2G Put in new ECU, idle drops very low while in neutral while driving

[Junzu]

97 Mitsubishi Eclipse GST, manual. Stock 97 GST ECU for Stock car. Posted this as a thread but was moved for some reason, need help.


Idle drops so low that car almost wants to die while driving and in neutral... all other gears are good, normal RPMS. At a stop in neutral it's not as bad, 750 is base idle and it idles now at 500ish. All after I put in new ECU... is this normal? The stock ecu with my stock car does not require tuning. Is it just adjusting? Or something else?

 

[1990TSIAWDTALON]

Can you adjust the idle stop so that the throttle plate doesn't close as far, bringing the idle up a little bit?

 

[Junzu]

Can you adjust the idle stop so that the throttle plate doesn't close as far, bringing the idle up a little bit?

Sure I'll try that, but will that be a bandaid to a larger issue? Or could this be just normal adjusting? Have not had to replace my ECU before, did it because I need to pass smog and old computer was junk

 

[Vegas Smith]

It's possible that the install of the new ecu has reset the isc and the car is having to "relearn" the idle control through learned idle adjust feature. I still wouldn't expect this to happen but I can't think of anything better.

 

[Junzu]

It's possible that the install of the new ecu has reset the isc and the car is having to "relearn" the idle control through learned idle adjust feature. I still wouldn't expect this to happen but I can't think of anything better.

Should I just keep running it for a little and it will adjust automatically? If not I'll have to throw old one back in and see if that fixes issue

 

[Vegas Smith]

Should I just keep running it for a little and it will adjust automatically? If not I'll have to throw old one back in and see if that fixes issue

Well, if the idle was set correctly originally then I don't see why it wouldn't eventually adjust now. I wouldn't expect it to take longer than 15 minutes or so. Your new ecu might be damaged in the isc drivers and that could cause weird behavior in idle control. I'd take the new ecu out and see if there is any burning or bulging at the isc driver. That's all I can think of.

 

[Junzu]

Well, if the idle was set correctly originally then I don't see why it wouldn't eventually adjust now. I wouldn't expect it to take longer than 15 minutes or so. Your new ecu might be damaged in the isc drivers and that could cause weird behavior in idle control. I'd take the new ecu out and see if there is any burning or bulging at the isc driver. That's all I can think of.

Thanks. New ecu is pretty good looking, no stains or any sign of trouble, my old ecu was stained to shit

 

[Sirius1995]

clean throttle body and mark tps angle, adjust if needed after cleaning the throttle body, also replace the gasket for TB, ecu might need to relearn but you can just do hard reset for the ECU, disconnect the battery and hook up positive and negative terminals together for 15minutes, that will do a hard reset and might fix your problem, also make sure that all the connectors are good and attached, and did you unplug the battery when you changed the ECU?

 

[Junzu]

clean throttle body and mark tps angle, adjust if needed after cleaning the throttle body, also replace the gasket for TB, ecu might need to relearn but you can just do hard reset for the ECU, disconnect the battery and hook up positive and negative terminals together for 15minutes, that will do a hard reset and might fix your problem, also make sure that all the connectors are good and attached, and did you unplug the battery when you changed the ECU?

Good advice, no I did not disconnect the battery

 

[pauleyman]

Did you go through base idle adjustments? Ecu merely takes inputs and works with that. Just like any computer. At this point we are assuming everything is in good working order. If so you may have to adjust idle via biss screw. It's well documented. Please see the resources on this site.

Such as

https://www.dsmtuners.com/threads/top-10-most-popular-dsm-q-as.55410/

Other resources

https://www.dsmtuners.com/pages/resources/

 

[Junzu]

Did you go through base idle adjustments? Ecu merely takes inputs and works with that. Just like any computer. At this point we are assuming everything is in good working order. If so you may have to adjust idle via biss screw. It's well documented. Please see the resources on this site.

Such as

https://www.dsmtuners.com/threads/top-10-most-popular-dsm-q-as.55410/

Other resources

https://www.dsmtuners.com/pages/resources/

I did not adjust idle after putting it in, thanks!

 

[Junzu]

Update guess I just needed to run it for a little longer oh, everything's fine. Really only tested it for less than 10 minutes yesterday... too hasty

 

[Sirius1995]

Good advice, no I did not disconnect the battery

well there you go

 

[pauleyman]

I would recommend going through the resources page and just browsing. You will catch up on decades worth of trial and error and diagnosis so you have a good understanding of the car before you starting modding or need to make other repairs.