E38 idle tuning

[hymey]

THIS THREAD OUTLINES E38 IDLE TUNING AND ADJUSTMENTS. PLEASE READ THROUGH ALL FOR INFO IN DETAIL OR PLEASE SKIP TO POST 25 FOR A FASTER SIMPLIFIED VERSION




While the challenge has always lied in perfecting the VVE table I have found getting the perfect idle more challenging. My car has a 218 224 112 cam which is relatively small compared to some setups. It sounds good at idle but to be honest my old 308-LJ idled better with a crane 288 solid cam and 750DP Holley.

While you can get a e38 controlled engine idling well getting them idling very good is more challenging. I have been experimenting a lot getting a decent idle with no hunting, basically the engine idles like stock now with a deep note and I have pulled 10% fuel out as so much was passing through before.

Basically I zero out the airflow correction tables B1845 and B1843. Then use B1829 to adjust throttle percentage at idle. If airflow and TP is correct we dont need much correction. So increasing or decreasing g/s values in b1829 will adjust TP to where you need it for correct idle speed. During this time there will be timing correction taking place keep a close eye on it and use this to help verify if it has to little or to much timing.

You will find at this stage idle is dead smooth if it is not keep working at B1829 to get a decent idle.

B1845 is proportional correction and integral is 1843. Proportional changes are direct adjustments to airflow where integral is a sum of these adjustments. Basically short and long term corrections. I disable B1843 by leaving the tables zeroed out as I previously mentioned. I then build a new table with b1845, this will ensure a dead smooth idle. But one thing. I put in the value -2.00 to all the cells in this table and it consistently reduced TP by around 2.8%, this verifys how much TP it takes away, If you look at the factory table rpms less then commanded idle have negative corrections and rpms above commanded idle have positive correction. I first set mine up like this and it hunted badly. It is ass about. Negative numbers reduce TP so they must be added in the cells adjacent to rpms above commanded idle. I tested this myself and now it works correctly which solves the hunting problem. Once I got this far I zeroed out the under and over timing correction tables and used bidi controls to raise and lower timing to find a happy medium, then re-established the timing correction tables.

cheers

Joel