 1988 Mustang 5.0 timing issue / popping spitting
Ok, I have a weird one (for me anyway). First, the car: 1988 GT convertible, 5 speed. 121k miles. I do not know the history of the car/engine, however it appears to be stock, mostly original!
Now, for the problem: I do have an idle problem, and also an ignition problem. First the idle problem: idles between 1100 and 1500 rpms. i cleaned the IAC, checked the TPS, and reset the idle settings by disconnecting the battery/etc. No effect... so I unplugged the IAC. Idles much lower now, sometimes around 800 but sometimes as high as 1100.
BUT... under load below 2500 rpms, sometimes it hesitates and pops... can't tell if it's popping back through the intake or out the exhaust. It does this after it has warmed up. SOMETIMES it doesn't do it and runs fine, but most of the time lately it does this (it's getting worse). Engine feels like it's hestating a bit until it gets close to 3700 or so, then clears up.... so much in fact that it instantly smokes the tires in 1st if the throttle is 3/4 to full WOT. (car has 3.08 'airplane' rear end gears)
Today I replaced the distributor cap and button, as the contacts inside the cap were a bit corroded. No change.
So, tonight I was at the folks' and we checked the timing. Or tried to. I pulled the the advance terminator plug and we hooked up to #1, and couldn't see the timing mark around the tang near the harmonic balancer towards the passenger side of the engine. We thought it was due to surface rust on the HB, so we found the mark and marked it with crayon.
Still couldn't see the mark. Got to looking around, and found it... 180 degrees nearabouts (hard to tell for sure) from where it should be. Soo.... how can this be? The engine has a VERY slight vibration, but not enough to make me think the HB has spun. Aren't the HB's keyed on these engines?
Anybody got a clue what's going on with the HB? And what else should I be looking for that's causing this popping problem? | 
