Engine Weird cold start idle


Active Member
Feb 6, 2020
So my 2017 manual GT is bone stock other than an X pipe in place of the stock resonator and some MBPR mufflers. It has 78K miles on it. Ever since I bought it about a month ago it’s had a weird cold idle issue where upon starting it in the morning or after a long day at work, it’ll idle up high like it’s supposed to then a few seconds later drop down to like 1000 then back up to 1500 and bounce a few times but not in an erratic way. Then after about 30-45 seconds it’ll settle into its high idle and slowly settle down as it warms up.

In a lot of other coyote mustang cold start videos they don’t seem to do it. They just go right to their high idle and slowly settle down like they should. I’ll get a video of it in the morning if I remember but here is a another thread I found on another forum that listed exactly what I’m describing

If anyone has any suggestions or pointers it would be greatly appreciated. I’d like to have the car function exactly as it should from the factory as it’s my new daily.
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