Get the 70mm, and as far as idle issues, they are usually from not setting the TPS correctly, and its not really that big of an issue, I got mine off fine using a sears screw driver with a long bit. Just put some ass behind it and it will come right out. Make sure the TPS is set right about 1.0. Also, make sure to recheck it when the car is running, off, my cars tps said 1.00. When we started it it went to 1.07, so just double check it to be safe. Good luck.