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Going into High idle

P

Possum

New Member
Messages
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Location
Greenville, SC
I have a 96 6.5 and it keeps going into high idle all of a sudden. Sitting at a stop sign and it will lunge forward when it does it. Between 40 and 50 mph it keeps down shifting then upshifting continously. Replaced PMD. Got a #9 resister in it. Will 180 degree thermostats cause it to do that? That is really the only thing I have changed. I thought I would try the 180's for summer towing.
 
Might have two issues.

Yes, if the crossover's sending unit (coolant temperature) is failing, the computer will command shifts to try and warm the motor.


But first, I'd eliminate the injection pump by trying the Idle-to-2K RPM test:
- Engine warm, all accessories Off.
- Slowly and steadily press on the throttle to increase RPM's to 2K, hold for a second, and slowly and steadily release back to idle.
- Repeat above step 10 times (No, not kidding).

A passing condition is when the RPM's match the throttle input each time.

A failing condition is when the RPM's do not match the throttle input each time where possible events are:
- RPM run-away.
- flat-spots (RPM's do not change for a period of time and then 'jump' up / down).
- RPM's not changing at the same rate as the previous cycle.
- each cycle presents something of a different response than the previous cycle.


If the truck fails, chances are good the IP needs replacement.
 
Yeah I learned it the hard way that temp sensor controls a lot of stuff.. in fact I think that was what originally brought me to this forum and how I became a member LOL.
 
Thank-you. Sounds like what my '95 has been doing. Change the pmd yesterday with a #9 resistor. She won't even idle down when started cold. Right up to 4-5,000 rpm's and blacker than black exhaust. Guessing the ip is next.
Any ideas on throttle position sensor?
I have a mechanically inclined neighbor with a code reader we're gonna slap on the Beast...
 
GMMomma74 said:
Thank-you. Sounds like what my '95 has been doing. Change the pmd yesterday with a #9 resistor. She won't even idle down when started cold. Right up to 4-5,000 rpm's and blacker than black exhaust. Guessing the ip is next.
Any ideas on throttle position sensor?
I have a mechanically inclined neighbor with a code reader we're gonna slap on the Beast...
Click to expand...
The TPS can be tested with an ohms meter, need to hook to the ground and the sensor terminals with the meter then slowly run the pedal through its paces and watch the meter to fail to decline in some places or the meter drops out in some areas, takes a few tries to get the pedal movement and the meter synchronized to the eyes but that's about all I know how to doooit. LOL
 
Is his OBD1 or OBD2 I always get confused about the cutoff year.. did you get the temp control sensors in?
 
Stoney said:
Is his OBD1 or OBD2 I always get confused about the cutoff year.. did you get the temp control sensors in?
Click to expand...
My 96 is OBD2. I have the new sensor but haven't put it in yet. By time I get home from work it's 97 degrees outside.
I'll try and put it in tonight.
 
@Possum i just realized that you live in Greenville SC. I live in the Greenwood area and I work in Greenville. There are two more members on this forum that live around our area
 
Check the cts plug closely. It's not uncommon for some coolant to get on the pins, corrode them, and get a poor connection. I've seen this happen several times. Had to remove the pins, use a pipe cleaner and some electrical spray cleaner, clean the pins up, re-assemble, put dielectric grease in the plug, and put it back together to fix this kind of problem long term. Coolant temp sensors are pretty reliable, but the connection is another story. Replacing the cts will correct it until the pins get corroded again, so I always at the minimum spray the plug out with cleaner just to be safe.
 
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