Ford Repair: 99 Mustang GT idle & performance, hypertech programmer iii, rear gears

Question
Hi Steve.
I have a 99 Mustang GT, automatic with 14k miles. Complete Magnaflow system, Steeda underdrives & timing adjuster, full densecharger CAI, TB spacer, intake spacer, and last night installed a FRPP 90mm MAF. Before & after these mods I have a slight idle flucuation (550-650), but it otherwise runs great. Should I mess with smoothing out the idle & what should I look at to do so? Seems like a better throttle response since installing the 90mm MAF - Am I really gaining anything with the 90mm MAF with my present setup? I also just got a Hypertech Programmer III and am yet to plug it in and do some mild performance settings. Should I put the Steeda timing adjuster back to the stock 10 degree setting before using the programmer? And finally, will the cost benefit be worth me doing a rear gear upgrade, and if so 3.73 or 4.10? Many thanks!. Joe  

Answer
Joe-

  I wouldn't worry much if the fluctuation is only 100rpm.  It's still a pretty decent idle speed.  As for the gain of a 90mm MAF, that's a matter of debate.  It could help but it's big enough that it could actually slow air down and hurt performance.  I'd leave it on there either way, especially if you plan more mods in the future.  As for the programmer, yes, I would set the Steeda adjuster back to the stock setting.  The Hypertech unit will adjust the stock timing curves and if left in a "performance" tune, the adjuster could do damage by giving too much timing.  Rear gears are always a good bet.  I've found that most people really like the 3.73s on an automatic car unless they like to hit the drag strip a lot and then they prefer 4.10s.  It won't give you any actual power, but it's one hell of a difference by the seat of your pants.  Hope this helps.

Steve