bhamg

"Stuck lean" signals a significantly lean condition that cannot be corrected by the ECU. If you didn't see these codes before they could well have been generated by the OBDII self-test cycle that happens probably every few thousand miles. The ECU induces both rich and lean conditions and measures whether minimum or maximum values are exceeded. My guess is that you are therefore running not just lean but very lean to be "stuck." (I've been "stuck rich" before.) Therefore there may well be more than just a slight air leak going on. Problematic as the primary O2 sensors are with this this engine, replacing them is a no-brainer IMO.

Celicasaur

SO after what feels like an eternity of having my car off road and not used (I was working on my other cars and needed to focus on those etc) i finally got the car working as normal again today.

I bought a used intake manifold from Germany which supposedly came out from a 2012 C63. I already had a fresh set of gaskets n bolts waiting (one of which snapped....second time it's happened to me!) so it was fairly straightforward to fit to the motor. The car runs....as it should, so I guess that was the solution to my issue.

Still doesn't make sense to me if the old manifold was deemed to be true from the engineering shop and it passed a smoke test, but there you go....

If I have time next week, I'll attempt to fit my 82mm throttle bodies in and update the TB thread if I manage to make any progress.

BerBer63

Did you new intake come with new hosing in the front as well or you used the existing pieces?

Savage-wp

Glad to hear you got it sorted. Have you I inspected the old intake manifold for hairline cracks.

BLKROKT

Great news

Celicasaur

It came with the bendy rubber that goes around the PCV and the long wiggly hardline (along with the t-piece rubber pipe that connects into the black airbox nipple).

TBH I've looked over the old manifold countless times and even smoked the hell out of it, so presumably anything big enough to leak air into it, would emit smoke from out of it, but no dice. It's weird man. I'm just going to salvage my throttle bodies out of it now and then chop it apart for a side project that will probably never materialise

bhamg

Yup, but good to hear you've solved the problem. My guess is this motor consumes maybe 500CFM of air @ 5kRPM so it's difficult to imagine hairline cracks making any difference at all. GL with the TB's.

mr747

Congrats mate

Celicasaur

I guess we'll find out towards the end of the week. It's either the throttle bodies or a crack that just can't be seen by the eye. Also FWIW I could barely get the car to go above 3000rpm and the vacuum leak was evident at idle from start up.

I tell you what though, the additional bodge-sealing on my airboxes (I'm guessing particularly at the back behind the MAFs) seems to have helped to make the drivability a lot smoother and responsive at light throttle inputs