Car Dies In Neutral When Coasting

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Car Dies In Neutral When Coasting

March 15, 2011, 12:51:18 PM

This problem has plagued my '85 Tbird TC for about a month, and I'm running out of ideas to fix it...

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 ler, 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.

Thanks for the help!

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

Car Dies In Neutral When Coasting

Reply #1 – March 15, 2011, 09:25:09 PM

Does it act up under any other cirspoogestances? If not, stop putting your car in neutral :)

Car Dies In Neutral When Coasting

Reply #2 – March 15, 2011, 09:40:23 PM

Quote from: CoogarXR;355473

Does it act up under any other cirspoogestances? If not, stop putting your car in neutral :)

lol.

Car Dies In Neutral When Coasting

Reply #3 – March 16, 2011, 10:06:24 AM

Lol, yes, it has started to act up quite a bit. For example, after driving on the highway and then coming into the city where I have a stop lights, I have to sit at the stoplight revving the engine to keep the car running. If it weren't for that, yeah, I'd just skip neutral!

Car Dies In Neutral When Coasting

Reply #4 – March 16, 2011, 11:39:51 AM

I just pulled the IAC Valve and cleaned it out with some sensor-safe cleaner.

Checked the voltage at the TPS .96. I ran through the full motion of the throttle and it was very even throughout.

So here's where I'm at...

Timing is very very close to 10btdc
TPS reading .96, shows a steady increase and decrease through range

Idles at almost exactly 1000 RPMs when first started, or if you let it sit for a while.

IAC valve cleaned
Throttle Body Cleaned
Entirely new fuel system just about everywhere (pump, filter, injectors, tank, and as of a few months ago, pressure regulator.)

I can't find any vacuum leaks, and neither can a shop.

Car Dies In Neutral When Coasting

Reply #5 – March 16, 2011, 06:32:50 PM

Codes ?

Car Dies In Neutral When Coasting

Reply #6 – March 16, 2011, 08:43:53 PM

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 and it has always worked in the past.

I'm not seeing any wiring issues offhand with a quick glance, just saying it's a possibility on this car. So...either it's related, or it's unrelated. I plan on checking the VREF signal a couple places next, as I've had a faulty sensor pull down the computer before (although in that case, the car wouldn't run at all).

Car Dies In Neutral When Coasting

Reply #7 – March 16, 2011, 11:46:56 PM

When you put the ignition in run without starting does the fuel pump run for a couple of seconds (prime) then shut off ?
If it runs continuously it means the software in the EEC is not running, This is LOS (Limited Output Strategy) or limp home mode.

Car Dies In Neutral When Coasting

Reply #8 – March 17, 2011, 08:39:20 AM

My cougar did the same thing exactly, but in drive... after the car warmed up it acted just like yours... come to find out that the bearings were worn, and oil pressure went from 50 lbs to almost 0 after about 15 min of running....It was just worn out, and to tired to run anymore..