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· Speed limits = Guidelines
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2,352 Posts
Discussion Starter · #1 ·
I have a custom intake mani that that deletes the IAC valve...the car starts and will keep itself running until warm, but it does it poorly

Seeing as how the Idle% vs Target table has no purpose now, i was going to flat line it at 0 and uncheck the stepper motor option

As for my question...what parameter should I be focusing my attention on to impact the idle now that the IAC no longer can do that. Looking at it, I figured the Fuel Offset vs RPM would have the biggest effect on the idle...seeing as how the air is no longer modulated, I will just modulate fuel to compensate. The startup cal made no use of this table...Am I correct in my thoughts on this?
 

· LEADED FUEL ONLY
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I never understood why people disable what makes a motor idle and wonder what they can do to make it idle. It's like taking the TPS off the car. The IAC (ISC) is a major system in helping the engine do what it was intended to do; run.
 

· Speed limits = Guidelines
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Discussion Starter · #3 ·
I never understood why people disable what makes a motor idle and wonder what they can do to make it idle. It's like taking the TPS off the car. The IAC (ISC) is a major system in helping the engine do what it was intended to do; run.
on carbureted engines, its known as the choke, which is only needed during warming up...same goes for the idle control motor, it is not needed on a warm engine...and for a cold engine, it only makes it warm up a bit better...

when i start my car up (without the iac) it idles like 500-600 rpm, and gradually builds itself up to its normal idle at like 900 as it warms up....if i blip the pedal while its cold it sometimes hesitates a bit, may even stall sometimes...but when its warm you wouldnt be able to tell the difference between having it and not having it

for me at least, anything thats not necessarily needed like that, i dont want on my car
 

· LEADED FUEL ONLY
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I dunno.

I know I can tell my AEM to idle at 600 and it'll do it or tell it to idle at 2k, and it'll do it. It would seem to me that one would need this valve to adjust idle. Only other way to adjust idle would be the idle screw. There are no other means of adjusting idle speed other than those two methods. I guess one can do it with timing, but that's another conversation that I know little about. :)
 

· Speed limits = Guidelines
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Discussion Starter · #5 ·
It is a bit more difficult to tune idle without the IAC, but it is possible...Theres pretty much 3 major things that could be adjusted to effect how the car idles...air, fuel and ignition...I no longer have the ability to adjust air, so that just leaves me with fuel and ignition...i just gotta work with that
 

· LEADED FUEL ONLY
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If that's what you believe, then one could adjust the cells that deal with idle and it'd be very simple. There is an idle plateau that the car should sit on. Timing will influence idle *quality*, but it will not dictate idle *speed*. Same with a/f ratio.

The only way to increase RPM, is to give the engine air. That's the ONLY way.

You're going to have to open up the idle screw. That's the only way you have to adjust your idle. Who knows what that'll do to cold start situations.

Seriously, throw an IAC back on it, and worry about drivability and WOT. Not idle.
 

· Speed limits = Guidelines
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Discussion Starter · #7 ·
If that's what you believe, then one could adjust the cells that deal with idle and it'd be very simple. There is an idle plateau that the car should sit on. Timing will influence idle *quality*, but it will not dictate idle *speed*. Same with a/f ratio.

The only way to increase RPM, is to give the engine air. That's the ONLY way.

You're going to have to open up the idle screw. That's the only way you have to adjust your idle. Who knows what that'll do to cold start situations.

Seriously, throw an IAC back on it, and worry about drivability and WOT. Not idle.
not quite that simple to just put it on...i no longer have the stock mani, which no longer gives me the ability to just bolt it back on...id have to take the mani off and fabricate something to make it work...not worth it

ive been messing with the idle adjustments lately, the fuel and timing ones...and the idle is pretty stable...its at a steady 800-900 rpm most of the time at about a 15:1 mixture...you wouldnt even be able to tell i was running without it without physically looking for the valve
 

· Moo
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428 Posts
Just wait until those cold spring and fall days. :) Steady idle at operating temp on a 70F day is easy. Think about cold start, warmup, varying loads, varying ambient conditions, etc.

