Whats the acceptable range for the IAC to be bouncing around?
07-06-2009, 08:47 PM
#2
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The IAC can range from 0 to 160 counts, iirc.
If it's bouncing between 50-60, you're okay. If memory serves, people used to set the idle stop screw so that the IAC was around 35~40 counts at idle, ideally. The really important thing is not to have it bottom or max out -- to the point where the IAC is no longer controlling idle engine speed.
If it's bouncing between 50-60, you're okay. If memory serves, people used to set the idle stop screw so that the IAC was around 35~40 counts at idle, ideally. The really important thing is not to have it bottom or max out -- to the point where the IAC is no longer controlling idle engine speed.
07-07-2009, 01:20 PM
#3
The IAC can range from 0 to 160 counts, iirc.
If it's bouncing between 50-60, you're okay. If memory serves, people used to set the idle stop screw so that the IAC was around 35~40 counts at idle, ideally. The really important thing is not to have it bottom or max out -- to the point where the IAC is no longer controlling idle engine speed.
If it's bouncing between 50-60, you're okay. If memory serves, people used to set the idle stop screw so that the IAC was around 35~40 counts at idle, ideally. The really important thing is not to have it bottom or max out -- to the point where the IAC is no longer controlling idle engine speed.
You wouldn't happen to know the ideal TPS voltage at 0% throttle and WOT?
07-07-2009, 05:09 PM
#7
TECH Veteran
Stock IAC steps are in the 20-30 range at hot idle. Big cams and other mods are going to affect it (normally make them higher as it tries to bring in more air to meet the idle RPM). If the readings go too high, then the IAC has trouble being able to adjust idle, because there is a limit as to how much air it can let in. Cracking the throttle blades open slightly (you'll have to re-adjusting the TPS) can bring them back down (note, this is only for modified engines).
.55v-.65v is the sweet spot for TPS voltage at 0% throttle. 5v is the max it can go (usually goes to 4.7-8v). It does not really matter too much as long as the computer sees it at 100%.
The computer looks at the 0% throtte TPS voltage every time you turn the key on. As long as it is in the range of .3v-.9v, it will set the TPS reading at 0%. So, really, anything in between the voltage range should be ok, but the sweet spot listed above is right in the middle to avoid any potential issues.
.55v-.65v is the sweet spot for TPS voltage at 0% throttle. 5v is the max it can go (usually goes to 4.7-8v). It does not really matter too much as long as the computer sees it at 100%.
The computer looks at the 0% throtte TPS voltage every time you turn the key on. As long as it is in the range of .3v-.9v, it will set the TPS reading at 0%. So, really, anything in between the voltage range should be ok, but the sweet spot listed above is right in the middle to avoid any potential issues.
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07-07-2009, 07:22 PM
#9
Stock IAC steps are in the 20-30 range at hot idle. Big cams and other mods are going to affect it (normally make them higher as it tries to bring in more air to meet the idle RPM). If the readings go too high, then the IAC has trouble being able to adjust idle, because there is a limit as to how much air it can let in. Cracking the throttle blades open slightly (you'll have to re-adjusting the TPS) can bring them back down (note, this is only for modified engines).
.55v-.65v is the sweet spot for TPS voltage at 0% throttle. 5v is the max it can go (usually goes to 4.7-8v). It does not really matter too much as long as the computer sees it at 100%.
The computer looks at the 0% throtte TPS voltage every time you turn the key on. As long as it is in the range of .3v-.9v, it will set the TPS reading at 0%. So, really, anything in between the voltage range should be ok, but the sweet spot listed above is right in the middle to avoid any potential issues.
.55v-.65v is the sweet spot for TPS voltage at 0% throttle. 5v is the max it can go (usually goes to 4.7-8v). It does not really matter too much as long as the computer sees it at 100%.
The computer looks at the 0% throtte TPS voltage every time you turn the key on. As long as it is in the range of .3v-.9v, it will set the TPS reading at 0%. So, really, anything in between the voltage range should be ok, but the sweet spot listed above is right in the middle to avoid any potential issues.
07-08-2009, 10:53 AM
#12
TECH Veteran
07-08-2009, 12:39 PM
#14
After further review. At hot idle it is bouncing between 45-48 points or so. I am going to leave it alone.
The only occasional glitch I get is when slowing down to a stop and puching in the clutch, the RPM's will occasional drop to around 700-800 RPM or so then promptly climb back up to idle RPM of 800. I was told that this is NOT releated to the IAC or TPS. Maybe I am wrong???
The only occasional glitch I get is when slowing down to a stop and puching in the clutch, the RPM's will occasional drop to around 700-800 RPM or so then promptly climb back up to idle RPM of 800. I was told that this is NOT releated to the IAC or TPS. Maybe I am wrong???
07-08-2009, 03:03 PM
#15
Iac follower vs mph table in tuner cats might help you out.
Are you engine braking right before this little problem happens, is it in dfco right before? What does it look like in a log if you can get it to happen?
You need to figure out the exact circumstances that it occurs, is it a particular mph or gear or what. Then look on the log at timing and what the iac counts are doing and at what mph.
Are you engine braking right before this little problem happens, is it in dfco right before? What does it look like in a log if you can get it to happen?
You need to figure out the exact circumstances that it occurs, is it a particular mph or gear or what. Then look on the log at timing and what the iac counts are doing and at what mph.
