This problem is on a 1998 Z28 A4 with a 230/230 cam, ported heads, and LT headers.
The lean condition only exists when on the SD tune. With the MAF I do not have this problem.
On cold starts my AFR will be in the 16 – 18:1 range for 5 to 10 min even though the OLAF table has an AFR of 13.3:1 at the idle RPM/MAP. With the scan tool I have confirmed a commanded AFR of 13.3 but my WB shows very lean and the car idles like it is very lean.
As an experiment I richened up the AFR in the OLAF table to 11.0x at 20c and tapering it up to 14.63 at 70c. This corrected the cold start lean problem. Commanding an AFR of 11.2:1 netted a real AFR of 13.2:1. As the car warmed up the difference between the commanded and actual AFR lessened. However as soon as the ECT hit 70c the AFR went lean at 16.x:1 at idle MAP. At driving RPM/MAP the AFR was 14.7:1. After about 5 min of driving the AFR at idle went back to the commanded 14.63:1
There seems to be evidence that there is another table or parameter that is affecting the AFR at idle (on the 98s) for a period of time just after startup. Every restart is going lean if the car has been sitting for 30min or more. If I just turn the car off and restart it within a few min the lean condition is not there.
Other possibilities:
I thought about how I had lowered the IAC effective area table (drilled TB) and thought that maybe there was additional air coming in the IAC/TB hole that the PCM was not aware of and therefore not compensating for. As an experiment I changed the table from 4 positions down from stock to 3 positions down from stock and flashed the PCM. On the startup the AFR went lean at 16 – 17:1. My IAC correction is only off by -.71.
Maybe an idle airflow table being off might cause my lean problem and the lean time on restarts is the time it takes the PCM to learn out the bad values. I might need to put the IAC effective area table back to stock or lower it 6 positions from stock and see what happens.
As I thought more about it I remembered that I had cut my VE while cranking table by 40%. I loaded the stock table back in and flashed the PCM. When I started the car the idle AFR went lean to 17-18:1 so this did not solve the problem
Any thoughts or suggestions?
Thanks
John