I have a 94 b4000 that I need some help with. I have codes 121 TPS is/was out of range 335 EGR feedback signal is/was out of range. the egr solenoid is opening intermittently at idle due too tps not reading correctly. The first tps I put on read 1.5v closed and 5v open. I just bought another one and it reads 0.09v closed. Both sensors read around 0.03v off the throttle body. Any idea what might be causing this? I have the air adjust screw all the way. I have put a new egr solenoid on. I checked the three wires going to the dpfe sensor and they read 0.21v 5v and 0v. Im not sure which wires are which.

 

TPS code is unrelated to EGR issue/code

Unplug the 2 wire connector on EGR Solenoid, so it can't open
Start engine
Make sure the EGR Valve is now not opening at idle
You are testing to see if "new" EGR solenoid is, or is not leaking

Shut off engine
Plug back in EGR Solenoid
Start engine
See if EGR valve is now opening at idle
If so then Computer is controlling EGR valve, and doing it incorrectly
OR
The ground wire from the EGR solenoid to the computer has a "bare" spot, and is grounding out causing the EGR Solenoid to open now and then
EGR Solenoid has a red 12v wire, it should have 12v full time with key on
The other wire is the ground wire that runs back to computer
Computer will "pulse" the ground to open EGR solenoid a little or alot to control the amount of vacuum going to the EGR Valve
At idle that wire would not be grounded at all
You can test that with OHM meter


The DPFE sensor could be your issue, if above is NOT
335 (O) EGR feedback signal is/was out of range – EVR or PFE

Computer TESTS if EGR system is working on start up, which means it opens and closes the EGR valve a few times to make sure DPFE sensor shows the change in pressure
This IS the "EGR Feedback signal"
And computer will open EGR Valve more and more to do this test to see if there is any change in pressure signal from DPFE, so this could be why you are seeing EGR valve movement at idle

Never had much luck testing DPFE sensors, even with a vacuum pump, so.......................I usually just replace them since they are a common failure after 4 to 8 years old


TPS
Your first test was almost correct
0.9v throttle closed
4.5v throttle wide open
Thats spec

Check if someone turned the anti-diesel screw in, looks like and idle screw, it's NOT that
Put original TPS back on
Test Center wire with key on engine off
Should be 0.9v
If 1.5v turn anti-diesel screw out, counter clockwise, and watch voltage, when it gets down to 1v or so, manually open throttle and let it SNAP closed
See what voltage is now,1v is OK , but see if you can get 0.9v
Now open throttle all the way and see if you get 4.5v, slightly higher is fine

TPS and anti-diesel screw are now set

If your engine stalls at idle then your issue is IAC Valve not anti-diesel screw