Cold Start Rough Idle
#11
11-12-2009, 10:22 PM
Champion
use the search function and search "merry christmas" thewre you will find a pdf of the service manual to download it will explain all the codes.
#12
11-13-2009, 12:38 AM
Captain
#14
03-03-2010, 06:07 PM
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I just recently put Fuel Injector Cleaner from STP into my gas tank, and it idles like a champ. Maybe that was an exaggeration, but it does idle much much better. I can still tell when it starts to idle a little rough, but it works itself out now, and does not start to shake the whole cab and sound like it is going to stall.
#15
03-03-2010, 07:15 PM
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Mine does this occasionally. At cold start up it will start up and run fine for like 3 maybe 5 secs then it'll get a lopey type idle(kinda like a heavy cam) Then after idleing lopey for like 7 secs or so it'l correct itself, smooth out and be fine. So its not really an issue at all. The truck runs like a brand new one otherwise... I really wanna know what it is tho!
Like i said, the idle i get is like a Lopey idle.. Any idea's anyone??
Like i said, the idle i get is like a Lopey idle.. Any idea's anyone??
#16
03-04-2010, 12:02 PM
Mine does this occasionally. At cold start up it will start up and run fine for like 3 maybe 5 secs then it'll get a lopey type idle(kinda like a heavy cam) Then after idleing lopey for like 7 secs or so it'l correct itself, smooth out and be fine. So its not really an issue at all. The truck runs like a brand new one otherwise... I really wanna know what it is tho!
Like i said, the idle i get is like a Lopey idle.. Any idea's anyone??
Like i said, the idle i get is like a Lopey idle.. Any idea's anyone??
A key on event is triggered and, the MAP, TPS, CPS data values at the PCM level are used during <KEY ON> mode.
At time of cold startup, the PCM is in open loop mode and, no sensors other than the IAC, ECT and CPS are being used. It's run on static parameters along with running rich. All fuel trims are preset at the program level along with using static parameters for air temp, and flow rates. Again, this is called open loop mode.
IN the PCM program, there is a timer that is counting down ~ three minutes. After which time it reaches zero, the PCM will attempt to switch over into what is called closed loop mode. It will only switch over to CLM when certain sensor requirements are met. Those requirements are:
-ECT has reached it's minimum target value in terms of the corresponding voltage output that correlates to engine coolant temperature. The range of this MIN temp range is from 160-~185°F. The next requirement is the exhaust temperature and last requirement escapes me at current.
Once those target values are satisfied, the program now switches modes to which, all the sensor inputs are enabled thus providing data from all of them. This is when your O2 sensors kick in, your TPS, the IAC now adjusts accordingly along with the MAP, the CKPS is also used in this mode etc etc.
So, if you've got an issue after the three minutes- this is good indication that one of your sensors is faulting or you have a vacuum leak. In this case, it sounds like a possible vacuum leak. Why? If it was a sensor issue, more times than not, the loping persists and does not idle out whereas, a vacuum related issue will be canceled out due to the PCM adjusting the MAP readings to accommodate accordingly. The MAP readings affect the rest of the sensors so, if you've got a vac leak, this will throw the entire system out of whack. As you drive it, the PCM will balance it out.
This is one parameter that is fixed at time of startup and, the PCM is expecting a certain value at the MAP while in closed loop mode. IF it doesn't meet the range, the program adjusts to compensate.
The above is also true to more / lesser degree regarding sensors as well so, same thing applies where, the PCM will relearn, interpolate and self adjust within a given range.
Causes of engine idle loping:
Bad IAC valve out of range condition on motor step MIN / MAX
Faulty TPS - may have a dead spot or, erratic voltage reading
Vacuum- vacuum leak. Run a vac test with engine at normal operating temp. Watch for "bobbing" needle, pulsing, swing hi, swing lo, etc. Haynes describes what to look for adequately enough so, get a manual if you don't have one already.
