What controls the idle on...

[nycstev]

these trucks? I know the set screw does but does the PCM do this also?
How does it work?

 

[bigike]

This is a speed density system.

The pcm is set up on a set curve for air temp and throttle position and rpm to regulate the fuel air mixture.

The Idle screw adjusts hard idle but I believe the pcm will control it alittle with the fuel, although the pcm can't adjust air. Thats your foot.

 

[ACE]

The pcm acctuly does controll the air via the IAC (idle air control) valve, it is located in or directly behind the throttle body, and is a small stepper motor that bypasses a small amount of air around the throttle plate...

 

[bigike]

Idle air control motor ............. damn now I remember those would alway F up on the 5.0's!

 

[belgiumbarry]

could it be the IAC Steve? that one is now on our ROE mounted on the block with the tube going to the air filter... Perhaps by-passing just a bit to much air :dontknow: :dontknow:

Will check the inside , have seen the pen of the IAC has a schaped head as typical for a regulator...

So inside shape and depth should be the same on stock manifold and ROE...

Also i think the big TB leaks more air then the stock one seeing the play around the blade holding against a light... :dontknow:

Mine stalls sometimes around 1500 revs to come slow down to 750...

 

[SERPENT]

Have exactly the same problem as Barry. Idle slow to come down from 1500 rpm. Have replaced the TPS and the Idle Air Controller and have brought the fuel pressure to 50 psi with vac off at idle. No fix there. Spoke to Justin yesterday--he had similar problem and took off throttle body and readjusted blade. Problem solved apparently.

 

[bigike]

Venom Powers did the same thing.

 

[belgiumbarry]

Have exactly the same problem as Barry. Idle slow to come down from 1500 rpm. Have replaced the TPS and the Idle Air Controller and have brought the fuel pressure to 50 psi with vac off at idle. No fix there. Spoke to Justin yesterday--he had similar problem and took off throttle body and readjusted blade. Problem solved apparently.

The IAC have indeed exactly the same manner of mounting on our ROE.

Compared to the stock blades our big blade has alot more play inside... i see light around were on the stock it's almost complete closed... Could be the problem that still to much air is passing a closed blade... but when it's perfect aligned... cannot think what to readjust... :dontknow: :dontknow: and even if so ... let's assume to much air still passing the blade... is it then the PCM with info from the TPS that reduces (slowly) the idle from 1500 to 750 revs :dontknow:

 

[WOT]

Typically, the PCM commands a specific number of "steps" in the IAC as it's initial guess - meaning that when you first fire up the motor or when coming down from cruise rpm, etc., it may command say, 75 steps. That will correspond to a certain position of the IAC. This is the PCM's best guess on where the IAC's pintle position should be for correct idle speed (it also prevents backfire on sudden throttle chop, and helps reduce certain types of emissions, but let's ignore all that). Once the the PCM has had a chance to watch the motor rpm it will make an adjustment to get to the proper idle speed. If the throttle body is opened more via the set screw (or if the TB is bigger and flows more air at idle), the engine will hang at a higher rpm for a while until the PCM decides to lower the "steps" in the IAC.

The fix for this is to either back off the set screw or to chance the program's default steps vs. vehicle speed table to compensate for this.

Ever notice how when cruising down the highway, sometimes it feels like you are just barely having to push the accelerator pedal when going from cruising to costing to back to cruising? That is because at highway speed, the PCM holds the IAC open a little to make the throttle on-off transition seem smoother. It makes driving the truck easier, such as with a manual transmission you don't have to push in the clutch immediately when backing off the throttle at speed to prevent jerking, or in the case of an automatic, it doesn't have to unlock the converter as quick to prevent jerking a bit on throttle lift at speed (on sudden throttle lift, it holds the IAC open for a specified number of miliseconds until the converter has a chance to unlock, and then it backs down).

Anyway, that's how the IAC vs. engine speed vs vehicle speed works.

 

[BigRed460]

Venom Powers did the same thing.

We brought it to my shop and fix it, the tps was out of adjustment... The position of it sets the idle

 

[mauiSRT/10]

Typically, the PCM commands a specific number of "steps" in the IAC as it's initial guess - meaning that when you first fire up the motor or when coming down from cruise rpm, etc., it may command say, 75 steps. That will correspond to a certain position of the IAC. This is the PCM's best guess on where the IAC's pintle position should be for correct idle speed (it also prevents backfire on sudden throttle chop, and helps reduce certain types of emissions, but let's ignore all that). Once the the PCM has had a chance to watch the motor rpm it will make an adjustment to get to the proper idle speed. If the throttle body is opened more via the set screw (or if the TB is bigger and flows more air at idle), the engine will hang at a higher rpm for a while until the PCM decides to lower the "steps" in the IAC.

