I'll try to make this quick..

From what I read once, our ECU gets a reading from somewhere (coolant sensor on bottom of rad?) that tells it the TB is going to be at cold start partial open position.

Anyhow, from what I imagine, this is why cold start removed TB's will have bad idles until warm. I guess you gotta use the foot to hold the throttle open as the cold start TB actuator would or you get bogging due to a highly rich mixture.

Is this true? Is their programming in the ECU which runs a rich mixture expecting the TB to be propped open to about 1500 rpm's?

If this is true, can it be diabled via a sensor?

Also, is it possible.. dont flame me.. That this may be a possible flooding issue? i.e. stuck in cold start enrichment fuel curve??

Anyhow, any thoughts would be appreciated.

oh yeah... I know, get a Haltech.. lol

 

No. The car would realize its not revving to 2-3k and adjust fuel curve.

I think they just idle like crap because they are cold.

 

So basically, it just reads off the AFM signal and TPS for cold start fuel? That, in conjunction with the TB plates being held open for the higher idle.

I just hear eveyone who removes the secondaries and cold start apperatus have issues with cold start idle .. I just wondered if there was a factor I was overlooking and had heard about a fuel enrichement by the ecu.

In a nutshell, I guess I'm looking for a very detailed explanation if anyone is willing to offer it.

 

There are a few things that attribute to the cold start.

 

No, enrichment during warm-up has nothing to do with the AFM or TPS, that's the job of the coolant thermosensor. When the thermosensor tells the ECU the engine is cold, correction factors are added to the calculated fuel requirements to ensure the engine runs smoothly. There's no need to remove the cold start idle part of the TB when removing the #2 secondary throttles. The two systems are completely seperate and have no effect on each other. I like my car to idle normally when cold, so I left it all in. The #2 secondaries are history though.

 

Mine idles just fine all the time when cold and I have none of that stuff on it. This is true for ambient temps ranging from -20 to 90+ F.

The radiator temp sensor is what controls the high idle cold start function of the ecu. If you cant get a solid idle with that sensor unplugged you have other issues such as vac leaks or a bad ACV/BAC. (I also have neither of these)

 

Thanks guys. Just one of those things thats been eating at me for a while.

Its difficult sometimes for me to see how everything comes together and works. I wish our emmissions system wasnt so damn complicated. I want to rip it all out so bad!

I appreciate the input

 

It can be a little tricky to get a good idle with a gutted throttlebody, but it IS possible. My TII starts bone cold, idles at around 900 RPM, and idles at 750 when warm. Doesn't die or stall at all.

One trick to get it like this is to, with the car warmed up, adjust the BAC until you have about a 600 RPM idle. Then, adjust the primary throttle stop to bring it up to 750. That makes a *world* of difference.

One of the key reasons to gut the throttle body is ease of maintenance and simplicity. That 90 degree coolant hose going from the block to the throttle body is asinine - they did redesign it on the '89-91 cars, but it's still a pain in the butt. But, if you can have a good idle all the time, there's no good reason to keep the thermowax setup on the throttle body.

Dale

 

You might want to rethink this statement:
*the radiator temp sensor is what controls the high idle cold start function
of the ecu.****

And the reason I say that is: The water temp sw at the bottom of the radiator does not have a completed circuit when the water is cold. So the question to ask, is: How would pulling the wires off a incomplete circuit effect anything? Answer: It can't. One of those zero from zero equals zero things. Just trivia. Not knocking anyone. Its just that I've seen that written before...and it ain't quite right.

 

there's two wires which go to that sensor, I assume that when the sensor is cold it closes that circuit.

I know from imperical knowledge that removing that sensor eliminated the high idle cold start function on my S4.

 

When the sensor is cold....the circuit is open. When its hot...its closed. Just a brain teaser.

 

Guys,

Thanks. I really didnt expect to get so much info on this subject.

The reason I asked is that i live in Salt Lake and don't really want to have to fight to keep a good idle in winter if I remove all the TB cold start stuff. I do, however, like how clean it looks with all that crap removed.

I was thinking of just removing the plates, but leaving the cold start. Then, so many people told me how much of a pain that hose is and to remove it cuts upper intake removal time in half.

Anyhow.. thanks again and feel free to add any info

 

With removing the cold start stuff on the TB you should still get a higher rpm start up. You still have the ASV and the other thing.

 

Well, Mine is just two wires hanging in mid air and no sensor in my car anymore and I don't have the high idle start.... Open circuit would be high idle by your rational Hailers, mine has no such thing....

I wonder if i kept that pile of crap? I can test it with the ohm meter and end this once and for all.

 

The AFM measures the volume of air going into the engine. The computer uses that information to calculate how much fuel to inject for a given A/F ratio. The thermosensors tell the computer how cold the engine is and it uses this information to influence what A/F ratio it shoots for. If the computer doesn't see the engine as being stone cold, it doesn't enrich the mixture for a cold engine.

 

While that is true to an extent, the ecu uses a single thermo switch in the radiator to determine the fast idle cold start function.

 

****.... Open circuit would be high idle by your rational Hailers, mine has no such thing...*************

Uh huh. Yes and no. I have come to the belief that we all agree the water themp switch on the 85-88 radiators DOES play a role in the fast idle start (3000 is a runaway horse not a idle{humor}), it is not the only player, because the water temp switch I assure you has a open circuit when the temp is below 59-62 degrees. One wire goes to the ECU and the other to ground. No circuit below approx 60 degrees.


So I really do agree with you to a point. I think there is another player, like the water thermo sensor.

 

Obviously the ecu is using its other temp sensors to make proper adjustments for varied engine temps. I'm simply stating that when I removed that sensor from the loop I lost my annoying 3K cold start idle.

When you have headers and open pipes 3K is enough to summon the cops every time you start the damn car. This was one of my first mods. I've never missed it.

 

The temp switch in the radiator is there for emissions controls only. As well as affecting the operation of the ACV's relief valve, it operates the Accelerated Warm-up System the causes the 3000rpm idle during cold starts. But that just lasts for a short period (20sec?) to get the cats warmed up quickly and reduce emissions. It has nothing to do with the slightly higher idle speed you get during warm-up after the AWS has shut off. The thermowax does this, opening the primary throttle blade slightly to compensate for the fact that cold engines simply don't idle very well. The ECU supplies the richer mixures that cold engine temps require based on the coolant temp measured by the coolant thermosensor, as I said above.

 

I tested my sensor in the bottom of my radiator not that long ago and I could only make it a closed circuit if I put it in my freezer, (ie -18 ish? degrees C.) then as soon as it started to warm up it would go open again..
not sure if my sensor is completely rooted but that was my observation
I also dont have it hooked up at the moment seeing the lowest temp I will ever get where I live is about 25 deg..