Do you have a scanner? Good scanners will give you a misfire table by cylinder. Even if your getting P0300 random misfire its likely only one cylinder. The cylinder closest to the vacuum leak.
I have found that most misfires at idle are vacuum related!! (injector o-rings, vacuum fitting, boost bypass, egr tube, vacuum fitting on top of supercharger, TEE UNDER THE SUPERCHARGER SNOUT)
Most misfires under power or boost are spark related. (plugs, wires, coils, etc..)
So you now only have misfires at idle, so its vacuum. Have you replaced all the rubber ends on the vacuum lines? If you still have the stock ones there not great. If they weren't leaking they are as soon as you pull them off. Pinch them and you will see little cracks. There is also an EGR tube from EGR valve to intake manifold that can crack which is an instant leak. I never had much luck with spraying carb cleaner, I recently smoke checked my car and found the the Vacuum fitting on top of the supercharger was leaking.
I've had 7 SSEi's so over 10 years so far!
44,000 miles!!!!! Does it still have the stock black plastic lower intake gaskets? Change them and the plastic coolant elbows as soon as possible and you got a great dependable car!!!! Use aluminum elbows from dorman and aluminum LIM gaskets!
_________________ 02 SSEI, 1.94 Yella Terra,Gen5 , N*,2-1/4""Phenolic Intercooler, I SELL, Phenolic Intercoolers, Pulley Pullers, Throttle Bodies, Etc...!!
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