Quote Originally Posted by Roadknee View Post
The problem you're describing is not the norm for the 7427 ECM and TBI on a stock Vortec long block. The surging is caused by the O2 sensor swings on deceleration. I wonder if you have a very small exhaust leak (bad gasket, cracked weld in header or exhaust system, etc.) where fresh air is being pulled into the exhaust on deceleration only. The O2 sensor would see this as lean and the ECM would overcompensate until it swings rich, then overcompensate back to lean an on and on...
You sir are good, I looked and sure enough a nut has worked its way off the collector on the side that the NB is on.