For those who are having Idle and Part-Throttle Surging
I figured I would post this to help hopefully one person that is having severe surging problems at idle and part throttle. I will post this in the Gen 3 area as well.
I have been playing with my OS allot lately and I made the switch between OS3 and OS5 The problem I ran into was that I started getting big time surging at idle.... My engine would start and then after 5-10 seconds would come down from a 1400 RPM start-up high idle and then would surge from around 600-800 low rpm, to about 1100-1300 high rpm, keep in mind my idle is set at 850.... I could not figure out wy neither as I changed nothing but the OS. After doing some logging I notice my surge would cause my timing to peg at 46 deg. WHY I DONT KNOW!!!! However this pointed me to a false assesment that it must be Idle airflow calculaions because more air at idle would ask for more timing. Anyways... After searching through base timing tables and base timing setting I ran across something.... In my engine overspeed table it was calling for Pos. timing!!!! So what was happening was when the engine would be above my set RPM at idle it would add timing compoundng the situation further untill it maxed at 46 deg. After changing the settings in that table to neg. numbers my surging was fixed entirely.... I checked my old tune with COS 3 and compared the engine overspeed table and my values in that table were neg. like they were supposed to be.
Long story short.... Somehow when making the switch or flashing my PCM my table was changed without me changing it. I am probably a once in a thousand scenario but I hope this helps someone that is having similar problems and cant seem to find the answer.
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Originally Posted by chevy052500hd
