Code 31 (EVP) = Roller Coaster Idle?

[Darkwriter77]

EVP being the EGR Valve Position Sensor ... not EVP as in "Electronic Voice Phenomenon," of course.

The only code I'm still getting that I haven't slain yet is Code 31 - EVP voltage below minimum. The EGR Position sensor I've got on there now is new as of three months ago, and I've had this roller-coaster idle problem off and on ever since I bought the friggin' car last year - it goes away for a month sometimes, then comes back for two weeks or so. At cold idle, everything's perfect; take it down the street and as soon as things warm up, it'll start rolling up to just under 1000 rpm and then dropping down as low as 200 rpm at a stoplight, and sometimes even stalling. Tapping the gas wakes it up instantly - it doesn't lug and chug if you touch the throttle - so it doesn't feel like a fuel delivery issue, more like a sensor issue ... hence the trouble code for the EVP, I guess.

The weirdness is, aside from the fact that the EVP on there is new (along with EVERYTHING underhood ... and I mean EVERYTHING), I'm getting proper voltage to the wiring harness, and there's no broken/rubbed-through/split/frayed wiring anywhere on or near it. Unless it's something inside the connector, itself, that's turning loose and only doing so periodically, I can't seem to find anything wiring-wise that would cause this.

I've read some stuff about folks having to file the end of their EVP plunger or otherwise modifying it for whatever reason to make it cooperate with everything else. Any ideas?

Also, would the EVP being out of range or otherwise not functioning correctly result in that exhaust backfire I would sometimes get from WOT shifts from 1-2 and 3-4? ... maybe the EGR not closing off properly and/or otherwise causing an overly rich mix at WOT? Gas mileage is about where it should be (between 16-18 in town), too.

Any suggestions much appreciated. I wanna have this beast in tippy-top shape before I hit the track next month.

 

[jrichker]

CODE: 31 (KOEO) - EVP circuit below minimum voltage. Vref (5 volt reference voltage supplied by the computer) missing or broken wire or bad connection in circuit. Use a DVM to check for 5 volts on the orange/white wire. If it is missing, look for +5 volts at the orange/white wire on the TPS or MAP sensor located on the firewall near the center of the car. Use the black/white wire for the ground for the DVM.
With the sensor removed from the EGR and still connected, press the plunger and watch the voltage change on the brown/lt green wire. Pull the passenger side kick panel and measure the voltage at the computer. You will need to remove the plastic cover over the wires and probe them from the backside. A safety pin may prove very useful for this task. Use pin 27, EVR input (brown/lt green wire) and pin 46, signal ground (black/white wire) to measure the voltage. The orange/white wire is Vref and should always be 5 volts -/+ .25 volt. Be sure to measure Vref at the EGR sensor to rule out any broken wires or bad connections.

You'll need to have a voltmeter in hand to catch it when it misbehaves. That is the only sure way to catch this problem. A broken wire or intermittent connection would cause this type of problem.

 

[JChalfan]

I had a code 31, EVP voltage below min. I replaced it with a brand new NAPA EVP sensor, which turned out to be defective.

I would suggest using a multimeter to check the EVP. Here's a past post by jrichker where he details how to check the sensor with a meter:

http://forums.stangnet.com/showthread.php?t=615689

BTW, JRICHKER, thanks a lot for the above post, very informative.

When I checked my brand new (defective) one, the resistance readings were correct when the valve was all the way open or closed. However, when I slowly moved the plunger in and out, I saw the resistance spike on the meter sometimes. This was tripping my CEL and storing a code 31.

I didn't have a surging idle as a result, so that may be unrelated.

Hopefully this will at least help you rule out a faulty sensor. New parts don't always work right.


Jeff

 

[petr1]

I have 91 gt and my check engine light is blinking randomly during drive. There is nothing else wrong, car drives well and idle is good. I pulled codes and I get 31. what would it be. It feels like there is nothing wrong whit it but cel blinks. Engine is stock by the way.

 

[Darkwriter77]

It seems I must have a bum sensor, then. As I said, EVERYTHING underhood is new (except the fuel pressure regulator ... which I'm swapping out sometime this month, just on principle), and the EVP was one that I replaced at the same time as the EGR. I'm not entirely sure that my old one was bad at all, so I'll try swapping it on and see if it trips the code, too. (All the more glad that I keep all my old sensors as spares in the trunk. )

 

[petr1]

I put new EGR valve and sensor and now it's working.

 

[TENGRAM]

It seems I must have a bum sensor, then. As I said, EVERYTHING underhood is new (except the fuel pressure regulator ... which I'm swapping out sometime this month, just on principle), and the EVP was one that I replaced at the same time as the EGR. I'm not entirely sure that my old one was bad at all, so I'll try swapping it on and see if it trips the code, too. (All the more glad that I keep all my old sensors as spares in the trunk. )

when i did my FPR, my roaming idle went away, not because of the FPR but because of the new gaskets and better seal on the intake manifold. i guess i had a vacuum leak . i hope you have the same results, good luck

 

[globaltefl]

Is 4.7 reference voltage too low a reading on the EGR/EVP sensor? I know it is supposed to be 5 volts.

 

[HISSIN50]

Is 4.7 reference voltage too low a reading on the EGR/EVP sensor? I know it is supposed to be 5 volts.

Should be fine.

 

[kpack5982]

Maybe check the gasket that connects it to the egr on the back. I was getting code 31 and 33 every now and then and turns out the gasket wasn't on there right and after i sealed it on, I haven't seen the codes since

 

[strtrcr50]