Idle problem.Thought fuel, but it was bad ECU

A little back-story on the Dart.
This car is a driver. So when I built it, I went for reliability and street ability. . Some time around 2000 I got a Diplomat cop car with 39K on it.
I pulled the 318/360 engine, lock up transmission and 8-¼ rear from the cop car an put them in the Dart.
I like spread bore Q-Jets, so I took off the electric one that came on the cop engine and put a junkyard GM one on it instead.
(I run junkyard Q-jets with modified Mopar style throttle levers on the base,)
This car has been driven coast to coast and back. And for the last six years I’ve been putting 80 mile a day, five days a week, on it as a commuter.
Some day I’ll get my oil change records and figure the miles.

So for a while now, the Dart’s had a issue with the idle.
Not a problem for driving since, I’m on the interstate most of the time and just keep my foot in it when it has acted up at the traffic lights.
I figured it was something in the carb idle circuit.
Funny thing.
It would be OK sometimes and sometimes it would sort of have trouble idling and then pick back up.
Or idle up and drop down.
Like something was clogging the idle bleeds or something.
I’ve taken the carb apart clean it and checked everything more than once.
Well, last week the car died on me just before I got on the interstate and then it died while actually on the interested. It restated both times.
But that did it.
Yesterday I went through the whole fuel systems.
New fuel pump. (Stock of course).
Even dropped the tank for a peak and it looked pretty good for the age.
The new fuel-sending unit I put in there in 2003 was OK.
No clogs, trash or gunk.
Not finding anything in the fuel system, I started checking the electrics.
I started swapping the ECU and that did it.
When I built the car long ago, I got a junkyard Orange box.
That must have been almost 15 years ago. It was fine then.
The thing must have deteriorated over the last few years.
When I put other ECUs on the car yesterday for testing, not only did it idle like new.
But the Idle speed picked up and I had to tweak the screws back down. And it is smooth now. It was sort of lumpy before.

Lesson of the story is to check your ECU if you have an idle problem
Weak spark at idle (sometimes) I guess. It was trying to warn me.

I tried both 5 and 4 pin types for testing.
You know, they say a five pin won't work on a single ballast set up. But swapping them around for testing, I didn't have any problem. Both worked.

Oh, and I've got to check my mileage.
The fuel gage didn't hardly move driving today.
I know it's better.
Maybe I'm going to get 50MPG now.:cheers: (ha)