I'm getting a code 31 from my key on, engine off scan in my 90 302 F150. That is for EGR vacuum regulator, EGR position sensor, and pressure feedback for EGR sensor. (It also comes out in the key on, engine running).

I replaced my EGR position sensor last week. The EGR valve was stuck (probably for some time) and I freed it up with some deep creep. My idle is up around 1300-1500, but I don't know if that has anything to do with this.

What should I look to do?

 

I am reading up on the forum seach for "code 31." Looks like Im in for a ride.......

 

I just recently replaced the TPS and EGR position sensor and cleaned the EGR and IAC. The EGR exhaust line had a lot of carbon build up in it. It seems like the more I fix, the more problems show up.

I took the vacuum hose off the EGR and applied 20 in Hg of vacuum with the engine running. The idle speed came down to normal (from 1500rpm), but stumbled a lot. Relieving the vacuum made it go back to where it was before. There is a tiny bit of vacuum coming from the green hose that was connected there.

I followed that green hose around the back of the engine and to the right side where the TAD/TAB solenoids are, and it hooks into a device with a round top, another black vacuum hose, and an electrical connnector with a black wire and a red wire coming out of it. I assume this is the EGR vacuum regulator? I thoguht it was the thermacter air bypass solenoid......because I also replaced it just a week or so ago because the round top had melted through.....don't know how that happened, I just got this truck about 2 months ago. I unplugged the green vacuum hose there. Almost no vacuum coming from the unit. I unplugged the black vacuum going to it and it had plenty of vacuum. I hooked it up directly to the EGR valve and it behaved as when I had 20 in Hg by vacuum pump on it.

I ran a KOER on it while I had this vacuum applied to the EGR. Still got a 31, but also a 22 and an 18. I don't have a tachometer to check the MAP sensor. I'd like to find the EGR back pressure unit as suggested in some of the other code 31 links....I don't know what to do next.

 

Was the TPS replaced before the 1500RPM idle problem?

The 31 sounds like its a bad harness. To test it try this:
-Take EVP off the EGR valve, but leave it plugged in.
-Push the EVP pintle all the way down
-Run a KOEO test
-You should get a code 34, or 35.

Put the vacuum gauge at the intake and measure how much inHG of vacuum you have at idle.

 

idle is high before and after TPS replacement. I replaced it because I wasn't getting a resistance change when I opened the throttle. I was hoping it was the high idle source, but apparently not. I was having some difficulty measuring the voltage to the TPS. I don't think I ever got one.....

 

Are you clearing the codes after every repair? If not then the codes will stay and then you will just see it over and over again. I have fixed a lot of EGR problems by cleaning out the carbon and checking that all the lines are clear.

 

yeah, after every fix I unhook the battery for about a half hour.

I just let did that and did a KOEO test with the EGR position sensor unbolted from the EGR. I held the pin all the way in through the test and it still gave me a 31..... That same harness is near the tps, which also doesn't seem to be working properly.....

 

oh yeah, and my gas mileage sucks too....

 

Ok..I confirmed proper operation of the TPS, and the harness by checking voltages and resistances.

I also did the same with the EGR position harness. My new EGR position valve is measuring 4.41 kohm open and .45kohm closed. From other posts on here i've seen this is a danger with aftermarket EVP's. I went back to the store and probed one on thier shelf...same thing (borg warner brand). If my computer is expecting 5kohm-.1kohm and is getting 4.41-.45...I can see why I'd still be getting codes. I'm on my way to Ford to get the OEM one. I don't think it will solve all the problems though....

 

ONLY USE OEM MOTORCRAFT EGR POSITION SENSORS. I took the borg-warner out, put in the one from the dealer and no more code, no more light. I'm getting a code 21, engine coolant temp sensor out of range, which would explain my high idle...the computer continually is trying to warm up to operating temp. I'll replace it when the truck cools off.

 

Kewl! Nice find Puck!
Tim

PS
Jim - nice sig "tweeks-creaks-leaks & squeaks!"

 

I replaced my ECT. No more code 21, but no change otherwise. Still idle high. Now I only get a code 13 with no leads.

I don't think it is a vacuum leak, because I measure 22 in Hg off the manifold at the MAP sensor. (which I replaced because I'm getting desparate). The idle returns down more normal if I pull the vacuum off the MAP. I get lots of codes running a KOER that way though, MAP related.

My high idle started when I took off my two big air intake hoses to the throttle body and deep creeped it all out good. After suggestion something came loose and is blocking the butterflies, I did it again. No change. I made sure the hoses got back on tight. Only thing I can figure now is that the deep creep treatment I gave the intake cleaned out some gunk that was plugging a hole in the intake somewhere and now un-metered air is coming in.

I'll do some thread searches for code 13, but I'm about out of weapons and will have to surrender to a shop............

 

well 13 is cannot control low rpm.
Did you plug the IAC back in? Sounds like you need to be in this area or out-n-out replace it.

edit - after reading th posts from the top, its odd that the idle returns to normal with the egr wide open (20in vacuum). Is there a junkyard nearby that you could scavenge a different egr valve?

 

yeah, I'll try to find another EGR...similar thing happens when I unplug the vacuum from the map, or apply20 inHG to the EGR....idle goes down to where it should be, but doesn't run well.

I did the forum search for "code 13". I'm going to try the following things:

unplug the IAC - the idle should drop, right?
check the throttle cable and throttle stop
do the haynes check for the air intake sensor
look around the EGR and IAC gaskets to the intake for leaks
look at/ maybe adjust/ timing (although I thought I should have idle under control for that....)

Suggestions while it do this.??........

 

Unplugging the IAC should almost if not kill the engine I think.
Good point about checking the thottle cables. check the cruise control cable if you have one. make sure the idle adjust screw isn't blocked, bent, or slipped.
It just seems like its got to be something really simple doesnt it?