Electronic High Idle Retrofit

SmokingRocks

Buy it, build it, bash it... Repeat
Joined
Oct 6, 2014
Messages
2,901
Location
Colorado
Does anyone know if it is possible to temporarily input a modified signal to the IAC valve to initiate high idle?

I'm thinking this might be pretty easy on my OBD1 1fz-fe.
 
Joined
Mar 21, 2010
Messages
2,910
Location
SK, Canada
It's been done using the cruise control system and a potentiometer, but the details in the thread were fuzzy.
 

SmokingRocks

Buy it, build it, bash it... Repeat
Joined
Oct 6, 2014
Messages
2,901
Location
Colorado
@landtank I'm thinking just 1000-1200, just enough to get the alternater off idle.

Looking at the fsm for the IAC it looks like it's as simple as adding some current, protective diodes and picking the idle (S1, S2, S3, or S4).
 

SmokingRocks

Buy it, build it, bash it... Repeat
Joined
Oct 6, 2014
Messages
2,901
Location
Colorado
Yea that sounds like a simple bypass to just trigger the cruise module to crack open the throttle plate. I guess that's a fairly easy solution too.

I'm thinking of tapping into the idle air control valve.
 

ajax1

 
Joined
Feb 7, 2009
Messages
2,177
Or add the hand throttle you might have the pedal already in place some do some don't then just buy the oem hand throttle
 
Joined
Apr 19, 2015
Messages
1,174
Location
Ramona, CA


The IAC valve is a stepper motor with four coils that need to be driven by a stepper motor driver. Each terminal isn't a 'position' that can be just driven to. The ECU drives the stepper motor around for the desired idle level. If you put something in the middle to control the valve yourself you would be fighting the ECU trying to drive the IAC valve to put the idle back. It's really not feasible to do that.



If you want to try to do the A/C idle up you'd have to tap into the ECU's A/C input. This line is driven by a relay called 'Engine Coolant Temp Cut Relay'. You'd have to use some creative diode or relay circuit to cause the A/C clutch to come on when the AC system commands it and also allow the ECU to think the AC is running any time you wanted it to with your 'idle up switch' that you'd install. If you just put voltage on the line A/C input, the A/C compressor will engage as well. You would still only get the small increase that the A/C normally does and couldn't increase it beyond that.
 

SmokingRocks

Buy it, build it, bash it... Repeat
Joined
Oct 6, 2014
Messages
2,901
Location
Colorado
Thanks @sbman I don't have AC anymore so that may be a much easier route, but not sure its enough of a increase in RPM? I don't have experience with it.

May be easier to tap into the cruise control
 

SmokingRocks

Buy it, build it, bash it... Repeat
Joined
Oct 6, 2014
Messages
2,901
Location
Colorado
I'll try the AC idle up tonight and see what RPM's I get out of it. Should be really easy since the system has been removed.

Do you know off the top of your head if it is a 12 volt signal?
 

SmokingRocks

Buy it, build it, bash it... Repeat
Joined
Oct 6, 2014
Messages
2,901
Location
Colorado
@sbman are those pages out of the 95-97 FSM?

They are so much better than the OBD1 version I have. Mine shows everything yours does but doesn't show what happens to the circuit in once received by the ECU's.
Capture.JPG
 

blkprj80

SILVER Star
Joined
Jun 20, 2012
Messages
1,919
Location
Lafayette, CO
@sbman nailed it. If you cut the wire named engine temp cut relay, and wire a DPST switch such that it will either tie the ECU input to +12V Ign, or complete the circuit normally, it will idle up however much it normally does w/ AC. But, that doesn't seem to be much, like 750 vs 650 maybe?

You can also cut a stick a bit longer than your current seat to pedal distance. For idle up, place stick and move seat forward just right. I've done this with mine for faster warmup and during break in.

This did NOT work with my 09 GMC though. Drive by wire sees it as "acceleration" and not just throttle position. You either have idle or climbing throttle. The throttle climbs to way beyond what I was wanting (about 2K rpm), so I gave up. :(

Anyhow, if you use the stick and the seat method, and you plan to use it as a cruise control, cut the stick plenty long so you can pin the throttle to the mat without making your knees hit the dash. :flipoff2:o_O
 
Last edited:
Joined
Apr 19, 2015
Messages
1,174
Location
Ramona, CA
@sbman nailed it. If you cut the wire named engine temp cut relay, and wire a DPST switch such that it will either tie the ECU input to +12V Ign, or complete the circuit normally, it will idle up however much it normally does w/ AC. But, that doesn't seem to be much, like 750 vs 650 maybe?

You can also cut a stick a bit longer than your current seat to pedal distance. For idle up, place stick and move seat forward just right. I've done this with mine for faster warmup and during break in.

This did NOT work with my 09 GMC though. Drive by wire sees it as "acceleration" and not just throttle position. You either have idle or climbing throttle. The throttle climbs to way beyond what I was wanting (about 2K rpm), so I gave up. :(

Anyhow, if you use the stick and the seat method, and you plan to use it as a cruise control, cut the stick plenty long so you can pin the throttle to the mat without making your knees hit the dash. :flipoff2:o_O
That's great! I used to use a plastic water bottle as cruise control in my '88 toyota pickup 4WD with the 22RE and 5 speed. It would max out about 75 on level ground with 31" tires. Just kick it out of the way to 'cancel' cruise control. I used an empty one so I could smash it if I had any interference issues.
 

SmokingRocks

Buy it, build it, bash it... Repeat
Joined
Oct 6, 2014
Messages
2,901
Location
Colorado
Ya I've used a funnel to pedal setup before. While I appreciate the inpu I want a permanent professional solution not a half assed bandaid.
 
Top Bottom