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I have had these codes for a few years intermittently, and I clear them; they stay gone, then come back eventually. The car always seems to run fine. When its hotter outside its a little rougher at idle, but I suspect that is the tune. I have only driven less than 8k miles on my Cutlass since I swapped the L96 in in 2012. I have checked for vacuum leaks with both carb cleaner spraying near all connections (especially down near the intake manifold w/no change. Yesterday I made one of the $15 smoke machines off youtube, and I had no smoke in the engine proper; eventually I could see some that slipped thru the throttle body and traveled all the way up to my K&N filter and was seeping out there. I think that is ok. Last summer I went ahead and replaced the Corvette filter/regulator just to be sure it wasn't the issue, and that didn't change anything. Before I cleared the code today, I took pictures of the freeze frame data from my scan tool and the code set at idle. See attached pics. Any thoughts as to next steps? If it is only an idle issue, is it really of any concern other than just needing to clear the codes periodically? Also, I have not yet cleaned the throttle body (cleaned the MAF today). Its DBW; any issues forcing the throttle body open to clean it with DBW?
Thanks for any input you have.
Last edited by Goldhawg; Apr 22, 2019 at 10:30 AM.
I see your long term fuel trims are almost maxed out at 23 percent. Check your fuel pressure at the rail to ensure you have 58 lbs. When I had this problem it was traced to the wrong injectors programmed into the tune. Ensure your injectors and tune match.
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? on P0171 and P0174 codes 