07-08-2009, 03:35 PM
#16
Iac follower vs mph table in tuner cats might help you out.
Are you engine braking right before this little problem happens, is it in dfco right before? What does it look like in a log if you can get it to happen?
You need to figure out the exact circumstances that it occurs, is it a particular mph or gear or what. Then look on the log at timing and what the iac counts are doing and at what mph.
Are you engine braking right before this little problem happens, is it in dfco right before? What does it look like in a log if you can get it to happen?
You need to figure out the exact circumstances that it occurs, is it a particular mph or gear or what. Then look on the log at timing and what the iac counts are doing and at what mph.
Good questions. Dunno?
Will try to get some answers ASAP.
Thanks
07-08-2009, 04:45 PM
#17
After further review. At hot idle it is bouncing between 45-48 points or so. I am going to leave it alone.
The only occasional glitch I get is when slowing down to a stop and puching in the clutch, the RPM's will occasional drop to around 700-800 RPM or so then promptly climb back up to idle RPM of 800. I was told that this is NOT releated to the IAC or TPS. Maybe I am wrong???
The only occasional glitch I get is when slowing down to a stop and puching in the clutch, the RPM's will occasional drop to around 700-800 RPM or so then promptly climb back up to idle RPM of 800. I was told that this is NOT releated to the IAC or TPS. Maybe I am wrong???
07-08-2009, 06:39 PM
#18
To answer the question posed by WS6.
It did it today backing into the garage and NOT engine braking. Dropped then quickly recovered.
Is this th DFCO paramenter, maybe?
07-09-2009, 01:29 AM
#19
DFCO is fuel cutoff like during engine braking, ie injectors dead closed. I thought maybe it was a blending problem and not relighting the engine at the right time and letting the revs drop doesn't seem to be the case here. There is a bunch to setting up DFCO that I refuse to type out it's got a whole boatload of settings, knock yourself out.
It could also be a timing issue, when you step on the clutch the load is going to change pretty drastically and that will affect both the map and the rpm and change the timing. Which will have a huge effect on a relatively unloaded engine.
If adjusting the tb blades fixes it it was very likely a throttle follower table issue (iac vs mph). Its also why some manual cars seem to just stay stuck at 2000rpm when on the clutch pedal rolling and then calm down after a bit at idle or approaching a dead stop.
I don't worry about the range its in as long as its 20 from either of the extremes at all times. I think being higher lets it have better control of the idle because 1 step isn't such a drastic % change. The factory sets it the way they do to prevent stalling since the motor only moves so fast.
Your A/C isn't on during any of this is it, the A/C compressor engaging will sometimes cause a sag in the rpm.
Just some food for thought and things to look at.
It could also be a timing issue, when you step on the clutch the load is going to change pretty drastically and that will affect both the map and the rpm and change the timing. Which will have a huge effect on a relatively unloaded engine.
If adjusting the tb blades fixes it it was very likely a throttle follower table issue (iac vs mph). Its also why some manual cars seem to just stay stuck at 2000rpm when on the clutch pedal rolling and then calm down after a bit at idle or approaching a dead stop.
I don't worry about the range its in as long as its 20 from either of the extremes at all times. I think being higher lets it have better control of the idle because 1 step isn't such a drastic % change. The factory sets it the way they do to prevent stalling since the motor only moves so fast.
Your A/C isn't on during any of this is it, the A/C compressor engaging will sometimes cause a sag in the rpm.
Just some food for thought and things to look at.
07-09-2009, 11:07 AM
#20
FWIW my undersdtanding is
TPS settings with blades closed is .67 vdc and 4.5 vdc full open
IAC counts 32 with engine at operating temp
YMMV :-)
My scan software shows "desired IAC" count which is 32...may be what the tuner wants to see
As mentioned the IAC is 0-160 so if it is at a base setting to high or low of 30ish than the PCM can not command it to adjust enough one way or the other to keep the idle right. When the AC kicks on or the PS is on more during a turn, etc. This puts a larger load on motor and PCM sends signal to IAC so idle remains constant at whatever it is set at. For many stroker and or heads/cam cars idle is "around" 825 RPM vs the lower 700-750 range on stock motors
I might guess that if IAC was in the 40's or higher and owner experiences a delay or slight idle surge before it settles that the travel the IAC is trying to accomplish is more than desired thus causeing the motor to "stumble/surge" for a moment before the IAC can catch up
TPS settings with blades closed is .67 vdc and 4.5 vdc full open
IAC counts 32 with engine at operating temp
YMMV :-)
My scan software shows "desired IAC" count which is 32...may be what the tuner wants to see
As mentioned the IAC is 0-160 so if it is at a base setting to high or low of 30ish than the PCM can not command it to adjust enough one way or the other to keep the idle right. When the AC kicks on or the PS is on more during a turn, etc. This puts a larger load on motor and PCM sends signal to IAC so idle remains constant at whatever it is set at. For many stroker and or heads/cam cars idle is "around" 825 RPM vs the lower 700-750 range on stock motors
I might guess that if IAC was in the 40's or higher and owner experiences a delay or slight idle surge before it settles that the travel the IAC is trying to accomplish is more than desired thus causeing the motor to "stumble/surge" for a moment before the IAC can catch up
