Throttle Issue???

[JBihl]

Hi, I've been battling this issue for about the last week.. I've read through the forums pretty good and tried my best to diagnose the issue with information found here but have had no luck.

95 GMC Sierra 2500 6.5 TD 160k. I drive this truck daily to run service calls.

At first I was driving down the interstate at about 65 mph and it seemed like it lost power for a brief moment but then drove the rest of the day just fine. The next day the throttle began to act erratic, like either no throttle or wide open throttle, but it would idle fine. I was in the middle of my work day and about 2 hours from home so I just continued driving and it made it home just fine, was an interesting ride. The next morning I fired up the engine and the idle has now became erratic (jumps to and from 800-1500 on its own)I put in my spare PMD and it made no change. I checked for codes and came up with two relating to the APPS. (no STS light) Seemed simple enough so i ordered a new APPS, I was able to track down just the sensor for $60 opposed to the whole assembly! Almost soiled my pants when the parts shops all wanted $400-$500 and couldnt come up with just the sensor.. it just came in today.

Well, I installed the APPS just 30 minutes ago and now I have the STS light on and absolutely no throttle, but its idling nice and smooth..

Also, I briefly checked the grounds and they appeared fine but tomorrow morning I think that I'm going to remove and clean them and maybe replace the connectors if they seem bad... Any other ideas would be greatly appreciated..

 

[NVW]

First thing is to clean the grounds, esp. the 2-3 on the trans dipstick.

 

[Burning oil]

New APPS bad? does old one give any throttle?
Got another PMD to try?

 

[JBihl]

Both APPS now produce the same results and I've ran the spare PMD a fewdays about 6 months ago.

 

[Burning oil]

Maybe IP is wore out? Can't think of anything that would cause jumps in RPM except PMD and IP.
Done any recent work to it?

 

[FellowTraveler]

Perhaps, up under the passenger foot well you will notice the harness comes through the firewall and hangs down and swings up to the ECM and it be pushed by a passenger stretching out on a long drive etc the harness pins can be pulled out at the ECM and have intermittent contact this happened to me a few times until I strapped the harness in place.

 

[JayTheCPA]

WELCOME TO TTS!!!


Am leaning toward the IP (sorry).

First, make sure the grounds are good.

Second, do the 2K RPM test when the motor is warm (idle, slow increase to 2K, hold for a couple seconds, slow decrease to idle, repeat 10 times); if the RPM's do not match the throttle position, want to run-way, or results are inconsistent from each cycle, the IP is probably questionable. If the IP was never replaced, at 160K it had a good run. If the IP is the source, consider going with a new unit as it should come with parts that tolerate ULSD. Going with a reman'd IP will save money, but I developed an allergy to reman'd IP's.

If you do need to replace the IP, consider having the injectors tested and balanced while the system is apart. If there is no known history on the injectors (or are original), consider replacing them as their service life is 100K; anything past that is a *big* gamble on keeping the pistons and cylinders healthy.

And while working on the fuel system, if the lift pump has no known history (or is original), consider replacing that as well. While there, add a fuel pressure gauge to monitor the LP's health. The motor will run with a LP failure, but this will eat into the IP's service life and cause issues with going lean when you need full throttle.