Idle jump at time of turning off
 

Got my idle sitting pretty soilid, after some cleaning of the ISV, the air throttle screw, by-pass tube in throttle body and body plate.
I add a second o-ring on idle screw normal or not? it did give me the ability to make a better ajustment.
The only thing that I noticed is after fully warm, when I turn off key after letting idle for 20 secconds, that the tack jumps up to 1100 rpm. Could it be that less fuel at shut down gives me the rpm jump?
Haven't tested CO, my emission test from last August was 15.58 limit 30.00 miles per gram on CO. No where near the 3.5% unless I should move the decimel over one point to read this right, and then it seem that it would be lean at 1.55.
Any thoughts on the idle jump?
Thanks

What model/motor ?

87/911/targa/177,000mi 3.2l

That means the gas is shutting off faster then the spark by milliseconds, sort of common the fuel pumps only run when the car is being fired up or running .

Have you ever gone to the factory five racing shop in Wareham ?
They build some great cars there.

I know the town, were is factory five race shop? any names?

It's right near the exit off of 25 behind the gas station is some warehouses they build the cobra daytona's and cobra's.The owners daily driver is a porsche ( red 944 turbo ). You should stop in and try out there cars they are very friendly. Google the name factory five racing and it will show you everything.

Checked it out I'll stop by some Sat.
Thanks