High idle when warmed up
 

When first started, car will idle around 900 rpm. After driving 5-10 mins and coolant temp gauge goes to ~12:30 mark, when I'm idling, will idle anywhere between 1400-1800 rpm. This is a 1.6 with a TEC3 standalone. I'm not using the IAC (since I'm not using the OEM ECU, and the TEC3 doesn't support the stepper type). A couple other things I did: removed the air control valve on top of the intake manifold (has small coolant lines going in and out). Also, I read the coolant lines going to the throttle body really only matter if you're running in cold temps (prevent frosting up of the TB), which I don't, so I removed them as well.

Any ideas why it will idle higher when it's warm? I would think it should be the other way around...:confused:

All things equal a warm engine is "easier to run" You've eliminated the iac which is the only thing to control idle besides the thermal pellet in the air control valve, which you've also eliminated. That valve adds more air when cold to assist the iac. I thought the Miata iac was a solinoid. The tec3 can control those. Sounds like your idle is "set" at +/-1600rpm and it has no means to raise it for a cold engine.

http://www.directignition.com/pdf_files/tec3.pdf

See page 33 and 37 and 107

They also say T3 supports stepper type.

See page 7 for support features

the 12:30 mark for the water temp is what bothers me.


I don't believe he eliminated the IAC valve, just the coolant lines that pass below the TB, and the vavle on the manifold that controls the flow.

My '94 has a thermal pelet in the valve but it's mounted on the bottom of the throttle body. It opens an additional air passage when it's cold to assist the iac. When I bypassed the cooling lines to it I had all sorts of high idle issues when hot almost like he mentioned. hmm. He is correct in the purpose of the cooling lines at the TB for defrosting but it serves idle as well. I missed the 12:30 temp but a high idle could keep the engine a bit warmer. Fans working? if so maybe time for a thermostat.

btw mcsinc. I'm running a standalone too. EMS

Scott is it? Do you have that valve handy on the 1.6 plenum? See if there's some sort of idle air passage in it (and a thermal pellet).

I looped the two coolant lines off my air valve. Put a cap on the two bungs on the TB, and one on the block, and one on the thermostat housing. I don't have any issues.

https://www.miataturbo.net/braineack...e_passages.jpg

the air travels in from the intake and out beyond the butterfly valve.

The IAC valve is still there, but it doesn't have an electrical connection to anything.

My car has always run at 12:30 (or maybe closer to 12:00 if you're splitting hairs -- I can just see the middle white line on the left of the needle)

But is the idle air valve still there? If it is block it off. It might be closed when the engine is at opperating tempature but if the intake manifold heatsoaks to the opening temp then idle can drift. It also looks like there may be a bi-metalic spring in the throttle body as well?

Braineack I have a 1.8L and my thermally controlled iac is in the throttle body. I plugged that and my idle problems went away. I have the coolant lines bypassed but it still would wander open now and then when the engine was very hot. When the cooling lines were attached my idle was fine.

are your fans constantly running when it's at that mark?

The "air valve" (from Braineack's diagram) is not there. I have blocked it off with a plate that is sealed using Permatex Copper Gasket sealer. I'm wondering if this seal is leaking when the temp of the intake manifold warms up?

Not that I have noticed...the temp needle is and always has been just to the right of the vertical line on the "thermometer pic". Even before the turbo install and coolant reroute. I use a 50/50 coolant/water mix and redline waterwetter.

I don't remember the settings I used offhand, but I programmed my TEC3 to run the second fan to turn on and off within the temp range of the first fan. According to the CLT on the TEC3, the fans turn on and off and keep the coolant temps within the normal operating range. Maybe it's just how the needle is calibrated??

Looking at the air flow of Braineack's diagram, why is there two airflow passages from the ISC? I can understand the one on the right...The ISC is open with a cold engine, lets extra air flow through the small passage in the ITM. It is most liekly a bypass when the ISC is closed, but without it, wouldn't there just be "dead air" in the air pipe?

Is the ISC the same as the IAC? (different name, same purpose, kind of like AFM and MAF?)

one is used to open the coolant passage valve, the other goes straight into the manifold.


blobking the plate wont do anything. I plan on doing the same, right now my coolant lines are just looped off the air valve.



if anythign I'd blame the fact that you're not controlling the idle valve.

wouldn't the ISC do the opposite though? (opens when engine cold, adds air through the small channel in the intake manifold)

does the TEC have any air density settings? is it possible that once warm it does something odd? or maybe a bad cold-start setting or warmup enrichment or something?

IIRC, the cold-start setting just works for either the first or 20 secs.

With warm-up enrichment, it adds pulse width dependant on coolant temp. I don't think I did much with this setting, but I wouldn't think it would make enough difference to make the idle go to 1600.