High Idle Switch

[Da67goatman]

It's not too often I have to come to you guys for help...so when I do you know its going to be interesting.   I've got a 1992 fullsize Blazer with same the TBI 350 from our body style and just converted the AC to On-Board-Air and would like to come up with some kind of high idle switch.  Any suggestions?  I was thinking of probing the Cruise control and trying to rig up an override that would signal the cruise cable to hold throttle open a little but i'm no electronics guru so it may be a bit over my head to tackle by myself.  Other thoughts or suggestions would be much appreciated.

[bd]

Factory TBI has an active idle system that should maintain a stable idle speed regardless of minor fluctuations in engine load.  It accomplishes nearly seamless load compensation through dynamic ignition timing and IAC adjustments. 

What symptom are you attempting to correct?

[roundhouse]

I assume he wants to bump up the idle when using the onboard air


I have just the opposite problem
I want to reduce the idle speed and get the rpm to drop quickly when I shift gears

Ours has a hanging rpm.  When i take my foot off the gas and push in the clutch it takes too long for the rpm to drop

There should be some way to fool the TBI To raise idle speed

I installed EFI from a 90 mustang on my 74 bronco and had the same hanging rpm problem and just unplugged the idle air bypass and am trying to rig up a way to switch the fast idle on and off
There has got to be a way to do it

Binder planet.com has the best TBI gurus
First question they will ask you is for a data log of the computer

There is some software you can get that will record everything your TBI is doing and the gurus can use that to figure out a mod

Raising the idle should be pretty easy
You could use a fast idle selenoid from a carb setup or I know the early 90s dodge pickups used a TBI with a fast idle selenoid that simply bumped against the throttle plate
Where the cable from the gas pedal attaches to raise the idle a little

THere also should be some way to use a variable resistor to fool the computer into thinking the IAC isn't open as far as it really is

[c0olburn3r]

seems to me that if it takes too long to drop the idle when you push the clutch in, you are running rich either on the choke or you might have a vacuum leak my brother, check it out first
Good luck

As for the first post if your TBI is not responding to the idle when the ac is kicking in, check the the idle sensor it might be going bad, do not attempt to raise the idle on the throttle body, when you put it in gear the computer takes over and all you will have is a high idle when in park.
Good luck

[bd]

Factory TBI has an "idle RPM adder - A/C on" as an ECM constant.  Any tuner with the appropriate software can bump the idle when the A/C is on.  However, I recommend that you make sure there are no existing problems before making changes - otherwise it's like painting over dry rot.