Bf Xr6T Rough Idle: Help Please!

[pggoesbang]

Hi All,

At my wits end and need some help! My XR6T (2007) is drinking fuel and running rough and engine light on. Checked out the obd2 and had no voltage on O2 sensor 1. Pulled it out and its covered in carbon, replaced it and has helped as car is now at least back in closed loop mode. No engine light now.

However Long term fuel trim is up at + 25 on idle so it is still lean (Or thinks ts lean) at idle and as such is running rough. When I take it up to 3000 rpm etc the fuel trims come back down and look to be fine. So im thinking its a vac leak and have spent the morning spraying carb cleaner over everything, and have been blowing cig smoke into vac hoses with a glove over the throttle body to try and find the leak. No luck! cant find the dam leak anywhere.

Wondering if there is another way that I can assure myself that the Vac is good. I dont want to cancel it out just because I havnt been able to locate it. How can I assure myself that the vac is fine?

In the event that it isnt a vac leak im Wondering what else would drive the fuel trim to do this? from What I understand a bad MAF would do the opposite so I'm cancelling that out. I have had my bolts on turbo manifold loose previously so am about to go see if they need nipping up? Would Exhaust leek drive same behaviour on the fuel trim ?

I have also changed plugs, and coils about a yr ago.

Appreciate any help!

cheers Guys.

Pete

[frankieh]

An exhaust leak can certainly cause lean out at idle. Get someone to cover the exhaust with something while you listen for puffing up between the cat and the engine... Also, did you reset your KAM data after you replaced the o2?

I had a similar issue with my BA (similar, but unrelated I expect, just of possible interest), rough low idle no matter what I did.... replaced the intake manifold gasket, replaced all the plastic fittings for brass and changed the PCV valve, then got a BF throttle body and TPS and swapped that in.. then pumped the engine full of smoke to see if I'd missed anything.. no smoke. (I used a paint tin with two holes in the lid, one from the compressor and one clear hose up to the booster hose... worked well.. had half a dozen red hot BBQ brisqetts soaking in cooking oil inside the tin to provide the smoke.. but found no leaks. Then I picked up a SS inductions larger Throttle body and put that on.. still didn't help the idle. I also changed to weaponX 80,000 volt coils and got a voltage booster (because the factory +'ve rail isn't much chop) and brisk silver LGS plugs (I run injected LPG most of the time).... all of that helped a little, but it still idled under 600rpm and sounded rough..

In the end, by process of elimination I was left with only the accelerator pedal as everything else had been changed.. turns out I started at the wrong end of the system.. the slide sensor in my accelerator pedal was naff and just wiggling it results in a different rpm idle each time.. so I binned it and put one I picked up in and it has helped quite a bit.. the rest I will do by tune... Never showed up in codes.... so as far as the PCM was concerned, it was getting a signal.. so it was fine.. it was just not the right signal, at least not at idle. I have a wideband and it never leaned out too much so it was just annoying not dangerous.... I spent a fair amount of money getting rid of the problem, but it was all stuff that is beneficial to my power goals anyway, so it's all good. I now get to run high boost while running big gapped LPG three pronged silver spark plugs.. great for smoothness and economy, and with 80k volt coils they don't blow out under boost anymore. win win!