Have an 01 GT with approximately 10k miles on a new engine with a Z7 kit on it. Car has been driving fine for a year. Last week the car would not hold an idle and stalls. At idle the engine just cycles up and down and finally dies. Unplugged the IAC and the car would idle, but would then throw a P0507 code. Replaced IAC, no change. Replaced MAF, no change. Replaced PCV, no change. I'm assuming a vacuum leak but there is nothing obvious. Was driving the car without to much of an issue for about a week, but now, my speedo is haphazardly working, which, I'm assuming, is causing my transmission to not shift properly if at all! I basically have first gear, when the speedo begins to read, it shifts up, then the speed dies and it shifts back to first. Any assistance would be greatly appreciated!
