I have had my 89 Fox 5.0 for about a yr now, its been running for about 8-9months. I haven't been working on it in a while. The idle was surging big time then stalling out. I just figured out that the guy who owned the car before me had plugged the BP sensor to the A/C outlet on the vaccum tree. In 89 Ford had switched to a BP sensor which measures the baro pressure shouldn't be plugged. The car runs like a top now. Everyone has been telling me its the IAC and I tried cleaning and replacing that to no avail, so hopefully this helps someone else that searches for this idle problem for months.

 

sounds like a vacuum leak somewhere.

 

No leak just the fact that the 89 has a baro sensor not a map sensor, it was plugged into the a/c outlet in the tree causing it to freak out. The reading it was getting was from the vaccum system which has an a/c delete, not an enviornmental reading from behind the engine.

 

...interesting

 

x2 on interesting. makes me wanna take a look under the hood to see exactly how it's hooked up. just for the heck of it.

 

I just noticed that vac tree on my '91. I was not familiar with it having only worked on my s197 before.

What id the IAC so that I can keep my terms straight. Is that the Idle Control or something?

 

Yeah Gary, it's the idle air control valve. What happens is that over time oil, dirt, etc. gets gunked up in it, or the problem can rise from carbon fouling. As a result, the car sounds like junk. When I bought my fox, the guy who owned it did a full tune-up, but it still sounded a little off; it wouldn't quite idle correctly. When I got it home, the first thing I did was take off the IAC and clean it completely, let it dry, then put it back on. It made a world of difference for my fox.

 

good read here

http://sbftech.com/index.php/topic,119.0.html

 

nice