302 being stubborn
Cargo Master
Joined: Mar 2007
Posts: 2,935
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From: Arcadia, Fla
The speed input(VSS) is used for the "dashpot" control of the engine's idle when coming off the throttle from cruising.
Pulling codes without moving the truck usually sets that code for no vss if the ECU never seen any speed input.
Cargo Master
Joined: Mar 2007
Posts: 2,935
Likes: 34
From: Arcadia, Fla
Check the MAP sensor vacuum line before the TPS. I had a bad MAP vacuum line that would cause the timing to jump around at idle. The ECU got a bad vacuum reading at idle and though the engine was higher in RPM. I never got codes too on that issue...
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
Could you explain in more details your hypothesis?
Code 29 is a KOEO only code so perhaps if the truck has not moved in the last 80ish key on sequences it could be triggered but IMHO that is a stretch.
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
Put the new TPS on and it made a big difference, very greasy and black in the intake though. It started up beautifully revved it up, sounded great, let off throttle and it died. It was pretty hard to start the second time, cranked a little while and had to hold it wide open for it to catch. It was also hard to get it to idle, had to very gently ease off the throttle. The timing is still right about 5-10* when revving and idling.
Have you actually measured the TPS signal with a meter from closed throttle to wide open?
Cargo Master
Joined: Mar 2007
Posts: 2,935
Likes: 34
From: Arcadia, Fla
Once on my 89 while checking a EGR issue. In both times, I cleared codes and hard reset the ECU but never move the vehicles.
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Laughing Gas
Joined: Dec 2013
Posts: 884
Likes: 7
I haven't checked the voltage, the batts on the multimeter are dead, also not sure exactly how to check the tps output voltage. I'll probably pull the IAC today and clean it up, and check the vac line because I'm sure it's cracked somewhere.
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
Good info here:
TPS
Pierce the wires with small pins, attach your meter leads, turn the key to the ON position. Measure the TPS at closed throttle, record the value. Slowly open the throttle, watch the signal output for signs of dips or peaks as you go to wide open throttle. It may take a few tries with a DVM to get the feel for how the meter reacts. I highly suggest turning off Auto-Range on the meter.
TPS
Pierce the wires with small pins, attach your meter leads, turn the key to the ON position. Measure the TPS at closed throttle, record the value. Slowly open the throttle, watch the signal output for signs of dips or peaks as you go to wide open throttle. It may take a few tries with a DVM to get the feel for how the meter reacts. I highly suggest turning off Auto-Range on the meter.
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