Hey Everyone,

I recently got a 1993 Del Sol with the 1.5. The issue I am having is a surging idle when it warms up. I have bypassed the FITV, replaced the IACV, bleed the coolant system, and even bypassed the IACV. It will still get a surging idle of an RPM 1K to around 1700. I tested the TPS and it measured good (0.5 closed, 4.5 WOT). I unplugged the vacuum line to the MAP and the idle seems to calm down, but I read that when you do that, it basically put the car in limp mode. I blocked off the PCV to see if it would make a difference, and it didn't.

My next thought is maybe a headgasket or maybe the ECU. I thought I would ask around before I went those routes.

TIA,
Shad

 

Inside the throttle body, the upper port feeds air to the IACV while the lower port feeds air to the FITV.

Remove the air intake system. With the idle surging, use your finger to cover the upper or lower port. Does covering one of these ports stop the surging and lower the idle speed?

 

I haven't done that, but I did make a plate and blocked off the IACV. Wouldn't that do the same thing? It still had a surging idle after it warmed up...

 

The tests are easy and worthwhile.

The IACV hole is used to bypass air to both the IACV and idle adjust screw.

If covering the TB holes with your finger does not affect the surging, then you have an intake air leak (TB or IM gasket) and/or a vacuum leak (IM hose connections).

 

I do that test and the idle straightened out. Does that mean the IACV is the problem? I just replaced it. And I blocked off the whole IACV with a plate and it still had that issue...

 

Details please.

Covering the IACV hole but not the FITV hole steadied the idle speed?

 

Yes, I only covered the IACV hole; I have the FITV blocked off.

 

Your IACV block may be leaking or the idle screw may be leaking.

The idle screw has an O-ring to seal it from leaks.

 

I replaced the idle screw o ring. I have sprayed about 2 cans of carb cleaner trying to find a vacuum leak; still can’t find one. I unplugged the connector and the idle leveled out, was still high.

the car drives great, just the idle is driving me crazy...

 

Remove the IACV and FITV blocks and reinstall the IACV and FITV.

Is idle speed still high and surging when engine is warmed up?

If so, individually or simultaneously cover the IACV hole and the FITV hole inside the TB. Does the idle speed steady and drop?

 

I removed the block on the IACV. I don’t have the FITV anymore. Same issues...

 

I'm trying to determine whether the blocks leak.

Did you reinstall the IACV and then cover the IACV hole inside the TB?

You will eventually need an FITV to achieve proper cold idle speeds.

 

Yes, the IACV was installed when I covered the hole.