Timing issue: time related issue will also self - correct over a period of time. The timing is electronically controlled and, if it's out a bit, the PCM will adjust as necessary and within a certain range as well.
Those are the most common root cause modes for engine idle loping.
Regards,
CM
Last edited by cmckenna; 03-04-2010 at 12:03 PM. Reason: Removed double quote
#17
03-04-2010, 05:57 PM
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The reason why it runs fine for 3 minutes and then goes to crap, and then normals out is this:
A key on event is triggered and, the MAP, TPS, CPS data values at the PCM level are used during <KEY ON> mode.
At time of cold startup, the PCM is in open loop mode and, no sensors other than the IAC, ECT and CPS are being used. It's run on static parameters along with running rich. All fuel trims are preset at the program level along with using static parameters for air temp, and flow rates. Again, this is called open loop mode.
IN the PCM program, there is a timer that is counting down ~ three minutes. After which time it reaches zero, the PCM will attempt to switch over into what is called closed loop mode. It will only switch over to CLM when certain sensor requirements are met. Those requirements are:
-ECT has reached it's minimum target value in terms of the corresponding voltage output that correlates to engine coolant temperature. The range of this MIN temp range is from 160-~185°F. The next requirement is the exhaust temperature and last requirement escapes me at current.
Once those target values are satisfied, the program now switches modes to which, all the sensor inputs are enabled thus providing data from all of them. This is when your O2 sensors kick in, your TPS, the IAC now adjusts accordingly along with the MAP, the CKPS is also used in this mode etc etc.
So, if you've got an issue after the three minutes- this is good indication that one of your sensors is faulting or you have a vacuum leak. In this case, it sounds like a possible vacuum leak. Why? If it was a sensor issue, more times than not, the loping persists and does not idle out whereas, a vacuum related issue will be canceled out due to the PCM adjusting the MAP readings to accommodate accordingly. The MAP readings affect the rest of the sensors so, if you've got a vac leak, this will throw the entire system out of whack. As you drive it, the PCM will balance it out.
This is one parameter that is fixed at time of startup and, the PCM is expecting a certain value at the MAP while in closed loop mode. IF it doesn't meet the range, the program adjusts to compensate.
The above is also true to more / lesser degree regarding sensors as well so, same thing applies where, the PCM will relearn, interpolate and self adjust within a given range.
Causes of engine idle loping:
Bad IAC valve out of range condition on motor step MIN / MAX
Faulty TPS - may have a dead spot or, erratic voltage reading
Vacuum- vacuum leak. Run a vac test with engine at normal operating temp. Watch for "bobbing" needle, pulsing, swing hi, swing lo, etc. Haynes describes what to look for adequately enough so, get a manual if you don't have one already.
Timing issue: time related issue will also self - correct over a period of time. The timing is electronically controlled and, if it's out a bit, the PCM will adjust as necessary and within a certain range as well.
Those are the most common root cause modes for engine idle loping.
Regards,
CM
A key on event is triggered and, the MAP, TPS, CPS data values at the PCM level are used during <KEY ON> mode.
At time of cold startup, the PCM is in open loop mode and, no sensors other than the IAC, ECT and CPS are being used. It's run on static parameters along with running rich. All fuel trims are preset at the program level along with using static parameters for air temp, and flow rates. Again, this is called open loop mode.
IN the PCM program, there is a timer that is counting down ~ three minutes. After which time it reaches zero, the PCM will attempt to switch over into what is called closed loop mode. It will only switch over to CLM when certain sensor requirements are met. Those requirements are:
-ECT has reached it's minimum target value in terms of the corresponding voltage output that correlates to engine coolant temperature. The range of this MIN temp range is from 160-~185°F. The next requirement is the exhaust temperature and last requirement escapes me at current.
Once those target values are satisfied, the program now switches modes to which, all the sensor inputs are enabled thus providing data from all of them. This is when your O2 sensors kick in, your TPS, the IAC now adjusts accordingly along with the MAP, the CKPS is also used in this mode etc etc.
