Not yet, I changed the IAC and reset the ECM and nothing. Still doing the same thing. Some people are saying that I need to get it tune like with an SCT or HP Tuner. I can't believe that the issue would be a tune. The engine idle fine pre-engine build and after the engine was build?
Engine Won't Stay Idling?
- Thread starter fe4snake
- Start date
Your (2) main electronic Throttle "controls" are the IAC which opens and closes to provide a bypass for your throttle body. (Some like to call the IAC a Stepper Motor. 
; and the TPS.
If your throttle body is almost completely closed (at idle), your IAC will provide enough bypass-air for the engine behind the throttle body blade(s) to keep the engine idling at a consistent speed to compensate for variable-load items like Power steering Pumps, Alternators, the AC compressor clicking on and off, whether you are in Park or Drive, etc. The IAC moves a very small amount back and forth as may be required for the given engine loads to keep the engine at a steady rpm.
The Throttle Position Sensor is just that a Sensor that is a simple Rheostat for the ECU (Main computer) to know the position of the Throttle so it can adjust fuel and ignition timing accordingly. If the TPS goes bad, the idle may flair and/or take it's time coming back down to normal because it is sending the wrong info to the ECU. The ECU in turn sends the wrong data out to the rest of the players.
Beyond those 2, there is also a MAP (Manifold Absolute Pressure Sensor) that uses a piezo membrane to detect Barometric Pressure. This data is sent to the ECU so it can adjust fuel flow and timing appropriate for the other conditions (coolant temperature, Throttle Position, knock-sensor feedback (after 2004), IAT, current engine load, etc.)
All of these things work seamlessly together (almost all of the time) to let us enjoy our trucks.
The IAC and to a lesser degree the TPS, are the 2 controlling idle the most, kinda-sorta.
If you know these 2 to be in fine operating condition, start looking for non-electronic things like if the hose is firmly connected behind your throttle body (the one that points straight down). Also check other vacuum hoses that may be cracked or disconnected that could be messing with the orchestra.
; and the TPS.If your throttle body is almost completely closed (at idle), your IAC will provide enough bypass-air for the engine behind the throttle body blade(s) to keep the engine idling at a consistent speed to compensate for variable-load items like Power steering Pumps, Alternators, the AC compressor clicking on and off, whether you are in Park or Drive, etc. The IAC moves a very small amount back and forth as may be required for the given engine loads to keep the engine at a steady rpm.
The Throttle Position Sensor is just that a Sensor that is a simple Rheostat for the ECU (Main computer) to know the position of the Throttle so it can adjust fuel and ignition timing accordingly. If the TPS goes bad, the idle may flair and/or take it's time coming back down to normal because it is sending the wrong info to the ECU. The ECU in turn sends the wrong data out to the rest of the players.
Beyond those 2, there is also a MAP (Manifold Absolute Pressure Sensor) that uses a piezo membrane to detect Barometric Pressure. This data is sent to the ECU so it can adjust fuel flow and timing appropriate for the other conditions (coolant temperature, Throttle Position, knock-sensor feedback (after 2004), IAT, current engine load, etc.)
All of these things work seamlessly together (almost all of the time) to let us enjoy our trucks.
The IAC and to a lesser degree the TPS, are the 2 controlling idle the most, kinda-sorta.
If you know these 2 to be in fine operating condition, start looking for non-electronic things like if the hose is firmly connected behind your throttle body (the one that points straight down). Also check other vacuum hoses that may be cracked or disconnected that could be messing with the orchestra.
Last edited:
AMS3
Full Access Member
You Da Man Ronnie!!!Your (2) main electronic Throttle "controls" are the IAC which opens and closes to provide a bypass for your throttle body. (Some like to call the IAC a Stepper Motor.
If your throttle body is almost completely closed (at idle), your IAC will provide enough bypass-air for the engine behind the throttle body blade(s) to keep the engine idling at a consistent speed to compensate for variable-load items like Power steering Pumps, Alternators, the AC compressor clicking on and off, whether you are in Park or Drive, etc. The IAC moves a very small amount back and forth as may be required for the given engine loads to keep the engine at a steady rpm.
The Throttle Position Sensor is just that a Sensor that is a simple Rheostat for the ECU (Main computer) to know the position of the Throttle so it can adjust fuel and ignition timing accordingly. If the TPS goes bad, the idle may flair and/or take it's time coming back down to normal because it is sending the wrong info to the ECU. The ECU in turn sends the wrong data out to the rest of the players.
Beyond those 2, there is also a MAP (Manifold Absolute Pressure Sensor) that uses a piezo membrane to detect Barometric Pressure. This data is sent to the ECU so it can adjust fuel flow and timing appropriate for the other conditions (coolant temperature, Throttle Position, knock-sensor feedback (after 2004), IAT, current engine load, etc.)
All of these things work seamlessly together (almost all of the time) to let us enjoy our trucks.
The IAC and to a lesser degree the TPS, are the 2 controlling idle the most, kinda-sorta.
If you know these 2 to be in fine operating condition, start looking for non-electronic things like if the hose is firmly connected behind your throttle body (the one that points straight down). Also check other vacuum hoses that may be cracked or disconnected that could be messing with the orchestra.
Curious to know what's wrong with buddie's truck...
you should do a smoke check to find the vacuum leak.....
beastmode1
Full Access Member
I concur with Ronnie on this.The ECU can lose count of adaptive control of the IAC which is controlled in incremental steps.
The IAC is a Stepper Motor.
Resetting the ecu with the battery cable "trick" will return it to the tuned baseline.
Best to ask for an IAC at a Parts Department though, so they don't refer you to a company that sells Escalators.
beastmode1
Full Access Member
I used Carb Cleaner on mine and it went away and I had to clean the gunk out. Remember to spray on a clean cloth and wipe gently.
beastmode1
Full Access Member
Kiwi that is motor lingo lol!!!!All these IAC's and ECU's and ABC's EQC OBE sheet I am losin' the plot. All sounds like Swahili to me. Does anyone hear speak English LOL
beastmode1
Full Access Member
Hey Kiwi you are singing to the choir too much mambo jambo lol!!!All these IAC's and ECU's and ABC's EQC OBE sheet I am losin' the plot. All sounds like Swahili to me. Does anyone hear speak English LOL
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