A big F U to my Cougar's occasionally cranky idle.
Reply #3 –
How has it been since then? From that post, you had a bad idle when you went to work, and then two restarts that were okay. I'd definitely give the ECM a week or so of *varied* driving conditions and styles to accumulate the collection of false readings to ignore, as well as any other data storage it does.
I've owned 5 EFI 5.0's at this point, and they all have tended toward a higher idle when unloaded once they're warmed up. It seems to take anywhere from 1 to 5 minutes of just sitting there idling for it to come back down from 1000-1100 to 800 or so where it belongs. I chalk THAT one up to whatever routine is built into the software.
I don't know how these systems compare to modern EFI...all I do know is that my Crown Vic pretty much idled and ran like a new car, my '87 Grand Marquis I now have does the same. How refreshing. Why? Because it hasn't been modified yet. :) That's gotta be where you run into trouble. Someone that actually tunes a PROM for your ECM, and who knows the software well, can probably modify some parameters to make up for modifications done to the engine. We all know how terrible the throttle response is on an S.O. engine compared to, say, a Trick Flow top end setup with a 70mm throttle body. Very snappy. And so you basically turned up the gain on a (relatively speaking) overdamped control system. The engine responds slowly and surely to the inputs of open/closed IAC. Now, with high-flow everything, it makes a the same opening and the RPM jumps beyond anything it expected. It will learn to make more gentle, smaller adjustments because of the quick response, but until then it'll fall into a seemingly never-ending oscillating loop.
This is where you need someone who really knows the EEC-IV well, and I guarantee (well almost guarantee) that there will be parameters for seemingly trivial settings like "how quickly to ramp up the rate at which the IAC opens/closes". What Tom described is technically this, just a physical mod, not a computer parameter. Your mileage WILL vary, as they say.
My red cougar has the IAC unplugged. I do this because of the high idle, and because I don't really love the fact that on a cold startup, the engine zooms to 2 grand and sits there. I'd like it more gentle. Below 50 degrees, I have to sit there and help it idle for a couple minutes like it's freakin' carbureted. In the summer? Not a problem. Just starts and idles like a.....warmed up carbed car :hick:
At SOME POINT (lmao) I'll get that and the black car professionally tuned. I guess Mustang Magic on LI is supposed to do OBD-I Ford and do it well...?
Topic: A big F U to my Cougar's occasionally cranky idle. (Read 2010 times)
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