High Idle

Hey guys back again with another issue.

2000 v8 ls. starts fine in the morning, however recently it has begun to high idle for long after the normal high idle period. this is what happens generally:
1)starts fine, idles around 1200 then slowly down to 800
2)stays at 800, i take off out the drive way
3)sit at the stop sign and notice it wants to take off like a bat outa hell
4)throw it in neutral and the idle is between 1500 and 1800 (not normally btw)
5)after a few minutes back to normal

seems like once the car is completely warmed up there is no issue. it just happens the first 5 minutes im driving, and has only recently begun to happen this spring.

any ideas?

thx

Is the idle rough at all either when idling at 800 or 12-1500 rpm?

-Rod

Is the idle rough at all either when idling at 800 or 12-1500 rpm?

-Rod

smooth as butter. i havent detected any type of misfire and no warnings have gone off.

Check the throttle body assembly where the mechanical throttle cables connect (one from the gas pedal and one from the cruise control). There are some plastic bushings that are known to fail. I suspect that it might not really be an idle problem but instead maybe your throttle is sticking open a little bit.
If you can look at the throttle while the engine is revving too high, see if you can push the throttle closed and resolve it.

Interesting. A few years ago the throttle cord was replaced, under warranty, because it broke. The dealer was like, this is a first...

I'll check it out but it almost like the car is going through the "warm up" twice which leads me to think of a faulty sensor.

I wonder if maybe you have an Engine Coolant Temperature (ECT) sensor that is telling the PCM that it is colder than it really is. If it wasn't idling smoothly I'd suspect a vacuum leak or misfire that occurs after the engine gets up to temp (something cracked that expacts as it heats). I suppose that could still be the issue and the IAC is speeding the engine to keep it from stalling.

-Rod

If I run by Autozone tonight and run the diags is there an ECT error number I shouldbe looking for? How hard is that to replace.

There are codes that point to ECT, and there are probably more then one, but I'm not going to scan the long list to attempt to pull out codes for the ECT. If there are stored diagnostic codes, get the code number (in the forum P0123) and post back. Autozone will give you their interpretation of the code and what needs to be replaced to fix it. Sometimes they are correct, other times their suggestions are not accurate.

-Rod