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.

?????

 

You coast in neutral to stops??

When you clutch in and the rpm's rise, it sounds like an engine idle problem. There's a sensor not doing it's job somewhere.

 

not coasting in neutral to stops....when coming to a stop in say 4th or 5th gear, and getting down to 20mph, i push the clutch in and shift to neutral and brake at same time, then the rpms go up while i am stopped , then when i start back up in 1st, they go down until i accelerate.

 

which sensors could be causing this?

 

noticed the idle comes down to about 700-800 at most braking to stops, but as soon as i push in the clutch, it jumps back up to like 1200-1400.

any ideas?

 

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.

 

which should i start with?

iac valve?

 

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.

 

My truck has the similar problem of having the rpms rise between shifts..they rise about 200-500rpms and then slowly drop off. The truck does need an oxygen sensor but im wondering if this is actually the problem..any other ideas?

 

o2 sensor would not be a problem.

ok guys, with the engine running, i unplugged the iac valve and the truck almost stalled, according the my Haynes, this should happen so i am guessing the iac is fine.

 

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?

 

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.

 

i am no mechanic by any means, i took off the plastic cover and noticed the idle throttle or whatever you call it, it moves open and closed very easily.

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?

 

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.