New to the forum. Idle issues with this truck. It keeps giving me EGR fault codes, but the 88 B2 2.9 did NOT have an EGR valve. I have looked and looked in books and online here and can not find anything about an EGR on this engine nor can I find it on the truck. Engine is original with low miles. I am at a loss here after days and days of researching this. I am replaced a number of parts so far, and getting no changes. So far I have changed the MAP sensor, Air Intake Sensor, Air Speed Sensor, and PVC Valve.

SYMPTOMS:
-Cold start idles up to 2k RPM, then then drops down and surges up and down
-When surging, it gets real low and will cut out after about a minute
-have to keep reving it to keep it runing
-when I put the truck in gear, it will idle back up high and stay running
-engine light will blink for a few minutes
-when in gear running, engine is fine. When stopped, engine idles fine
-after it warms up, it will idle fine.

Here are the codes I am getting from my scanner, and what the book that comes with the scanner calls them out to be:
(KOEO CODES)
31 - EVP or PFE circuit below min voltage
31 - EGR valve control sensor fault
31 - EVAP control system below min voltage
84 - EGR Vac regulator circuit failure
84 - EGR Vent fault
89 - AXOD Lock up solenoid (LUS) circuit failure

KOER CODES:
31 - EVP or PFE circuit below min voltage
31 - EGR valve control sensor fault
31 - EVAP control system below min voltage
25 - No knock sensed during DRT
74 - Brake on/off (BOO) switch fault - closed circuit (funny my brake lights work fine)

 

Welcome to FTE.

No replies yet, so will see if I can get things started. Good idea to have scanned for & posted All trouble code clues.
SO, lets think about this some more.
EGR isn't used at idle after a start, so isn't likely to be guilty of idle woes, BUT the EVAP system is used at cold start-up & you have trouble codes for that system, so concentrate your idle quality trouble shooting efforts on that system & remember we are to work & put right the Lowest code number first. Since you have a low control ref voltage code, I'd begin with that & since the engine computer is the source for the 5 volt reference, back probe the ECM electrical connector to see if its there, as it controls All systems. If not, or its low, suspect the ECM. If ok there, suspect a wiring run, or electrical connector problem. Seeing as how you say its low mileage, suggests its sat somewhere for a while & mice like to chew on the wiring insulation so keep that in mind.
Also since this is a Vintage ride, dry-rotted vacuum lines & rubber fittings & maybe a mucked up IAC, belong on the suspect list too!!! A bunch of beginning thoughts for consideration, let us know what you find.

 

Ignore the KOER test since you need to diagnose and repair KOEO faults first. I’m leaning toward operator error for the KOER codes 25 & 84. I’d also be inclined to look at the IAC not being able to control the idle. If you unplug the IAC when the engine cold and then start the truck what happens? As mentioned are the vacuum lines and hoses in good condition?