So, if you've got an issue after the three minutes- this is good indication that one of your sensors is faulting or you have a vacuum leak. In this case, it sounds like a possible vacuum leak. Why? If it was a sensor issue, more times than not, the loping persists and does not idle out whereas, a vacuum related issue will be canceled out due to the PCM adjusting the MAP readings to accommodate accordingly. The MAP readings affect the rest of the sensors so, if you've got a vac leak, this will throw the entire system out of whack. As you drive it, the PCM will balance it out.
This is one parameter that is fixed at time of startup and, the PCM is expecting a certain value at the MAP while in closed loop mode. IF it doesn't meet the range, the program adjusts to compensate.
The above is also true to more / lesser degree regarding sensors as well so, same thing applies where, the PCM will relearn, interpolate and self adjust within a given range.
Causes of engine idle loping:
Bad IAC valve out of range condition on motor step MIN / MAX
Faulty TPS - may have a dead spot or, erratic voltage reading
Vacuum- vacuum leak. Run a vac test with engine at normal operating temp. Watch for "bobbing" needle, pulsing, swing hi, swing lo, etc. Haynes describes what to look for adequately enough so, get a manual if you don't have one already.
Timing issue: time related issue will also self - correct over a period of time. The timing is electronically controlled and, if it's out a bit, the PCM will adjust as necessary and within a certain range as well.
Those are the most common root cause modes for engine idle loping.
Regards,
CM
And it does this occasionally. Not all the time.
#18
03-04-2010, 06:00 PM
Checked vacuum
My vacuum reads 16 to 17, and it is steady until it starts it's "episode." I started it cold and it warmed up with just a hint of the loping problem, but I let it cool down 15 minutes and started it again and it would have died if I didn't open the throttle. I noticed on my antique vacuum gauge that 15 to 17 inches of vacuum shows "Late Ignition Timing." Could that be the crank sensor? If so, do you know what timing should be on this warm-up. I have watched it in the past on my scanner and I seem to remember it changing a lot.
The late timing would explain the times it didn't want to move out normally from a stop.
The late timing would explain the times it didn't want to move out normally from a stop.
#19
03-05-2010, 08:48 AM
My vacuum reads 16 to 17, and it is steady until it starts it's "episode." I started it cold and it warmed up with just a hint of the loping problem, but I let it cool down 15 minutes and started it again and it would have died if I didn't open the throttle. I noticed on my antique vacuum gauge that 15 to 17 inches of vacuum shows "Late Ignition Timing." Could that be the crank sensor? If so, do you know what timing should be on this warm-up. I have watched it in the past on my scanner and I seem to remember it changing a lot.
The late timing would explain the times it didn't want to move out normally from a stop.
The late timing would explain the times it didn't want to move out normally from a stop.
I would remove and replace it along with removing your TB and cleaning that as well. This is the one of the most common issue- sticking IAC valve. What's most likely happening is this.
When you start it, the PCM is programmed to preset the IAC to x-amount gap between the plunger and the bore opening. If that's sticking, binding, has lots of carbon build up, or, the motor control is shot, it causes loping or stalling.
When you are driving, the throttle plates open thus allowing air into the intake. Meanwhile, the IAC valve closes.
During taking your foot off the gas, the plates close and the IAC is supposed to open to allow air into the intake. IN your case, I believe your IAC is sticking thus the reason why to keep your foot on the gas. IN doing this, it allows air to enter and prevents it from choking out / stalling.
Hope that helps.
CM
#20
03-05-2010, 08:56 AM
If it's doing it now, it's most likely going to get worse over time. I would remove and at least check your IAC assy. Also, check the condition of your TB at the IAC ports. This is the most common cause of what you describe.
What is most likely happening is this:
When you turn the vehicle on, the IAC is supposed to move to a preset gap and, if it's sticking or binding- it will not open the correct amount initially. After a few seconds, the valve moves and it's now getting the correct amount of air thus fixing the issue.
Check the IAC assy for sure and clean the TB ports while your at it.
CM