Seems like engine cuts out at idle, no CEL though, HELP!!!

phils89sc

Registered User
My 89 SC has been doing something very weird for the past few days. It starts and idles fine. After it warms up, say I am at a stop light with the car in gear and the a/c on, maybe also when it is off, the idle will drop a little too low, and then, it seems like the engine will cut out or there will be an instant loss in idle speed to make it appear that the engine is going to stall, then it catches and goes back to normal idle. This can happen two or three times per minute. I have no problems off idle and no issues with driveability or power.

Another weird thing it does, when you start it cold, like in the morning, it does not do the normal high idle and slow drop down to normal idle. What it does do is start up, idle goes to just over a grand, then suddenly drops down to normal idle speed. If you start it after warming up, I will then get the normal momentary high idle, but then as it is dropping down to normal, it will do till about 1100-1200 rpm, then 'fall', like it is cutting out to a normal idle. All the other SC's I have had, when you start the engine cold, it goes high idle, then slowly drops back to normal idle.

Could this be a problem with the IAC?
 
I think I had similar problems from a BAP (barometric pressure sensor). You can test it with a multimeter that reads frequency.
 
BAP...Where is it?

I think I had similar problems from a BAP (barometric pressure sensor). You can test it with a multimeter that reads frequency.

Is that the same thing as the MAP sensor? Located on the cowling on the passenger side? Would it throw a code?
 
It's similar to the MAP. The main difference is that the supercharged cars' sensor is not connected to the manifold. It is supposed to sense atmospheric pressure only, so it is just vented to atmosphere. The non-supercharged cars have a vacuum line between the manifold and the sensor. The actual sensor itself is the same, though!

I don't think it threw a code for me. I could be wrong. I was getting some rough idle and stalling problems at stoplights. I tested the BAP and got some readings pretty far out of range. I replaced it, and the problem went away.

Now, I know it's not always that easy. But it might be a good place to start. Here are proper test values:

http://www.fordfuelinjection.com/index.php?p=27

(I really like that website!!!)

If you need instructions on how to test it with the multimeter, just let me know.
 
if battery was unhooked recently that is normal for 2 or 3 days till it learns to idle again . or blown memory fuse under the hood .. other than that im thinking fuel pump fuel filter or fuel pressure regulator . also 1 time on left turns my positive batt terminal was touching the hood shutting the car off

thanks
ralph
 
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if battery was unhooked recently that is normal for 2 or 3 days till it learns to idle again . or blown memory fuse under the hood .. other than that im thinking fuel pump fuel filter or fuel pressure regulator . also 1 time on left turns my positive batt terminal was touching the hood shutting the car off

thanks
ralph

If you are having to rely on adaptive to correct your idle after a reset, then you either have a mechanical problem that needs sorting or you have done mods that haven't been tuned for.

I'd say IAC issues and it needs to be replaced.

Fraser
 
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