Ford - Thunderbird :: 1996 - Shake Harder And Faster With Increased RPMs

I've got a problem with my '96 Tbird that's really stumping me. It started with a little shake when I gave the car gas. I don't know if it's related, but I ran over some debris on the highway at around 70mph. [No chance to avoid, unfortunately] That same day it felt like the car was missing, and throughout the week it got worse and worse. It would shake harder and faster with increased RPM's. By the end of the week, it was so bad I kept the car off the road.

I thought it was a bad misfire, so I changed the plugs, then the wires, then the EGR and EGR solenoid [from JY] and swapped a coilpack from my other car. It ended up being the harmonic balancer, it spun a 180, not a surprise on an 18 year old car. I've never had one go bad, so I didn't even think of that as a possibility with the way the car felt. [I've been working on cars for a long time.] It never threw a code once, so I had nothing to go by to begin with.

So over the weekend I swapped out the balancer, and buttoned everything up. Ran fine! No shake! But then I had gotten a new problem.

The idle started to get bad. Very bad. It would lope, lope then almost try to stall, especially when the fans kicked on or I put it into gear. Since this car is my daily driver, I had it at work while I started to undo the new stuff I put on it. I started with the just unpluging the battery for 3 hours. Didn't work. So I pulled the new plugs, reverted them back to the old ones. It didn't work. Leaving work that day I noticed if I pull the IAC connector, the idle smooths out some, but it doesn't stall. [Suspect, maybe?]

So I figured it was the EGR, or solenoid, so I changed them both out. Nothing worked, still was horrible. Frustrated I changed out the coil pack and wires. It's still horrible.

I don't drive the car now, it stalled out a few times in traffic on the way back before I swapped everything back out.

The icing on the cake is that it has not thrown a single code except for when I unplug the IAC. And the only code it throws is barking at me for doing so.

It really feels like a bad vacuum leak. I've run down every single line and there's nothing leaking or rotten. The IAC is in question, but the car was working perfectly fine for at least a year with no problems whatsoever. So how the IAC went bad right after changing everything and a new harmonic balancer is way beyond me.

I'm thinking too maybe I damaged the Crank Position Sensor when I installed the balancer, since it was a one piece unit with the pick-up gear. But, I was careful with it, used a puller installer, and there is appropriate distance between the sensor and gear. Also, I'm not sure, but I doubt the Crank Sensor going bad would effect idle. Any RPM above 1500 is smooth, and doesn't surge.