Ford - Thunderbird :: 1985 Turbo Coupe Dies When Coasting In Neutral

This problem has plagued my '85 Tbird Turbo Coupe for about a month. When I put my car in neutral while moving, the RPMs fall significantly below idle and then the engine usually catches itself and after about 5-10 seconds idles normally. If I do this at high speed (say 40 mph +), the RPMs fall to the point where the engine stalls and dies. If I do it at 25-40 mph, it will go down about 200-500 RPMs and then catch itself. If I do it at 15-20 mph, it will be just barely noticeable, and anything slower than that I can't notice it. It will also do this to some extent when I'm stopped if I rev the engine up really high and let it off, but it is far less noticeable. This car has had extensive work done to it in the past 6 months.

Most recently, I had the fuel injectors replaced, throttle body cleaned, IAC valve cleaned, and the vehicle searched for vacuum leaks. (most of that in search of the solution to this problem as well as to improve the general performance of the vehicle. A week before that, I also had a new fuel tank, fuel pump, and fuel filter installed. I've got a very small leak on the back of my muffler, no cat, and no other exhaust leaks I can find. I am getting a lot of black carbon out of the exhaust, but I have been running some fuel system cleaner through it. Also, the car sat for like 8 years before I got it, and the original cat became clogged and really gunked stuff up. I had all of the upper engine gaskets replaced, as much as we could get to cleaned internally, and the cat cut off at that point. Timing is very close to 10btdc. Could be 9.5, but just about right there. I double checked, no vacuum leaks that I could find with a can of carb cleaner. I tried checking for codes, but it's not even throwing me a confirmation code or anything, which is odd. But, my connector was pretty gummed up (I did clean it as good as I could) and just about anything wiring is suspect. I used two engine code readers that had previously been used on the car. Other than this, the car has plenty of power and runs fine down the road.

Here's the master list of what I've replaced in the past 6mo:

FUEL SYSTEM Fuel Pump (twice) Fuel Pressure Regulator Fuel Tank Fuel Injectors
ASSORTED FILTERS Fuel Filter (twice) Air Filter Oil Filter (several times) Oil Filler Cap PCV Valve
HOSES/COOLANT SYSTEM Nearly every Vacuum Hose Every Coolant Hose Heater Core (twice)
SENSORS AND COMPUTER STUFF Engine Control Module (ECM) Vane Air Meter (VAM) Idle Air Control Valve (IAC) Oxygen Sensor
STARTING SYSTEM/ELECTRIC/Misc. Spark Plugs and Wires (Motorcraft) Starter Solenoid Coil Pack Distributor
TFI Module Distributor Cap and Rotor Battery Timing Belt
EEC Relay Ignition Switch Tires Front Brakes Brake Master Cylinder (had previously been damaged) Front tie-bars Every gasket from the head up.