interallen

Here's what happens, my TT warms up normal, then drop down to 800 rpm for the first 10 - 15 minutes of driving time. After that 15 min of driving, it jumps to 1000 - 1100 rpm and stays there! It even triggered the "check engine" light. My tech guy said the code pointed to the ISV (idle controller), and cleaning or replacement was suggested. I cleaned the idle controller but the problem remains. I pulled the power for ISV when it's hot, the Rev stays at 1000 rpm. But this accidently cleared the "check engine" light! haha Is there any other area I should look at, before I use $400 only for the part??? It's out of warranty just 1 month ago. Any comments appreciated.