I'm going to assume that this test was performed when the motor was
cold..... giving the IAT and ECT (codes 21 and 24) readings are out of self
test range. To eliminate these as concerns, we would run the motor to
operating temp and rerun the KOEO test....
To address the memory code, we would need to perform the KOER test to see if
we are dealing with a hard fault or an intermittent.... At any rate, the
most likely cause for code 31 would be the EVP sensor on top of the EGR
valve. Pay attention to "most likely"....
These "ancient" electronic control systems offered relatively little in the
way of self diagnostic capabilities. Occasionally, parts replacement can be
considered a viable diagnostic step... especially if testing the sensor
would cost more than replacing it.
At the same time, it is important to pay attention to the base engine....
particularly the fuel filter which seems to be often forgotten.
While I am trapped to using the 1992 PC/ED (the oldest available on CD), the
link supplied by the other respondant appears to contain some
You are correct. The codes 21 and 24 went away when
warm. But the 31 remains. The car now is idling at a loping gate when cold,
but ok warm.
I mean ok/stumbling at about a 5 second rate each. Sounds like something
leaking air in, like the PCV or EGR.
I checked the PCV and it seems ok. A little leakage in the closed direction.
Probably time for
a new one of these. It has never been replaced. Also, It looks like I will
have to take the EGR out and clean it or replace it.
I have been getting a code 31 lately. Idles bad cold and stalling. So today
I changed out the PCV valve, the EVP position sensor on the EGR, and the
gasket on the EGR valve. All three seemed ok before changing but I changed
them anyway. The problem remains. EGR looks ok (sealing well with no
vacuum). I cleared out the saved code 31. Now I will see what saved code
turns up next.
Anyone have any other ideas?
'89 LX 3.0
Run KOEO (key on engine off self-test) and see if any on-demand codes show
Check that the position sensor receives VREF (+5V).
If you have VREF, the EVP signal (the wire that's neither VREF nor GND) may
be open somewhere between the sensor and the processor (computer). Take a
good look at the harness connector for the sensor. It's easy to damage
contacts by pushing a probe into them.
If at some point the processor (computer) has been removed and the harness
probed, the same problem might exist at the other end. Make sure that both
EVP and VREF contacts look good. These are frequently intermittent. My LTD
used to stall in hot weather. By the time I got to test things, everything
looked right. Finally I caught the entire VREF line at 0V when the engine
stalled - a poor contact at the processor end. No output from every single
sensor that uses this reference.
Don't know what type of connector you have at the processor end. On the
3-row variety, the relevant pins are typically 26 and 27. Use an EVTM manual
(or perhaps Alldata at the library) to find the connector pinout for your
Finally, there is always a chance of a defective processor, unable to read
the EVP signal. Least likely, but not impossible.
I checked the VREF and I have the 5 volts. I then ran the
car a long time in the yard. No code 31. Idle ok after
I have a hunch its the fuel filter in front of the gas tank. Its never been
replaced, but the fuel pump in the gas tank has. Maytbe its clogged and
affecting the idle cold.
That's good news.
I doubt that poor idling would be caused by restricted fuel delivery -- the
demand is very low. One reason could be a defective idle control (most
likely a throttle bypass valve, but not sure what type your engine uses).
Another could be a shorted ECT (coolant temperature sensor), erroneously
indicating that the engine is warm.
These older EECIV processors have a somewhat limited self-diagnostic
capability, but before acting on any guess and throwing parts at the
problem, I would run KOEO (with the engine cold), then warm it up and run
KOER. Very simple to do and you may learn something useful from the
Well, the problem is still the same. Ran all the codes and
they all come up 11 now (ok). Still a galloping idle when cold. Looked at
everything I can see but everything looks ok.
If I put in in gear right away when cold with the brake on and give it some
gas it likes that after. I wonder if its something major like the timing
Found the problem. I took off the hose from the air
cleaner to the throttle body and found
the throttle plate very dirty. After a thorough cleaning the idle went way
up. This was probably from me fooling with the base idle screw over the
years. Then I cleaned the idle air bypass valve (also very dirty but not
stuck). Finally I reset the base idle and TPS voltage. Now the motor purrs
like a kitten!.
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