Plow season went well, but rather suddenly with warmer temps the truck is running awful at idle.

Here's what I've noticed, and done so far:
-hard to start
-obvious vacuum leak after shut down
-replaced brake booster (original).

No more vacuum leak.

Unfortunately still runs terrible at idle, feels like it is missing. RPMs seem low (500) and kicks a bit. A bit of pedal and it smooths out.

I replaced the air filter (and removed the mouse nest), plus new cap and rotor (old one, and plugs / wires are 4 years old). Plus and wires are the same (for now). A few years, but less than 6k miles on them so far.

I pulled the codes (but didn't warm it up for the 2nd part of the test. Maybe tomorrow). I'm not sure if some of these were being thrown from before the brake booster replacement.
KEO
334 EGR Valve closed voltage high
172 HO2S sensor fault- Lean
556 Fuel pump relay primary circuit failure
628 Excessive converter clutch slippage

KER
334 EGR Valve closed voltage high
172 HO2S sensor fault- Lean
412 Cannot control RPM during high
116 Coolant temp below expected (truck not warmed up… not a surprise)
126 MAP or BARO above or below normal
536 Brake on / off not actived during KOER
632 Overdrive cancel switch no action during test


Any hints what to try next?

I was thinking Idle Air Control valve, but now I'm thinking maybe EGR.

Other work past winter includes new heads (no more exhaust leak!), rest of the engine was clean and check out well.

Other hint being the ABS light is one (came on after the head work... makes no sense. Sensors and connections clean. Went off for a while, then returned).


Any hints / thoughts greatly appreciated! I don't mind tinkering for a bit, especially as none of the independent shops around here like to work on one tons. The best place seems to be the dealer... and that always gets expensive quick.

 

Code 334 (KOEO/KOER): EVP circuit above the closed limit of 0.67 volts.

This indicates the closed EGR feedback signal is too high. This can be caused by a stuck open EGR valve, bad EGR valve or faulty EVP sensor. Verify the EGR valve opens and closes with vacuum applied and removed. Verify the output signal with a meter. Sometimes some carbon build-up can prevent the EGR from fully closing.


Code 172 (CM/KOER): HEGO sensor circuit indicates system lean

Could be a symptom of a partially stuck open EGR valve/Code 334.


Code 556 (KOEO/KOER): Fuel Pump circuit failure

Indicates a problem sensing the Fuel Pump Relay status. Has the relay been bypassed?


Code 628 (CM): Converter clutch Lock-Up error (E4OD)

Clear the code, then drive the truck again. Recheck for stored codes. Verify the transmission fluid is clean and at the proper level.


Code 412 (KOER): Cannot control rpm during KOER high RPM check

Probably related to the vacuum leak caused by the EGR valve. If the EGR checks out then look for vacuum leaks.



Code 116: ECT out of self test range 0.3 to 3.7 volts.

Operator error, did not fully warm up the engine before running the KOER tests.


Code 126 (KOEO/CM/KOER): MAP sensor out of self test range 1.4 to 1.6 volts

This could be caused by a faulty MAP sensor. Use a meter that can measure frequency to verify the signal. Could be a contributor to Code 412 and poor running.



Code 536/623: Operator error during KOER tests, did not cycle Brake On/Off or Transmission O/D switch at the proper time.

 

Thanks

I just got in from testing again (after warm up), and of course half the codes (those relating to not warming up properly) are gone....

Now to tackle the EGR valve.

Thank you!

OH - and during the KOER test the idle was higher and it was running much more smoothly... makes me wonder if it is a sensor rather than the valve itself

 

my 90 did the same thing but would stall out when I came to a stop, idle air valve was bad and not letting it idle, changed it and was back to normal idle and took care of the rest of the codes it had

 

Please help me! What are the symptoms when the Idol Air Valve and the EGR Valve are bad?? And where are they on a 91 F350 gas engine? Thanks

 

If you have a 460, the IAC is right under throttle body. Follow air tubes from air filter and there's a smaller one that branches off to underneath throttle body area connected to IAC. The EGR is on the driver side rear of engine on top. There's a tube that connects exhaust to it and its bolted to side of throttle body.


Faulty IAC can cause either stalling or higher ilde if its stuck or not working

 

Thank you! Yes its a 460. I'll tell you what happened and I pray you or someone can help me a little more. The key got left on, ran my battery down so I jumped it to start it. Drove it 40 miles & it ran great, normal. Got in it the next morn to go home & it was dead. Put the charger on all day, it started drove home, ran great. The next day dead again. Get a new battery, now it won't turn over, dead.. So I buy a solenoid and install it. Pickup starts but won't idle, will die when I stop and runs rough now.