Fast idle on startup

[Jetskier77]

2017 Tahoe 65K miles, 5.3 engine. A few months ago, the truck started idling fast (1300rpm) at the first startup of the day. Outside temp does not seem to effect this behavior. It does this about 95% of the time and then it will be fine the rest of the day. Takes about 90 seconds for the idle to drop down to about 700/800rpm or so, where I can finally put it into drive safely. I'm pretty handy with older cars and have no trouble tracking down issues, but with all this computerized junk, I'm at a bit of a loss as to where to start. Air filter is new, I gave the engine a good inspection for loose wires/connections and I just completed a fuel system treatment which made the engine run a tad smoother, but the fast idle remains at first startup. Any ideas?

 

[Fless]

Has the throttle body been cleaned lately? Also after a cold soak overnight and before a cold start verify the outside air temp and intake air temp readings with a scanner; they should be very close.

 

[jaxscuby]

cold start..
with fuel injected vehicles..the ecu like to richen the air-fuel ratio from 14.7 to about 12.5 for a short period of time.
think of it as what the choke plate did to the airfuel mixture on carbureted motors.
and then the ecu will start to lean the air fuel ration from 12.5 back to 14.7..once the motor has started to
warm up.

clean you MAF sensor & replace your air cleaner.

 

[Fless]

cold start..
with fuel injected vehicles..the ecu like to richen the air-fuel ratio from 14.7 to about 12.5 for a short period of time.
think of it as what the choke plate did to the airfuel mixture on carbureted motors.
and then the ecu will start to lean the air fuel ration from 12.5 back to 14.7..once the motor has started to
warm up.

clean you MAF sensor & replace your air cleaner.

Wish the OP had come back and updated this.