Did you remove the SPOUT plug when checking the base timing? If not, the timing is now severely retarded.

 

The computer is expecting a Base timing of 10 deg, this is where you need to set it with the Spout connector removed.


You have a known TPS Failure Code, the next thing to accomplish is the resolution of this fault.

 

The timing was checked when the engine was at operating temperature and with the spout removed. I agree, my next task should be to hunt down that TPS failure code. As I mentioned before, the TPS sensor was replaced a few months ago. I will still check it, is there another potential cause for this issue? maybe faulty wiring?

 

first you have to do what they are asking, to the TEEEE! tell them what the volts is when 'you test it' is not an answer they can help you with, so
1. do you have a DVM(digital volt/ohm meter) do you know how to use it, if you dont know how they will help you figure out a different way to check it
2. was timing checked with spout out? what was reading if its not on 10* get it there, not from 20* down to 15* they asked for a specific timing adjustment, and tell them what happened
3. put spout back in and read timimg with spout in is timing jumping around(good its supposed to computer controlling it) if it dont move around what is its constant reading
4.how to check tsp Use a volt meter, and probe the TPS wire (the center one) and probe the negative to the black wire (signal return). Leave the harness plugged in, and turn the key on, but do not start the engine. With the throttle closed, it should be less than .9V and wide open throttle should be ~4.8V but not 5V, This will show you what the computer sees from the sensor. In between closed and full throttle, the voltage should gradually progress upward, and not jump around. If you don't have the correct voltage there, check the orange wire for a constant 5V (key on). If you do check resistance, (tps unplugged) you only need to probe between the tps signal wire and the signal return (black wire). Resistance at closed throttle should be 3-4K Ohms, and 350 Ohms at wide open.
5. for 4 days they have asked you to do these things and you still haven't but you still want help, why should they help if your not even trying to do as they ask, they cant come hold your hand, nor would they if your not even attempting to help, take to a shop see what they charge you for working on it for 4 days, I dont know how much $$$$ but you can bet your last dollar, it wont be free

 

If the base timing was at 20 as you stated it would be a bear to start when the engine is hot and it would ping excessively IMHO. I suspect the outer ring has slipped on the balancer so now it's anyone's guess where the timing is set. Or you used the wrong timing pointer.


Highly suggest you check the output with a DVM as described above. Since you have that fancy BBK throttlebody there is an adjustment procedure to set the base idle. I suspect the throttle stop screw may be set too low since you most likely have a vacuum leak (which causes a high idle). This will cause the TPS output to be outside the normal range. Perhaps the screw is purposely set too high? Verifying with a meter will tell you the story.


A lot of things going on right now. Start troubleshooting the TPS error code, then tackle the timing. Get those resolved then you can move onto the backfiring and rolling idle.

 

Anything is possible on these old trucks.
Since the Computer controls the fault codes, a faulty computer could be putting out bad info about a sensor, but a new sensor can be faulty as well or mis-adjusted.
And yes, wiring in these old truck can have issues.
You just have to work through the process of elimination as time permits.