Hello All,

Couple of nagging issues with my 93 F250. Truck has the 351 and E40D.

I've had a persistent code 121 (KOEO) since I bought the truck a couple of years ago. TPS has been replaced twice with no change. Has anybody had this issue or have some additional troubleshooting advice?

Second are some IAC questions. Truck has always idled around 900-1000ish. I did change out the IAC in the past. Today I figured I'd pull the IAC connector, with the truck running, to see if it had any effect.....nothing...truck kept running with no change in idle rpm. Shut down and removed IAC connector. Measured 10 ohms across the IAC. Measured 11.2 volts across IAC connector with ignition on. Removed IAC and still looks brand new. The valve was open when I removed it. That normal?

Throttle body passages are clean as a whistle. Have sprayed carb cleaner all around the engine bay in the past, checking for vacuum leaks, but nothing found.

Put it all back together and here I am....wondering what the heck is going on.

Any advice you guys can pass on would be greatly appreciated.

Thanks,

Dan

 

Code 121 is "Closed throttle TPS voltage higher or lower than expected". So why have you been messing with the IAC when you have a TPS code? The TPS should measure less than 0.9v with the throttles closed, if it doesn't then either the sensor is bad or more likely since you also have a high idle problem.. the throttle set screw has been misadjusted by somebody and the throttle blades are open further than they should be.

 

Well...I messed with the IAC because I was there. I had the intake tubes off so I could look at the butterflies. Pulled the IAC connector and it did nothing.

Backed the throttle stop all the way out and nothing. Throttle body is clean as a whistle.

I never have been able to get a voltage reading from the TPS connector by backprobing, but I will try again in the morning

 

Didn't make any progress today in solving issue. Still unable to check voltages by back probing the TPS. Removed throttle body and took TPS sensor off. Checked resistance values with VOM and was smooth all the way through rotation. Measure 5 volts Vref at TPS connector. Took off the huge connector (whatever it's called) on driver side fenderwell and checked continuity of TPS wiring out to TPS connector. All checked good with no shorts/grounds and about .1 ohm resistance.

Slapped it all back together and still get code 121. Ran both KOEO and KOER tests and it's still the only code.

Any suggestions?

Thanks

 

Change the TPS sensor.

 

TPS sensor is maybe 2 months old.

 

Don't count on the TPS sensor being good just because it's new. It's usually rare but it's not unheard of for a brand new part to be bad.

Are you sure there's no breaks in the wires or loose connections?

 

I checked the wiring from the TPS connector over to the big main connector on the drivers fenderwell and all 3 had good continuity. It could be wiring from there to the computer...or computer?

 

Since you have eliminated the TPS and wiring I'd say you're looking at an EEC fault.

 

Hello,

Finally got to the bottom of my problem. After chasing all the wiring and trying out a new computer, I took off the BBK throttle body (didn't mention I had one installed because I never thought it was related to the issue) and threw the stock TB back on. Code disappeared.

Finally figured out the TPS end of throttle shaft on the BBK throttle body was not quite long enough. Normally when you install the TPS you place it over the throttle shaft and have to slightly rotate it to line up the two mounting screw holes. This slight rotation sets the TPS resistance into a range the computer is expecting....hopefully. Figured out the TPS was not being rotated enough when screwing it down to the throttle body. Either the screw holes in the body were off or something was wrong with the throttle shaft.

After playing 200 questions with BBK (tech support guys put you through the ringer before they'll even admit something can be wrong with their parts) they agreed to look at it. Throttle shaft was a little too short and they replaced it. Installed reworked throttle body on truck and all is back to normal.