Disconnected Idle Air Control - for lower RPM after a cold start

[Lazarus]

You could always pull the plug on the Idle speed control valve at around 1000 rpm. You would have to feather the engine to keep it running when cold but it does save petro.

[RH77]

Originally Posted by Lazarus

You could always pull the plug on the Idle speed control valve at around 1000 rpm. You would have to feather the engine to keep it running when cold but it does save petro.

Hmmm -- that's actually a great idea. On cold starts, it motors along at 2K (forced into 2nd, it just kinda goes without any pedal). I wonder if it would freak-out the ECU...

Good thinking, tho

RH77

[Lazarus]

Originally Posted by RH77

Hmmm -- that's actually a great idea. On cold starts, it motors along at 2K (forced into 2nd, it just kinda goes without any pedal). I wonder if it would freak-out the ECU...

Good thinking, tho

RH77

It almost like having a block heater with the difference with and without. Our winter or pretty mild here so it not that big of deal. I run it like that all year round. It does make it a car that only you can drive though. You have to feather the throttle with one foot and brake with the other or it will die until it gets warm up. Which as cold as it is there might not make it worth it but the ECU in the woo is fine with it. Good luck.

[RH77]

Well, that was "Interesting"...

I disconnected the Idle Air Control to see what would happen on a cold start.

As expected, it took some feathering of the throttle to keep it running -- but after it warmed-up, it still required the input.

Some notable notations:

• High Idle disappears (good)
• (All the following items occurs, including after warmup...)
• When slowing to a stop, the car stalls in Drive before stopping (it's a nice smooth shutdown -- you don't even know it until the charge light comes on and the steering gets stiff)
• Vehicle stalls in Neutral (easy engine cut -- just shift to "N")
• Engine Code Thrown - P1503 IACV Malfunction
• Unknown operation: closed or open loop (used datalogger instead of SG-II)

Side note: the A/T version of this vehicle has a "Fast Idle Thermo Valve", which is a coolant operated wax plunger that keeps the idle up when cold (downstream of the IACV). This might be the target device, but has no "quick disconnect" -- it would require looping the coolant line back into itself (and no easy way to switch it).

Operation: What's fun, is that you can coast down at 400 RPM and keep an eye on things to keep from stalling, while in Drive -- and just give it a little throttle and off you go, or downshift to keep the engine alive...

To continue with this experiment, a couple things need confirmed:
- Is the low RPM operation potentially reducing the amount of oil and/or transmission fluid being pumped (down to a dangerous level)? It doesn't lug (so no concern there).
- I have a switch that I can wire into the sensor, so I could have more control when the vehicle is warm. Not being well-versed with feathering the throttle, some hard transmission engagements occurred at lights.
- Is this saving fuel, or could the ECU be compensating for the error? The SG can answer that soon...

I have the shop manual which noted the IACV circuit is involved in a complex feedback system that's fed to the ECU and determines idle among a bunch of other things. It didn't go into detail on the specifics of the ECU's logarithms in this case, but instead circuit and device troubleshooting, so

Any thoughts?

RH77

[Lazarus]

Originally Posted by RH77

Well, that was "Interesting"...

I disconnected the Idle Air Control to see what would happen on a cold start.

As expected, it took some feathering of the throttle to keep it running -- but after it warmed-up, it still required the input.

Some notable notations:

• High Idle disappears (good)
• (All the following items occurs, including after warmup...)
• When slowing to a stop, the car stalls in Drive before stopping (it's a nice smooth shutdown -- you don't even know it until the charge light comes on and the steering gets stiff)
• Vehicle stalls in Neutral (easy engine cut -- just shift to "N")
• Engine Code Thrown - P1503 IACV Malfunction
• Unknown operation: closed or open loop (used datalogger instead of SG-II)

Side note: the A/T version of this vehicle has a "Fast Idle Thermo Valve", which is a coolant operated wax plunger that keeps the idle up when cold (downstream of the IACV). This might be the target device, but has no "quick disconnect" -- it would require looping the coolant line back into itself (and no easy way to switch it).

Operation: What's fun, is that you can coast down at 400 RPM and keep an eye on things to keep from stalling, while in Drive -- and just give it a little throttle and off you go, or downshift to keep the engine alive...

To continue with this experiment, a couple things need confirmed:
- Is the low RPM operation potentially reducing the amount of oil and/or transmission fluid being pumped (down to a dangerous level)? It doesn't lug (so no concern there).
- I have a switch that I can wire into the sensor, so I could have more control when the vehicle is warm. Not being well-versed with feathering the throttle, some hard transmission engagements occurred at lights.
- Is this saving fuel, or could the ECU be compensating for the error? The SG can answer that soon...

I have the shop manual which noted the IACV circuit is involved in a complex feedback system that's fed to the ECU and determines idle among a bunch of other things. It didn't go into detail on the specifics of the ECU's logarithms in this case, but instead circuit and device troubleshooting, so

Any thoughts?

