every once in a while...

[grapegoat]

I have a 96' ranger 2.3L 5speed 2wd 155K.

Truck starts fine, runs fine, idles fine all day sitting in my driveway.

However every once in a while, when im driving through town and approach a stop, I press the clutch and pull it into neutral and the engine doesn't want to idle down.

Once I come to a near complete stop, sometimes it will idle down, but sometimes it wont. Sometimes it will stay high for just a second or two after I stop and then idle down. Sometimes it will just stay high.

this rig was not blessed with a tach so Im not sure what rpm exactly. my guess is around 1500-1800 rpm. it will just sit there.

If I am rolling down the road and pull it into neutral, it will never idle down. Not until I come to almost a complete stop, (less than 5mph).


while Im stopped, and the truck wont idle down, If I put it back in gear and drag the clutch with my foot on the brake, it will bog the engine and then it will idle.

so what do you guys think? vacuum leak? sensor? its weird how it doesn't do it every time. Maybe a few times a day. so I don't know where to start.

 

[RonD]

For emission reasons the idle will stay high(1,100+) until speedometer gets below 5MPH.
This can also change with clutch position, i.e. pedal in or out, it will hold RPMs at what they were when pedal was pushed in, this lowers emissions and aids shifting.
Computer doesn't know what gear you are in, it just has a clutch pedal switch and a VSS(vehicle speed sensor).

 

[tomw]

I think I would take a look at the IAC. The Idle Air Control is in charge of keeping the engine idle steady when loads such as the power steering pump or the A/C compressor are added and removed. If it sticks, the idle may be too high or too low.
You can tell if it is working by starting a cold engine and then noting how the rpms drop from the fast idle to normal over time as the coolant warms up. If you get no fast idle cold, the IAC is not responding or not getting the command.
The older models would turn off the injectors, or cut them way back, when in 'coast down' as you approach a stop sign to help control emissions. Seems to me that 1100 rpm as a 'coast down' is too high, as that would be way over 15mph in my truck. I think it is turning about 2k when going down the road at 45mph. Anyway, it couldn't hurt to check the IAC. And maybe the CTS - coolant temp sensor.
tom

 

[ranger1997]

IAC My first choice. I've had that problem, get a motorcraft


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