The fix for this is to either back off the set screw or to chance the program's default steps vs. vehicle speed table to compensate for this.

Ever notice how when cruising down the highway, sometimes it feels like you are just barely having to push the accelerator pedal when going from cruising to costing to back to cruising? That is because at highway speed, the PCM holds the IAC open a little to make the throttle on-off transition seem smoother. It makes driving the truck easier, such as with a manual transmission you don't have to push in the clutch immediately when backing off the throttle at speed to prevent jerking, or in the case of an automatic, it doesn't have to unlock the converter as quick to prevent jerking a bit on throttle lift at speed (on sudden throttle lift, it holds the IAC open for a specified number of miliseconds until the converter has a chance to unlock, and then it backs down).

Anyway, that's how the IAC vs. engine speed vs vehicle speed works.

Nice post WOT.

patrick

 

[belgiumbarry]

Typically, the PCM commands a specific number of "steps" in the IAC as it's initial guess - meaning that when you first fire up the motor or when coming down from cruise rpm, etc., it may command say, 75 steps. That will correspond to a certain position of the IAC. This is the PCM's best guess on where the IAC's pintle position should be for correct idle speed (it also prevents backfire on sudden throttle chop, and helps reduce certain types of emissions, but let's ignore all that). Once the the PCM has had a chance to watch the motor rpm it will make an adjustment to get to the proper idle speed. If the throttle body is opened more via the set screw (or if the TB is bigger and flows more air at idle), the engine will hang at a higher rpm for a while until the PCM decides to lower the "steps" in the IAC.

The fix for this is to either back off the set screw or to chance the program's default steps vs. vehicle speed table to compensate for this.

Ever notice how when cruising down the highway, sometimes it feels like you are just barely having to push the accelerator pedal when going from cruising to costing to back to cruising? That is because at highway speed, the PCM holds the IAC open a little to make the throttle on-off transition seem smoother. It makes driving the truck easier, such as with a manual transmission you don't have to push in the clutch immediately when backing off the throttle at speed to prevent jerking, or in the case of an automatic, it doesn't have to unlock the converter as quick to prevent jerking a bit on throttle lift at speed (on sudden throttle lift, it holds the IAC open for a specified number of miliseconds until the converter has a chance to unlock, and then it backs down).

Anyway, that's how the IAC vs. engine speed vs vehicle speed works.

great write WOT :rock: :rock: ....but Xmetal warn us on instructions NOT to back off the set screw !!! :dontknow:

 

[belgiumbarry]

great info from ROE RACING :rock: :rock: :rock:

Hallo, those guys are way profesional :rock: got reply within a hour with my question.. chapeau ROE :rock: and THANKS !



Hello,



Thank you for the kind words regarding our products.



We have never experienced the problem you are describing. However, we have never installed an Xmetal throttle body either. I have listed a reset procedure below. Please follow the instructions as listed and see if that helps the stalling problem. If it does not, you may want to try installing your stock throttle body to see if that helps.



For all 2004-2006 SRT-10 Ram trucks with a Roe Racing supercharger kit.



This procedure must be followed if the battery is ever disconnected or drained to the point of the truck not starting.



1. Disconnect all three PCM connectors for about 10 minutes. By doing this, you are erasing the PCM adaptive memory. The PCM is located on the firewall directly above and behind the passenger side front wheel.

2. Disconnect the TPS (throttle position sensor) on the driver’s side of the throttle body. Ensure all wire connections are correct.

3. Disconnect the IAC (idle air control motor) on the air plenum located on the passenger side directly behind the air filter. Ensure all wire connections are correct.

4. With the PCM disconnected, make sure the throttle cable and throttle linkage is adjusted properly for wide-open throttle. The driver’s floor mat should be removed as it can inhibit accelerator pedal travel.

5. After wide-open throttle is verified or adjusted, reconnect the PCM, TPS and IAC connectors after 10 minutes has elapsed from the start of this procedure.

6. Turn the key to the "on" position, but DO NOT start the engine.

7. With the drivers floor mat out of the truck, slowly press the accelerator to full throttle, then repeat. By doing this, you are showing the TPS (throttle position sensor) full throttle. Without this information in the PCM, it will not correctly calculate how to make the engine run properly.

8. Turn the key off then start the truck without touching the accelerator.

9. Let the engine idle for approximately 2-3 minutes.

10. After idling, drive easy, then progressively harder over the course of about 10-20 minutes.

11. The truck will drive differently during the first 20-40 miles because the PCM is learning the new adaptives.



To get the signal for the A/F gauge, tap into one of the wires coming from the O2 sensor going to the VEC3.



Regards,

Dave Venski, General Manager, Roe Racing USA

1768 Wildwood Road, Green Cove Springs, FL 32043

904-529-1219 ex. 2#

www.roeracing.com