I've been chasing this Idle issue for weeks now. Running a 7747 for the past 21 years in the vehicle and suddenly my idle starts surging, staying high, and just being plain unstable. I replaced the IAC, no difference. replaced and adjusted (0.54v) the TPS, no difference. Today I recieved my EBL flash kit and took my ECM out to work on it. Since I had to drive to the gym tonight, I tossed in a spare 7747 I had on the shelf. Low and behold, the idle is back to normal. The normal high idle in open loop and then as it warmed up it went down to the normal 650 RPM (ish). Shut it off, let it sit a bit and started 1 hr later...still idling smooth as silk.

Is it possible my original ECM is faulty? Now Im wondering if I should be soldering in the new EBL board since I potentially have a problem here. Is there some sort of non-volatile memory in the ECM that is stored and perhaps got effectively "reset" by swapping out to the other ECM? Is it possible the bin on the chip got corrupted at 21 years?

 

It is possible that the original ECM has a problem. Pop the cover off and check the two 16-pin DIP chips by the harness connector. Those are the drivers for the various solenoids & relays.

Any signs of damage will confirm that it is bad. Most of the time a new driver can be installed to fix it.

There is NV RAM in the ECM. It holds some status flags and the BLM cells.

Can always try putting the original ECM back in and see how it is. Otherwise I'd be installing the EBL in the ECM that is in the truck now.

RBob.

 

x2

 

...I wish I could....but.... I already proceeded to de-solder the board from the old one. When I get home from work I"ll do the visual inspection which RBOB suggested and see what I find.

My only aprehension about using the "good" ECM is that its a reman!