I have had a recurring problem ever since I put the cam in the 4.8, and it's carried over to the LS1 even though I changed throttlebodies AND TPS sensors.

I keep getting a TPS (I think is P0121), mainly at idle. Sometimes, it will go away. Other times, it will stay on forever. I've also gotten a MAP sensor code off and on as well.

Now, I haven't replaced the TPS with a BRAND NEW one--a buddy had an extra TB laying around so I snatched the sensor off of that. Should I try a brand new GM sensor first, or is there something else that could be causing the problem? Any ideas at all? Can this be tuned out w/ EDIT?

It doesn't seem to affect the performance of the truck, but damn it's getting on my nerves.

 

Anyone?

 

That code is actually looking at the relationship between the MAP sensor and the TPS. When the PCM sees a TPS angle that doesn't match an expected MAP range, the code sets.
I think the problem is not with the TPS, but with the MAP sensor. I would look at the wiring to the MAP sensor or maybe try another one. I think you ruled out the TPS when you tried another throttle body.

The problem has to exist for 15 seconds for the code to set, so if you could get a scan tool on there you might see where the problem is.

You can turn it off with Edit but I wouldn't advise it; I think you would be covering up a problem that way.

 

Okay, I'll try that. Thanks John!

BTW--I didn't get any instructions w/ my 4L80E conversion harness. I saw that the wires are marked, but that doesn't mean much to me. Can you (or anyone) hook a brother up?

 

Yeah, there aren't any instructions with it. Since the 4L80E adds the ISS (input speed sensor) you have to route those 2 wires up to the PCM.
Unhook the connectors from the PCM, pop the gray cover off of the back so that you can see the position numbers, pop the RED cover off by pushing in on the latches on each end, and insert the 2 terminated wires into the proper position (21 & 22). Reverse the procedure and you're ready to go.

The other part is just a direct plug in between the old 4L60E harness and the 4L80E transmission.

 

thanks John! Are the slots on the PCM marked, or do I need a diagram?

 

Once you pop the long gray cover off of the back, you can see all of the numbers above each terminal hole.