RH77

Rick,
Did you warm up the car and with it running at the RPM you want disconnect it? If not it will show those symptoms. I get the CEL light for low idle about 1 a month. Just use the SG and clear it.

[RH77]

Originally Posted by Lazarus

Rick,
Did you warm up the car and with it running at the RPM you want disconnect it? If not it will show those symptoms. I get the CEL light for low idle about 1 a month. Just use the SG and clear it.

No, it was a cold start, with the car off. I wondered what you meant by a "1000 RPM set" -- good point.

I'm trying to rationalize the ECU's interpretation -- it must use the last input of RPM and IACV voltage as a baseline, and use those for the ECU's current calcs. How did you come across this, by the way? -- interesting idea...

RH77

[Lazarus]

Originally Posted by RH77

No, it was a cold start, with the car off. I wondered what you meant by a "1000 RPM set" -- good point.

I'm trying to rationalize the ECU's interpretation -- it must use the last input of RPM and IACV voltage as a baseline, and use those for the ECU's current calcs. How did you come across this, by the way? -- interesting idea...

RH77

I think that's the way it works. I believe it was either Larry's or Carlos (picka picka) idea. I just stole it Like to see your results. I got about 5% out of it.

[RH77]

Originally Posted by Lazarus

I think that's the way it works. I believe it was either Larry's or Carlos (picka picka) idea. I just stole it Like to see your results. I got about 5% out of it.

Just after that post last night, I went out and followed the instructions as indicated. No luck. Even at normal operating temp, revved up to 1000 RPM, pulled the IACV, and ka-put.

The ECU is just too involved in the process and is debilitated without it. The next try is to wire it to a switch in the cabin, to have more control over it. I still have that toggle installed from the cylinder deactivation experiment 2 years ago

The lowest I could get the engine to turn was 400 RPM. Does anyone know if this is too low to pump vital fluids (tranny, oil, etc.)??? I can coast-down in top gear in "D" and it just gently dies after 400 R's, or if I downshift to 3rd, it comes back alive (same with feathering of the throttle). Maybe the switch will allow some more creative control over the process.

Side note: it seems to idle fine at 400-500 RPM -- could this be a fuel saver? I tried the A/C and maxed-out the electrical load and it was fine -- no stalls.

RH77

P.S. Thanks for moving the thread -- clogging up the EBH info, off-topic and all

[Lazarus]

Originally Posted by RH77

Just after that post last night, I went out and followed the instructions as indicated. No luck. Even at normal operating temp, revved up to 1000 RPM, pulled the IACV, and ka-put.

The ECU is just too involved in the process and is debilitated without it. The next try is to wire it to a switch in the cabin, to have more control over it. I still have that toggle installed from the cylinder deactivation experiment 2 years ago

The lowest I could get the engine to turn was 400 RPM. Does anyone know if this is too low to pump vital fluids (tranny, oil, etc.)??? I can coast-down in top gear in "D" and it just gently dies after 400 R's, or if I downshift to 3rd, it comes back alive (same with feathering of the throttle). Maybe the switch will allow some more creative control over the process.

Side note: it seems to idle fine at 400-500 RPM -- could this be a fuel saver? I tried the A/C and maxed-out the electrical load and it was fine -- no stalls.

RH77

P.S. Thanks for moving the thread -- clogging up the EBH info, off-topic and all

Does the data logger you have record oil pressure? See who low it is when you're at 500 rpm. I guess when it's that low no idiot lights?

[metroschultz]

Originally Posted by RH77

The lowest I could get the engine to turn was 400 RPM. Does anyone know if this is too low to pump vital fluids (tranny, oil, etc.)??? I can coast-down in top gear in "D" and it just gently dies after 400 R's, or if I downshift to 3rd, it comes back alive (same with feathering of the throttle). Maybe the switch will allow some more creative control over the process.

Side note: it seems to idle fine at 400-500 RPM -- could this be a fuel saver? I tried the A/C and maxed-out the electrical load and it was fine -- no stalls.

RH77

P.S. Thanks for moving the thread -- clogging up the EBH info, off-topic and all

Short Answer, Yes.

Low rpm will still deliver adequate oil distribution to all your vitals in the engine, and in a manual trans.
Caveat to auto owners, most of the autos in passenger cars have a stall speed near ~ 1200 rpm.
This means below 75% or ~ 800 rpm there is not enough fluid pressure in the torque for operation. AND.
below 50% or ~ 600 rpm there won't be enough fluid pressure to lubricate the rotating assembly in the case.
I can't remember which tranny you've got, and they are not all identical. These are just rough numbers.

That Said,
Many newer cars use fuzzy logic in the controls for the engine and follow your particular driving habits to keep the rpm as low as possible at idle.

SOOO

For greater savings, lower idle is better, no idle (EO) is better still.

Since my car is three colors of blue with one black fender, I get many DIRTY looks when I restart at lights. toobad soosad yourdad,
they also hate me when I put in $11.5 at the pump and tell 'em I've been driving for three Weeks.