Weird idle problem when putting truck in neutral coming to stops.
#1
Weird idle problem when putting truck in neutral coming to stops.
i replaced my bad ECT sensor yesterday which cured my hesitation problem while the first few minutes of driving my truck cold.
i have always had a sticky idle problem. like when coming to stops, the idle will stick at like 1500 and then drop to like 700-1000.
in the last week, i have noticed that when driving and coasting to stops, whenever i put the truck in neutral, the tach jumps up to like 1500 and stays there, and eventually drops.
this happens more at cold driving but does happen sometimes when truck is warmed up.
you weould think when putting the tranny in neutral or coming to stops, the tach would drop to 700.
any ideas, i am getting no codes from my scanner.....a bad MAF or TPS or IAC would throw a code, correct?
oh yeah, also when shifting, it seems like the rpms jump slightly when tranny is put into next gear.
?????
i have always had a sticky idle problem. like when coming to stops, the idle will stick at like 1500 and then drop to like 700-1000.
in the last week, i have noticed that when driving and coasting to stops, whenever i put the truck in neutral, the tach jumps up to like 1500 and stays there, and eventually drops.
this happens more at cold driving but does happen sometimes when truck is warmed up.
you weould think when putting the tranny in neutral or coming to stops, the tach would drop to 700.
any ideas, i am getting no codes from my scanner.....a bad MAF or TPS or IAC would throw a code, correct?
oh yeah, also when shifting, it seems like the rpms jump slightly when tranny is put into next gear.
?????
Last edited by Jeremy102579; 03-19-2007 at 04:46 AM.
#3
#6
If the RPM is hanging at 1000~1500 while the truck is still rolling, that may be normal.
If the engine is up to operating temperature and it is hanging above curb idle when the truck is stopped, there are 3 likely causes:
the Idle Air Controller is sticking; or
the throttle cable or throttle shaft or something else is holding the throttle plate open; or
the Throttle Position Sensor voltage at closed throttle is out of spec (too high). This would tell the PCM that the throttle is above idle and it would keep the IAC in pre-position mode.
If the engine is up to operating temperature and it is hanging above curb idle when the truck is stopped, there are 3 likely causes:
the Idle Air Controller is sticking; or
the throttle cable or throttle shaft or something else is holding the throttle plate open; or
the Throttle Position Sensor voltage at closed throttle is out of spec (too high). This would tell the PCM that the throttle is above idle and it would keep the IAC in pre-position mode.
#8
I would do cheapest first - watch to be sure that the throttle closes all the way to the stop and there is at least a small amount of freeplay in the cable when it is closed.
Then I would monitor the voltage on the TPS gray/white wire. The ignition must be on and the sensor must be plugged in when you check it. A good TPS voltage with closed throttle would be about 0.50~1.25v. If it is much higher than 1.25v, that could cause the RPM to hang.
Then I would monitor the voltage on the TPS gray/white wire. The ignition must be on and the sensor must be plugged in when you check it. A good TPS voltage with closed throttle would be about 0.50~1.25v. If it is much higher than 1.25v, that could cause the RPM to hang.
#9
#10
#11
Originally Posted by rwenzing
I would do cheapest first - watch to be sure that the throttle closes all the way to the stop and there is at least a small amount of freeplay in the cable when it is closed.
Then I would monitor the voltage on the TPS gray/white wire. The ignition must be on and the sensor must be plugged in when you check it. A good TPS voltage with closed throttle would be about 0.50~1.25v. If it is much higher than 1.25v, that could cause the RPM to hang.
Then I would monitor the voltage on the TPS gray/white wire. The ignition must be on and the sensor must be plugged in when you check it. A good TPS voltage with closed throttle would be about 0.50~1.25v. If it is much higher than 1.25v, that could cause the RPM to hang.
how do i check the throttle closing all the way to the stop by myself and without driving truck? i mean if rpms rise when driving and clutch pushed in, how do i check it with it sitting at idle?
#12
Originally Posted by Jeremy102579
how do i check the throttle closing all the way to the stop by myself and without driving truck? i mean if rpms rise when driving and clutch pushed in, how do i check it with it sitting at idle?
BTW, the screw is a factory adjustment and you shouldn't change it.
#13
Originally Posted by rwenzing
Look to see if the throttle stop is contacting the screw after opening and closing it slowly. You're just looking for mechanical sticking or whatever. You don't need to be driving it at the time.
BTW, the screw is a factory adjustment and you shouldn't change it.
BTW, the screw is a factory adjustment and you shouldn't change it.
the truck was not running while i did this, should i check it while it is running?
how about the TPS, is there any way to check this sensor without hooking a voltmeter up to it, like the iac, you can test it by unplugging it, how about the TPS?
i noticed today that my idler pulley would slightly wiggle when pulling it back and fourth, could this cause a weird idle problem?
Last edited by Jeremy102579; 03-25-2007 at 08:18 AM.
#14
I would check it when idling just to be sure that engine vacuum doesn't change anything. You'll need to do the voltage test to check the TPS.
A small amount of side play in the throttle shaft probably won't hurt anything. More could cause a significant unmetered air leak. It's hard to predict how much would cause a problem with the idle.
A small amount of side play in the throttle shaft probably won't hurt anything. More could cause a significant unmetered air leak. It's hard to predict how much would cause a problem with the idle.
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