Idle is hunting, Lean LTFT

[Wardie]

I have a 2004 330i E46, I recently had my rear main replaced. Upon getting my car back I started to feel the idle hunting when warmed up. My first question is there anything he could have messed with around the transmission to cause a lean condition?

Ive also replaced the thermostat, fuel filter (Which had a broken vac line), and cleaned out the ICV and MAF. Checked the DISA, still holding vacuum.

When I changed the fuel filter I had the check gas cap light come on for a few miles, but went away. Figure its because its a fresh filter.

Ive done a smoke test on the car and had a very small vac leak around the ccv but I dont think is big enough to cause -16% LTFT. I also think that leak has been there for awhile.

Unplugged each coil one at a time to hear for a change, they all bogged down figuring they are all ok.

Im getting a air rushing noise every time it hunts around the DISA valve or from under. Ive checked everything around there for cracks and leaks and everything checks out.

Ive been banging my head against this for the last 48 hours.

Fuses?
Relays?
Air in coolant maybe? (isnt overheating)
Gas Cap?

EDIT: I have zero codes.

[danewilson77]

We're these conditions present prior to the rear main being replaced? If the answer is No, take it back to the mechanic who performed the rear main seal repair.

Sent from my Samsung Galaxy S8+

[Wardie]

It always had alittle bit of a idle issue, nothing this extreme though. Going lean is new, I replaced a bunch of stuff when I got it home so its hard to tell. I had a family friend do the rear main, I asked him about it and said it ran fine after he test drove it. So, not really sure who to believe I dont mind doing the work and figuring it out. Just need alittle bit of advice where to start without buying parts and start hucking them into the car.

[BCS_ZHP]

Two ideas:

Open your gas cap, look at the rubber o-ring. If it's cracked (or missing), replace the gas cap immediately. It o-ring is intact, spray it with silicone spray and allow the silicone to settle in, hopefully it'll plump up the o-ring somewhat.

On the small leak around the intake boots/DISA/ICV, when the idle stumble starts, spray around that area with carburetor cleaner. The liquid of the carb spray will temporarily seal up the vacuum leak, you'll hear the idle increase. Keep doing this until you can pinpoint the exact spot of the vacuum leak, then fix it.

[Wardie]

Ill check that out on the gas cap.

Intake boots are brand new and checked for cracks, all good. The grommet for the ICV is brand new too. Little hesitant about the carb cleaner around the alternator, Ive had a mechanic spray it around it before and it went up in flames pretty good.

Is there anything below the CCV Oil Separator that could be losing vacuum?

[BCS_ZHP]

Sometimes, since you can't see 360 around it, the boots are not completely seated as you might think. On the spray, use anything, brake cleaner, even water. If there's a vacuum leak the leak is going to suck the liquid into the small gap and temporarily seal it for a couple of milliseconds. I suggested carb cleaner because it acts like ether and there is an immediate slight increase in the idle as it's receiving a richer fuel mixture, it's a dead give away.

[Wardie]

I reinstalled those boots probably 5 times in the last 24 hours. Ill have to grab some carb cleaner and give it a go. I just have a real hard time believing that a small vac leak would cause -16% LTFT. What do I know though :headbang

[BCS_ZHP]

When you replaced the intake boots, did you replace the plastic "F" connector and the small vacuum line attached to it? If not, my guess is your leak is there. The dealer sells that "F" connector for about $3-5 and a 4-6" piece of vacuum line is like a buck.

[Wardie]

I never took off the F connection, I replaced that smaller vac line that runs down to the fuel filter aswell, Well just the ends of that line.
The only things that have changed since it last ran fine was...
-Thermostat / Bleed
-Fuel filter
-Cleaned MAF, ICV, DISA
-Rear Main
-Brake Rebuild / Bleed


Figure I can check that gas cap and just double check all the spark plugs for fouling.

[Wardie]

Looking at it the fuel trims while driving I noticed that while driving I hover in the -.2% to 3% LTFT on both banks. However when I sit at a light or stop sign "LT FTRM1" goes to about 3-4% and "LT FTRM2" goes to about 15-22%.

Bare with me but if I understand this correctly my o2 is picking up that bank 2 LTFT is rich?

Would this be spark plugs / injectors?

[Wardie]

Turned the ac on while test driving and every time I come to a stop the car dies.

This is getting frustrating. Going to check spark plugs today.

EDIT: Checked spark plugs, all good.

[BCS_ZHP]

I never took off the F connection, I replaced that smaller vac line that runs down to the fuel filter aswell, Well just the ends of that line.

There is no way to "replace the upper intake boot" without removing/replacing the F connector. So if you did not replace your upper and lower intake boots while checking the DISA and ICV, look around the intake boots. They may look okay to the naked eye but need to be replaced every 4-5 years no matter what the mileage is.

[Wardie]

Oh, I mean when I took everything off to clean the ICV and DISA I didnt remove the F connection. Im unsure if I replaced it when I replaced the boots.

Going to go rent a fuel pressure gauge and go from there. Theres a guy parting a ZHP down the road surprisingly and was gonna go talk him into letting me test his DISA and MAF in my car.

[Wardie]

Rented a fuel pressure gauge from Oreilly and low and behold, theres no fitting for the E46....

I have my suspicions that its not fuel pressure related because the car drives fine. Whatever it is seems to be only effecting idle.

[ZHPizza]

There is a Schrader valve on the fuel rail that I just hooked a regular screw on pressure gauge to to monitor the fuel pressure leaking down with the pump primed (key in on position).

And as far as vacuum leaks -- I have no idea if it would cause the idling issues that you're having, but I think you should check the rear main seal. In my mind at least, you could be pulling air through there, through the crankcase, through the ccv and into the intake. Effectively being a long routed vacuum leak.

[Wardie]

Yeah the fuel pressure gauge from oreillys doesn't fit mine for some reason. Harbor freight has one for 20 that might work.

I hope it's not the rear main again. The guy who did it is a master mechanic haha. There's always a possibility I guess. Might have it taken to a shop just to figure it out. Quoted me 188 to find it.

Where is the hose for the sap? I think I read it went on the back side of the motor along the firewall?

[Wardie]

https://youtu.be/x_NeQbJqdN8

I'm sure this won't help much this is the sound I'm hearing around center or rear of the manifold.

[Wardie]

Smoked it out again, Saw smoke coming from the center back valve cover bolt. It mustve backed out, tightened it and then the CCV hose to the valve cover to the separator came a little loose. Bam presto, problem solved. At least for now! Thanks all for the help.