and there was even a little wush of air (engine off...) when I pulled the tube out. I replaced the tube, but not the clip and went out to warm it up again. Got back and pulled that tube - lots of vacuum! The car almost stalled and I sealed it with my rubber gloved finger. No real change. I had someone run the rpm up and down a couple times with it connected and with my finger on it and no real difference. Tried the AC thing again and the idle went down. Put the tube back on and reinstalled the clip.

I'm guessing when I find it it should be pretty obvious, right?

Thanks again for all your help!

Franny

Tim,

Do you think there is any possibility that the TB is just inaccurate at the very extent of idle and with the AC on, it has to open a little more getting it out of the bad spot? Not sure why it would be bad just at idle though...

Any ides on what to check next? Maybe some of the valves under the fender well as JP suggested? Can I check them the same way as the other two?

Thanks,

Franny

Hi All,

I spent a bunch of time yesterday going back over everything and I just can't seem to find the smoking gun...

I disconnected the two vacuum lines detailed above (Break Booster and not sure what the other is for) and capped them off really well. I went for a drive (no brake assist, so I was really careful) and got the car good and warm and no change in behavior. Still idling at 1000 and sometimes drops down - but only when hot (cold the car idles just fine). Re connected the lines.

I pulled the intake plenum and stared at the TB hoping I would get some inspiration. I had someone operate the throttle a bit and it moves smoothly, but at idle it hums for about 10 sec and then stops with a slight movement closed and then is quiet. It does it every time...

Then I pulled the TB again just to double check. It seemed just fine, but I lubed the big drive gear this time. It is a compound piece with and internal coil spring in addition to the main return spring all functioning to get the rest butterfly position to be open just a smidge. In the resting position, the butterfly is open a bit (you can see in the above photos); maybe 1mm or so. You can push the valve completely shut, but you are pushing against the secondary spring. The movement there is not very smooth... Like two pieces of plastic rubbing against one other. I got a little white lithium grease in there and it felt slightly better. I cleaned the gasket seal and pulled the gasket out and turned it around. I'll replace it next time I'm in there, but it seemed and felt just fine.

I put it back on the car and checked it's movement again with my helper. No change there... ...still had that 10sec pause with the hum at idle and then slight close and silent. I re-installed the intake plenum.

I did another pressure test at the junction of the airbox. At 15psi it would hold pressure only loosing about 2psi a minute. I think that is pretty good. The problem is that it doesn't test vacuum though, but with the large two vacuum lines ruled out that leaves only one line I'm wondering about. Number 19 in the diagram. Where does that go and can I isolate it to be sure it isn't an issue?

So, I got the car all back together and went out for my normal drives. The idle was just fine even once it got warm. We drove it to work today (a better test with a bit of stop and go) and it was idling at 1000 for a few seconds and then dropped down to normal (700-ish?). When it got to 700-ish it would stay there. Can I rule out a leak and focus on the TP or am I still hunting down some leak somewhere? I'm not sure what to check next.

I guess this is a dumb question, but what is "normal"? Should it always return to the 700-ish immediately or does it step down sometimes over a few (3-8) second time period? I can see it doing that to allow the turbos to spool down a tad. Also, in the service records the dealership did "re-program" the TB so I'm wondering if they added this pause...

Thanks again,

Franny

this may be the dumbest suggestion given the expertise the experts are sharing with you but..

as near as i remember, every time you disconnect the maf, you should allow the ecu to reset the TB. turn ignition to on position approx 30 seconds, until you hear the tb reset. than start as per usual. it can't hurt though any idle hunting ( to 1k .. then back down to 750/800 or a/c "on" to normalize ) i've ever had was a vac leak for sure.

add: no "step down" on idle. should be 750/800 always.