Check ALL of your connectors ( and there a bunch of them ) I had a similar problem as yours, replaced the APPS, both batteries and high and low AC cutout switches still no joy!
After cleaning and checking every ground I could find all to no avail I finally cried uncle and took it in to the dealership. We are really fortunate to have a good dealership and GREAT diesel tech locally. He ran the diagnostics on it and found a bent pin in the C-125 connector on the firewall above the valve cover. I have no idea how it got bent but it was causing a voltage spike to my APPS every time the AC clutch kicked in.
In short, check all of your connections for moisture ( I used a can of compressed air for computer cleaning and then re greased with di electric grease ) and check the pins in them.

 

I checked the connector on the TPS & cleaned it. Still no improvement. When just trying to drive 55 or 60, this thing is up & down. If I hammer it, it seems to runn OK. Do I have a TPS problem or an electrical problem? Will sticking a 12 volt ignition hot wire straight to the TPS do anything for me. Enquiring minds want to know. Please help.

 

As was mentioned before, there are two connectors above the valve cover on the firewall. Check these out real good, I had some trouble with them after the last engine change. They have the connect to the PCM from the ECM and can screw everything up.

 

BIGHEAD,

It sounds like you have some sort of electrical short. It may be that when you floor it that the engine torque's up and somehow alleviates the shorted connection. I have had this happen on vehicles in the past.
Like Haulin and Clunk have said, check those connections above the valve cover thoroughly, as well as any other connection that is PCM related that you can find.

Good Luck!

 

Thanks guys.

 

The truck is running worse & worse. If it is electrical, should it be getting worse & worse. If it is the sensor going out, I could see it getting gradually worse, What do y'all think?

 

Ok fellows, I found out how to fix your APPS/TPS problems. Just go buy a new TPS sensor & let it lay in the passenger seat. I picked up a new one Friday. I was on the way to get it, & my check engine light went out, & the truck went back to running fine. What gives? It must be trying to fake me out or something.

 

You may have what I have in mine since new. I have scope readings if you need. I don't know where the interference is comming from but replacing the ALt and battery and ECM doesn't help at all. All were good according to the oscilloscope. By chance do you have access to a scope???????? I know not likely. I could chase a load into the PDC but why I don't know.

 

News Flash. Truck got to running so bad that I swapped in the new TPS today. All seems to be well now. I noticed the throttle cable unwinding & fraying. I snipped off as much as possible. Anyone know how much trouble it is to change this out with a new cable?

 

Just curious--how is the APPS for the auto be any different from manual? I bought a used one on ebay and have no idea if it is from an auto or manual but it seems to work...

 

mine though the o122 code (apps) change it out with my dads to see if it was bad , and no diff. took it to a friends that had a snapon reader and it showed it was getting voltage from the idle part of the apps but not the go peddle side. It would show voltage with the engine off but when you started it it would loose it . did a test on the wires and they were good. talked to Bob about the ecm he said to change it out with dads even tho his is a so and mine is a ho . It ran like crap but it would take throdle tho so I order a ecm though my local salvge yard for $200 hope this fixes it

 

When I first bought my 99, I was having similar problems. Whenever I got to a particular spot in the range of the accelerator pedal, my truck would go straight to idle, and the check engine light would come on. It did this to me a bunch of times, and after a day or so, the check engine light would go off, and the whole thing would happen again. It finally got to the point where it was happening 2-3 times a day. So I had the codes checked on it and got the APPS code. The idiot tech then tried to tell me that he never saw one of these go bad, and said it was probably my lift pump or injection pump. What an idiot! So I yelled at him and drove away. To make a long story short, I replaced the sensor and have had no problems with it since (12K). But this is the way that thing works; there is a sensor that rides the spring that your throttle linkage connects to. If your truck has seen alot of mileage at a single speed, like the same cruise control over a few years, then the sensor can wear that exact spot out on the spring. So when you accelerate or decelerate and hit that spot, then your ECM tells your motor you're getting no fuel. Might be what you are experiencing. BTW, I have the 6 speed and got a used APPS out of an automatic from a friend, and it is working just fine! Good luck

 

BigHead, My truck is doing the same thing. Around 45-50mph, in OD, with light pedal the truck will shudder like crazy. If I accelerate a little threw this area the shudder stops. If I run without the OD it will not shudder. I was showing low voltage TPS/Apps. I've reset the voltage. That did not help. Also checked all the ground connections, Batteries are good. This is driving me mad. If I find out what is causing this I will PM you. Give us an update if the new TPS does the trick.
How much did you have to pay for the TPS and where?

Regards,
Gene

 

Are your symptoms, Traveling down the road the truck goes to an idle, then it seems that it come back to life. You might want to put some stuff down for your signature, so that we would know more about your truck. Mines manual, is yours manual too.