IIRC, Paul has done this, don't know for sure of any others. How do you maintain an idle without the valve?

I'm having a high idle issue, and I can't seem to cure it. I tried to adjust the screw on my idle valve, and it won't budge. So if I can just get rid of it, all the better.

 

I don't use an IAC valve, but I have no a/c or ps and use a Link ECU.

No start up issues or idle drop/stall.

 

No AC, PS, or stock ECU here either.

Mainly what I want to know, other than if it can be done on my 1.6, is how to control the idle speed once the valve's gone.

 

You have an idle screw on the top of the throttle body that will adjust idle speed if its not clogged with carbon.

Since you tried doing this, you might want to take it off (difficult but not impossible) and clean it and the passage.

The other way is to mess with the set screw that controls how much the throttle plates close. However, if you mess with this you have to reset the TPS adjustment.

 

That's pretty much it. You'll be able to influence idle speed a bit with fuel and timing, but once the IAC valve is gone, there's no such thing as "control" per se. You turn the screws to get it to where it does not stall when cold, and live with whatever RPM that winds up producing when warm.

Actually, that's not entirely true. If you want, you can still install a "fast idle valve" of sorts. This is a simple on/off vacuum leak that you open when the engine is cold to let a bit more air in. You can use the stock charcoal canister purge valve to do this by removing the hose that goes from it to the canister, and the controlling the valve either manually or with the ECU.

 

Great, thank you both.

These screws on the throttle body, where are they?

I suppose my idle valve must be clogged then. I'll give that a shot.

 

Joe pretty much nailed it. My idle is 900rpm when cold and about 1100rpm when warm. I have no IAC

 

A blockoff plate is needed to cover the hole where the IAC was, right?

 

Screw, I should have said. The only one I am aware of is on top of the throttle body, under a rubber cap:



There is no official adjustment procedure for this screw that I am aware of. It's set at the factory, and you're not supposed to touch it after that. For all I know, they may have used purple loctite on it.


And yes, if you have removed the IAC assembly then you will need to block off the gaping hole on the underside of the throttle body, or else your engine will idle at the rev limiter.

 

Oh, that's the screw I was talking about before.

 

No adjustable manual throttle stop on the miata throttle bodies? I know my nissan one has it and so did my old honda ones. Allows you to physically control where the throttle body closes, instead of one of those bypass screw style ones.

I also run no IACV and no issues that bother me.

 

Well, yeah. There's that. I'd guess it's a pretty coarse adjustment though.

 

?

 

 

I've found I could use mine to dial it in pretty well. Just have to be gentle and ensure you hold stuff tight while tightening it.

 

 

Yes, the stop is there but it is not the one circled in Joe's photo. BTW, the circled item is supposed to be the place to adjust idle speed. It is meant to be manually adjusted. This is not like some of the later vehicles that are not meant to be adjusted.

The throttle stop has an 8mm hex nut with a small slot on the stud for adjustment.

 

Thanks for all your help dudes, the deed is done!






I still can't get the idle screw to budge, but I managed to get the idle down to 1000 RPM by backing off the throttle stop, which was an 8mm nut and an allen-headed stud on my 1.6.

 

You can set your ECU for 0 advance at idle, then adjust your idle to around 1100 with the idle screw or throttle stop. Then leave the timing at 0 for 1100RPM, and ramp it up to about 15deg at 700RPM. Worked on the Miata with A/C and Power steering. Without A/C you could probably get a good 900RPM idle that way but cold starts might be a little annoying.
You will have to richen up the idle mixture to get a steady idle at 0deg advance.

 

Dear, I have just read your post, if you are still active member please can you give me more instructions. Mine is Cougar 2.0 1999 but with replaced Zetec engine 1.8. I spent hundreds of dollars (here in Macedonia - Denars) to replace some sensors, some this some that, and it is still a wasting of time and money. So, few days ago, when I unolugged the harness connector from purge valve, realised that idle is far better than before. Also when unolug the IAC on hot car, everything was almost perfect. But on cold car, it dies immediately after start if I not press the gas pedal. The trottle body does not have stock screw to adjust base idle. I thaught to make some modification if it is possible, with some thermal switsh, sticked on the engine,that IAC positive will run through and to be closed on cold , and when engine get working temperature, to be disabled the electricity to iac (like unplugged). Also I can use purge valve as you wrote, but how can tonthat to control automatically, just to warm the engine and left close? Thanks in advance