Hi guys
I'm battling with a tricky issue on my R56 (2008) MCS. It's blowing a ton of black exhaust smoke (it's not drive-able) from idle. Takes a minute or two for it to start happening from turning on the ignition, but when it does, its like a diesel tractor. Clearly running a very rich AFR.

Bit of history about the issues I've had (it's a bit of a long one):
The car is running a Manic Mini stage 3 map, 2.5" turbo back exhaust/high-flow cat, JMTC super K03 turbo, pod-filter air intake, and an ebay intercooler (forge copy). Most recent modification is the intercooler and colder NGK IILKR8E6 plugs. Prior to changing the plugs the car was running fine, but I'd never pushed it to the limit. I put the NGK's in to prepare it for the dyno power-run, as I didn't want issues with pre-ignition, however they caused a rough idle (but no smoke), so didn't think too much of it.
On dyno day, it survived on the most aggressive ECU map, but a I had a few runs left I started changing the maps with the SPS switch and combinations of sport mode off/on, just to see what the difference was. On the last run (medium ECU setting but sport mode off), mid-pull we got a boost-cut and I noticed a small puff of smoke coming from the front grill. ECU showed a "super knock" code. After that, it was not running well at all and not making boost (but no smoke at this stage). Visual inspection didn't indicate anything obvious, so they kept the car for a few days to inspect it. They came back with a diagnosis of low compression in 2x cylinders and turbo failure. Great. Only at this point I noticed it was showing the excessive smoking issue. We put the stock spark plugs back in but it didn't help much.

So, 1 month later, I've just had the engine *completely* rebuilt, and a new turbo charger fitted (again from JMTC). I was scheduled to pick it up the other day when the garage just called me up and said they've there's still a load of black smoke pouring out of the exhaust and rough idle. Disaster. It's going to an independent tuner to examine the state of the ECU map, but I've not heard anyone have any issues with the Manic tunes before.
Assuming the tune is still OK (I won't know until next week), I'm now considering the possibility that the cheap intercooler could have cracked under the pressure of the dyno run, and is causing a boost leak. Or maybe a faulty O2 sensor somewhere. But would a leaking intercooler really cause such a rich AFR, even at idle?

 

in general, if you have a leak any where after the MAF, you would get a "un-metered air" code.

the smoke could be the burning from the first failure. did the shop check compression and leak down test? what was the extent of the "rebuild" of the motor?

where you located?

 

Engine rebuild was forged pistons, water-pump, oil pump, fuel pump, timing chain, all the usual stuff. Valves were refurbished, stem seals replaced, head skimmed. I'm in Australia, so we don't have the MAF sensor on the air intake. The ECU should be referring to static MAP values that were defined in the Manic tune. I've don't know if a leak down test has been performed since the rebuild (I assumed the workshop did this to verify their work) but I had one prior to the rebuild and I was low on two cylinders (about 110 and 120, whereas the healthy two were about 150). It's not burning oil smoke, its definitely more grey/back, indicating rich fuel mix.

 

Check fuel trims on scanner! Also, look at the temp sensor reading. If it reads extreme negative.... BINGO!!!! The computer thinks its in antarctica and will kill it with fuel. Outside chance an injector is hung wide open.

 

So, turns out the black smoke pouring out was caused by my recently installed JMTC super k03 turbo shitting itself (I advise anyone considering this "upgrade" to avoid the refurbished turbos from those guys). Refurbished = save a bit now, pay double later. A second turbo from JMTC fixed that. Car is now very derivable and the idle issue is nothing like it was when the turbo failed, but it has never *completely* settled down to what I'd epxect. I changed the plugs, ignition coils, the vanos solenoid (got an error code for that), and it seemed to go away for a week or so, but now has come back. The RPMs only seems to bounce around/surge at idle, particularly bad in neutral. As its an auto it has caused some hairy moments where the car has lurched forward when my foot hasn't been hard on the brake.
Struggling to get to the bottom of this one, even my local mechanic isn't sure. AFR's now seem reasonable between 14.4 and 14.9, fuel rail pressure around 700psi at idle, LTFT is reporting 0.0% , STFT varies between -2.3 and +1%. Most of that looks good to me (unless I'm wrong), so cannot work out for the life of me what is causing this idle surge. Disconnected the turbo charge pipe to isolate the intercooler and turbo, but still it wobbles in neutral.