Update: problem solved!
This issue started about a few weeks after I bunged on some Tickford TE50 heads and an intake insulating spacer. I'd already fitted an SS CAI.
It was pretty obvious the thing was running lean at idle and as a he thread shows we chased a lot of things to try to find the cause.
It had to be a vacuum leak, that is air entering the intake without being registered by the
MAF sensor.
Then it hit me, what if there's now more air coming through the
MAF and the engine tune is now out of whack?
I went for a run with the OBD2 connected and Forscan running, I gave it the boot a few times to datalog the MAG flow and
MAF voltage.
I came home and wrote it out in a table, then compared it to the
MAF transfer in the
ECU's tune (using a Moates Quarterhorse and Tunerpro...
Bugger me it was a reasonable way out. The engine is getting more air than the tune expects.
I thought perhaps the
ECU would learn from the
MAF voltage and adjust itself so the car idled better, but as we know the short term fuel trims chased the lean reading from the O2 sensors all over the place.
So I adjusted the time's
MAF transfer table to match the
MAF data I had logged. Problem solved!!!
There's still a bit of tweaking to do but the mad idle hunt has gone.
Thanks for your help and advice blokes. What a top lesson this has been!
Here's the before and after
MAF tables...
Before
After
