High Idle on Startup After Timing Belt Replacement

[oldman17]

I recently did the timing belt on my 2008 LS sedan. While I was at it, and since the airbox was out, I cleaned the throttle body (not by removing it, but just by opening the butterfly valve, spraying the cleaner in there and wiping with a lint free rag). I did the idle learn procedure after getting everything back together.
Before the timing job, when starting the car it would idle up to about 1200 RPM for 2-3 seconds and then come down to normal idle (750 RPM). For the first week after working the timing belt, this was still the case.
About a week ago however, whenever I start the car (cold or hot), the idle surges up to ~2000 RPM for 10-15 seconds and then comes back down to 750 RPM. If I tap the gas or pump the clutch and shift through the gears it seems to bring it down quicker.
I would think this can't be good (at least when the engine is cold) since the oil is cold and more viscous, and not lubricating the piston rings/cylinders all that much while at this high idle.
Anyone have any ideas on this one?

[ontarian_frog]

RPM is controlled by the ECU. It is normal behavior unless you have a vacuum leak.

[oldman17]

ontarian_frog,
Thanks for the reply. Do you have a good vacuum hose layout? I am thinking of going that route. I would say this is definitely not normal as it is a noticebly different idle pattern than before doing the timing job.

[ontarian_frog]

I do not have any diagrams, sorry. The vacuum leak would have to be between the engine and the throttle body. Did you disconnect or break any hoses when you cleaned the TB? Usually, if the rpm go back down to 750-850 rpm, there is nothing wrong.

The rpm when cold, are controlled by the IAC that lets air bypass the TB. If it was obstructed and you cleaned it, the rpm would also be higher.

[oldman17]

The only hose that was disconnected were the ait intake from the throttle body.