Resetting ECM

[cire]

Hello all,
I have been lurking on here for quite some time. It has been a great site to learn about these older chevy’s. It has definitely helped me out. I have been helping my grandfather with his 1990, C1500, with 5.7. He is the original owner. Truck has 129,000 miles. He has always taken care of it. It is in fantastic condition. He is always being asked if he wants to sell it. Especially when he is getting gas. We have replaced a lot of the original tune up parts. It has been having a rough idle on start up which usually goes away after warming up. We were thinking of resetting the ECM just to make sure everything was cleared out and started over with all the new tune up parts. Is it okay to reset the ECM? Will it do any harm? Do you just disconnect the negative battery cable and turn the light switch on for about 15 minute? What is the proper way to start and drive the vehicle after resetting? And any other advise about resetting and restarting would be greatly appreciated. Many thanks

 

[Erik the Awful]

I don't think "resetting" your ECM is going to fix anything.

Check your O2 sensor swings. If it runs rough on startup but smooths out after warming up, that indicates a rich condition. Also, check to make sure squirrels haven't packed the intake full of nuts and nesting.

 

[618 Syndicate]

There is no "reset" for the ECM, and I have no idea why you would need to turn a light switch on after disconnecting a cable.
Who told you that nonsense?

 

[Spareparts]

Unhooking the battery for a while will reset the LTFT but that is the only thing it will do.

 

[someotherguy]

Unhooking the battery for a while will reset the LTFT but that is the only thing it will do.

and clears codes, and loses the memory for the IAC position, etc. etc.

But it's not gonna "fix" anything, that's for sure.

Richard

 

[Spareparts]

Totally agree

 

[victor II]

I don't think "resetting" your ECM is going to fix anything.

Check your O2 sensor swings. If it runs rough on startup but smooths out after warming up, that indicates a rich condition. Also, check to make sure squirrels haven't packed the intake full of nuts and nesting.

 

[victor II]

Try some Seafoam injector cleaner. Also, what tune up parts did you replace? The dist cap/rotor, air filter, wires and plugs could act this way. So could a loose throttle body.

 

[Nad_Yvalhosert]

There is no "reset" for the ECM, and I have no idea why you would need to turn a light switch on after disconnecting a cable.
Who told you that nonsense?

It depletes any residual charge left in capacitors.

 

[cire]

Well, we did the hard reset. Disconnect the negative battery cable. Turned the light switch on for about 20 minutes. Reconnect the negative cable and started it up. Definitely made a difference in the way it runs. Much smoother. We had previously just disconnected the negative battery waited 10 minutes and reconnected. Didn’t make any difference. Depleting all energy from the capacitors with a hard reset was the way to go.