You could plumb in a different IAC valve, one that uses hose fittings or something that would mean simply tapping a fitting in to the manifold.

I personally think it would be worth removing your plenum to fab in an IAC valve.
 

· Registered
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My intake mani does not have a provision for IAC either. I plumbed a -10AN fitting and remote mounted my IAC on the firewall and connected it with a hose. It works perfect that way. Idle without an IAC is a PITA.

Your best bet is to setup the car so it warm starts/idles the way you like it. Plan to have a slightly higher idle when warm and it should help with cold idle. Odds are you'll have to keep your foot on the throttle for a minute or two regardless.
 

· Speed limits = Guidelines
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Discussion Starter · #10 ·
so far the range ive had a chance to test the car out in is from about 55-80 degrees, in which is seems to start up and idle itself til warm with no help from me needed

it does appear strange to me that the car is not giving me more problems without the IAC. when i was removing it, I was expecting to not be able to keep the thing running with some pedal input
 

· 1100+rwhp member
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I got my car to idle without the iac with my old manifold without a problem. Cold start it would run a little rough for a couple of seconds and that is about it.
 

· 1100+rwhp member
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LMAO!!!! I guess your right Hey we may have a day or two that it gets cold down here you know.
 

· wastegate hose is pulled
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Even my chainsaw has a choke on it! If it idles at 500 rpm on a 55 degree day, imagine what it will do on a -10 degree day when it will need a ton more air to start and the battery is at its weakest. IAC is not something you should toss. Plenty of options for remote mounting if the intake manifold doesn't have a flange on it.

Fuel and timing ramps will speed up and slow down the engine once it is running but, it gets ugly with glowing exhaust manifolds and overheating/skyrocketing oil temps etc. Just wait until your crappy accufab (er whatever) throttlebody doesn't close all the way or one of the accessories loads the engine down more at idle.
 

· Speed limits = Guidelines
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Discussion Starter · #15 ·
Even my chainsaw has a choke on it! If it idles at 500 rpm on a 55 degree day, imagine what it will do on a -10 degree day when it will need a ton more air to start and the battery is at its weakest. IAC is not something you should toss. Plenty of options for remote mounting if the intake manifold doesn't have a flange on it.

Fuel and timing ramps will speed up and slow down the engine once it is running but, it gets ugly with glowing exhaust manifolds and overheating/skyrocketing oil temps etc. Just wait until your crappy accufab (er whatever) throttlebody doesn't close all the way or one of the accessories loads the engine down more at idle.
yes, but the chainsaw does not have the advantage of being EFI, not much tuneability to keep it running

im sure i would have some problems during the winter, but i take insurance off the car and keep it inside for that time of year...the cars never seen a snowflake, or a temperature below 40 degrees for that matter
 

· Moo
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PA should see similar weather to Ohio. That means beautiful 60-80F days in the spring and fall with evenings that can dip in to the 30's pretty quickly. But hey, maybe you only drive your car when it's 70F out. *shrug*

Have you put the new plenum on yet? If not, disconnect the IAC wires while it's running at your desired idle and at full operating temp. This should leave the IAC open where you need it so you can experiment.
 

· wastegate hose is pulled
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yes, but the chainsaw does not have the advantage of being EFI, not much tuneability to keep it running

im sure i would have some problems during the winter, but i take insurance off the car and keep it inside for that time of year...the cars never seen a snowflake, or a temperature below 40 degrees for that matter
Gas engines run very similar, be it EFI or carb. They need airflow adjustment to control engine speed properly. If you want to ditch the IAC, get a Diesel. You can toss the throttle then too.
 

· Speed limits = Guidelines
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2,352 Posts
Discussion Starter · #20 ·
Gas engines run very similar, be it EFI or carb. They need airflow adjustment to control engine speed properly. If you want to ditch the IAC, get a Diesel. You can toss the throttle then too.
they are similar in some ways but a carburetor does not allow much tunability....there arent many adjustments you can make on a carb that wont create accross the board changes...with efi you can focus on idle without effecting anything else...which is one of the main reasons carbs are a thing of the past for the automobile industry
 
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