Glad you're feeling better. Lol I see some crazy posts, but never any with the problem you listed.
Anyway, it almost seems like the problem is temp related if it idles normal at start. As far as the vacuum leaks, it can be dangerous, but I use carb cleaner to check. If there is a leak, it sucks the carb cleaner in and the idle speed will change.
As far as the IAC, what happens if you disconnect it? Do the RPMs go really high? If they do, then it is working.
That leads me to the EGR. The egr on your vehicle should be vacuum operated. If it isn't holding vacuum, the RPMs can increase as the engine warms. To check it, you should do two things. First, confirm there is vacuum to it. Using a vacuum gauge, vacuum should be around 15. If that is the case, then you will need a vacuum pump to check if the EGR is holding vacuum. Most parts stores will lend you both the pump and the gauge. If you want to try it, let me know when and I'll try to make sure I'm online to help guide you. It really is simple to do.
One last thought. Double check all of the intake bolts and throttle body bolts to make sure they are tight. I just dealt with an idle issue similar to yours. After eliminating the things I mentioned to you, I found two bolts loose on the intake. I tightened them and the idle dropped to 800. Also, recheck to make sure none of the vacuum hoses are damaged or disconnected. Often times, the manufacturers will use a 90 degree turn in a hose. Over time, they always seem to leak there.
Sorry, this is the last thought. Since the check engine light is going on then off, try to get to a parts store to have the computer scanned when the light is on to see what code is showing up. Even if the light is off, there could be "Pending Codes".
Let me know.
Thursday, February 19th, 2015 AT 4:14 PM