Fuel trim question - 98 Civic

[98civex]

Follow the procedure, but keep turning the idle screw to increase the idle speed to see if it becomes steady. If not, try cleaning the IACV.

If you keep turning the screw to increase the idle speed, the idle speed should not rise above 670 rpm because the ECU will note the rise and decrease the rpm to spec.

Are you saying to turn the screw while the IACV is still plugged in?

Does the ECU decrease the idle by changing ignition timing?

 

[98civex]

How does the ECU adjust idle? Does it close the IACV valve accordingly?


Sent from my iPhone using Tapatalk

 

[98civex]

Cool. Just curious, If the idle isn't steady with the IACV unplugged. What would be causing that? It would mean the IACV couldn't be the issue no?


Sent from my iPhone using Tapatalk

 

[98civex]

Correct. However, in your case, the low idle speed (450+/-50 rpm) with the IACV unplugged may itself unsteady the idle speed.

What do you mean exactly?

 

[98civex]

I just tried the idle procedure and with the IACV unplugged the idle fluctuated no matter how much I adjusted the screw.

Even after plugging in the IACV at different screw adjustments the idle would still fluctuate by +/- 10 rpms


Sent from my iPhone using Tapatalk

 

[98civex]

550rpms. Should I go as high as possible? How would adjusting base idle high help with getting a steady idle?


Sent from my iPhone using Tapatalk

 

[98civex]

Yes it was similar to my original idle with the +/-15 rpm of 660-675 never steady or for briefly a second or two


Sent from my iPhone using Tapatalk

 

[98civex]

It may be worth trying 600 or 650 base idle rpm as an experiment. It's up to you.

I'll try it out next time I have some time. What do you think is causing the fluctuations?

Now I'm curious if every car has a steady/constant idle or same slight fluctuations


Sent from my iPhone using Tapatalk

 

[blandsarcasm]

Fluctuating only 10 rpm isn't really much. You said earlier that your tach reads steady but a digital reading shows fluctuation? When my iac had been acting up I was fluctuating maybe 500rpm. I had a very small vac leak not long ago that was making my idle bob just enough to barely make the needle move a hair but you could hear it fluctuating


Sent from my iPhone using Tapatalk

 

[98civex]

Fluctuating only 10 rpm isn't really much. You said earlier that your tach reads steady but a digital reading shows fluctuation? When my iac had been acting up I was fluctuating maybe 500rpm. I had a very small vac leak not long ago that was making my idle bob just enough to barely make the needle move a hair but you could hear it fluctuating


Sent from my iPhone using Tapatalk

Yes tach stays steady. Only reason I questioned my idle was slight vibrations

 

[blandsarcasm]

Yes tach stays steady. Only reason I questioned my idle was slight vibrations

Both of my cars do this and it's more noticeable with solid mounts. My girlfriends coupe is all factory but it still has minimal fluctuations if you really take notice. Watching my idle on hondata the numbers are constantly changing but it stay within a very tight range.


Sent from my iPhone using Tapatalk

 

[98civex]

Both of my cars do this and it's more noticeable with solid mounts. My girlfriends coupe is all factory but it still has minimal fluctuations if you really take notice. Watching my idle on hondata the numbers are constantly changing but it stay within a very tight range.


Sent from my iPhone using Tapatalk

Yeah mine does too. It's +/- 10-15 below or above 670 rpms

Does your gf's all factory coupe shake a little at idle too?

 

[blandsarcasm]

Yeah mine does too. It's +/- 10-15 below or above 670 rpms

Does your gf's all factory coupe shake a little at idle too?

Very very subtlety yeah. I've never been alarmed by it. Like I was saying it's very noticeable in my hatch with hasports. You can hear the vibrations and hear them fluctuate


Sent from my iPhone using Tapatalk