I took the car for a drive, and the code came back very qickly (about 1 mile).
As I forgot to take the 10mm spanner I need to disconnect the battery, I drove back, cleared the code again, and went back driving.
I drove about 40km (30 miles) mostly in town and short motorway: the code didn’t came back
Idle is still wrong (lumpy enough you can see the engine moving) and too fast : 850rpm on D, 1100 rpm on N or P (both hot, and AC was on too)
I reckon next step is to take the spark plugs ou and compare them to find which cylinder(s) are involved
I’ll wait for the engine to cool down before doing so, so probably a few days to come back
And finally, your FF34 is most certainly a fault in the O2-sensor one the A-bank.
Fix the vacuum leaks and adjust the idle screw, unplug BOTH O2-sensors and try it.
Disregard the FF44/45 codes. Engine runs perfectly fine in open loop with no feedback.
Idle should be smooth.
After driving a while and putting it back into P, it can sit at 900-1000RPM about 20 seconds, but within 2 minutes will calm down to 750-800RPM in P. Totally normal. Don’t get hung up on high idle unless it always sits at 1000.
Idle speed for the 6.0L should be set as in the manual, which I posted 3 posts earlier.
You don’t want it lower, because when there is load, the speed will drop and there may not be enough coolant flow while you’re stuck in traffic and/or the alternator may not charge.
You don’t want it much higher because you don’t want to tax your torque converter and transmission when switching into gear and…because sooner to later the 36CU will have to perform the “infamous” adaptive fuel trim:
Yours truly has spent a large part of the past decade chasing smooth idle out of my 6.0L.
From my own experience, with a rebuilt AAV and new gaskets/vacuum hoses, once you set the idle speed correctly, you won’t have worry about it for some time.
Thanks Steve
that was the plan when I started changing all the gaskets and hoses + rebuilding the AAV
first test will be to remove the air supply to the AAV
I can’t see the injectors not being tight , as their gaskets have been changed too, and they’re blocked between the manifolds and air rails (no injector hoses as per the older V12)
I could still try and spray some carb cleaner around
the butterfly close properly : I checked before and after re installing them
all manifold nuts seem to be tight, but I’ll have another check
I hoped I could check the AAV by removing the top hose bend to manifold, but it’s too short to be moved out
only ways I can think of are :
taking the manifold out / raising it enough so the AAV hose pops out
take some coolant out and remove the AAV from the engine
not being very tempted by either solution, I went around the engine and tried unplugging vacuum hoses one at a time, and awaiting for idle rpm rise
all but one do so, so I hoped I’ve found a good suspect : this is the bigger one out of the rear of the right manifold, which goes to the firewall
I used a hand vacuum pump, and got light vacuum in the lie (-16PSI, according to the gauge)
20 minutes later, there’s less vacuum, buts still some (-13PSI), so doesn’t seem too bad
I even tried and nipped the manifold nuts a bit more, trying and compress the gasket, but this didn’t change the result
bad idle, and FF34 code coming back within a few minutes
I need to figure where are the O2 sensors connectors, in order to try Steve’s suggestion and disconnect them
any suggestion welcome
Mine are pretty easy to trace from the sensor upwards and gathered into a clip on the engine side of fender well. Probably wrapped in a heat insulation loom fabric also
The big one off the back of the manifold is the the vacuum to the 36CU in the boot.
No surprise you have a huge difference in the running condition - the MAP signal is lost and the ECU feeds the injectors at WOT.
The other one is the vacuum line to the Marelli ECU in the passenger (LHD) footwell.
Third IIRC is for the heater control valve and the last must be for the emissions control.
The connectors for the injectors are on each side, in the engine bay, down, very down. Look at the exhaust manifolds, somewhere in that area, probably zip-tied to something in that vicinity.
Nothing is easy on the v12 :-))
To test for vacuum and AAV - I’ve posted this many times before - remove the filter element on the B-bank. Toward the back of the airbox housing you’ll see a large hole 3/4-1" sized, where the intake hose going to the AAV connects.
Warm up the engine, then, with a solid plug (not rugs or nylon) cover that hole.
The engine will almost stall and the rmps will drop to unbelievably low 300 or so.
The beast will still idle and will be breathing very heavily. You will be able to hear where the air enters into the engine easily.
For example, major hissing will be coming off of the little filter that is at the end of the vent tube for the dizzy. Study for a moment where the line for the distributor vent scheme connects and will understand why.
I took the hard way, and loosened the manifold end plate, and raised the manifold, and could ‘just’ get the hose out, then screwed everything back to position
I took a measurement of the piston position when cold : about 70mm from the top of the AAV
I got the engine running until hot (by adding a hose to the AAV port in the manifold, and keeping it almost closed so the engine ran
then a took a measurement again of the piston position, which seems to have very limited move , at 64mm when hot, so only 6mm throw, which seems to short to get the pisont fully up
I reckon next move it to take the AAV off, and try and figiure out what went wrong
I have done this before, and mine only dropped to about 400-450rpm. I then plugged the vacuum to the PCV (Positive Crankcase Ventilation) valve and it dropped to 250-300rpm. So remember, your PCV is a ‘vacuum leak’ too.
BTW, the AAV’s on this car are notorious to not function correctly at this age. They are either stuck, or in most cases (like mine) are ‘tired’ and don’t close all the way. I sent mine to a forum member, Jonas, who rebuilds them.
Works like a charm, and then I could set correct idle adjustments knowing that the AAV is 100% functional.
