I was running the stock p28 basemap preloaded on the s300.

Swapped the chipped for stock. No surging idle. Drives smoother as well. STFT and LTFT under %.8.

After throttle, idle hovers, then settles at ~750

 

There ya go. The chipped ECU is clearly the issue. Sounds like some proper tuning of the chipped ECU is in order.

Still no CEL I assume.

 

No cel. I know something is amiss. I don't like how my idle roams before it settles to spec.

 

Post a video of the tach behaviour. But you're clearly moving in the right direction and close to normal now.

 

 

I think that can be fixed by performing the proper idle adjustment for the stock ECU. Do you have the 96 Del Sol service manual?

 

I have 96-98 civic service manual. I can't find a pdf of a USDM del sol specific service manual

 

Do you have an OBD2 code reader that also reports live data such as engine rpms?

If so, follow this procedure:




In step 5, keep turning the idle screw to the lowest idle speed where it will still hold the spec idle speed. Does that make sense?

 

Yes, I can monitor my rpm. Give me 10.

 

Please read the last sentence I wrote in the last post.

Do you have a timing gun?

 

I do not understand the sentence. No timing gun at this moment. I will have one tomorrow at 10 am.

 

There's usually a range of idle screw turn positions that will yield the spec base idle speed of 450 rpm. In step 5, keep turning the screw in the direction that reduces the idle speed just until the engine can still hold at 450 rpm. Make sense now?

 

Understood. I cannot achieve an idle of 450 with the idle screw completely bottomed out.

I took notes during the idle procedure:
Step 5. No load idle speec- 680
Step 8. After ecu reset + 1 minute wait-780
Step 9. Headlights only- 885
Step 10. Heater on HI ac on-810

 

With the IACV unplugged?

 

Yes, the IACV was unplugged.

 

How close to 450 rpm do you get?

 

680 rpm.

 

Is the throttle cable adjusted properly with some slack?

Has anybody ever messed with the throttle stop screw?

With the IACV unplugged, can you lower the 680 rpm base idle speed to 450 rpm by covering the hole leading to the IACV inside the TB?

Is the stock ECU still installed?

 

Throttle cable has appropriate slack.
Throttle stop screw has unbroken yellow marker line. No tampering evident.
Covering the iacv hole results in the engine dying.
Stock ecu (obd2 p28) still installed

 

The unplugged IACV is bypassing too much air to the IM. Have you cleaned the IACV?

Good. Leave it installed until the problem is pinpointed.

 

It's actually an aftermarket iacv. I replaced it awhile ago being naive. Have not cleaned it.

 

Try thoroughly cleaning the aftermarket IACV with brake cleaner. If the high base idle problem persists, scout junkyards for 96-98 Civic 2-wire IACVs. I assume they'll be the same as your original stock one for the 96 Del Sol.

 

I'll have to post results tomorrow, I do not have any brake cleaner on hand. I was planning on heading to the junkyard for an oil pan and valve cover anyway, I'll keep an eye out.