I've owned my 98 lsc since May 2000 w/20,000 miles. Currently 112,000 miles. This past week when first starting, the fast idle jumps to 2,000 rpm for 5-6 seconds before it drops down to 1,500 for 3-4 seconds, back to 2,000 for a couple more seconds, then to 1,000, then 800. I looked for cracked...