91 Legacy Code 24? Bypass air control solenoid

[Gloyale]

I am getting a persistant code 24 on a 91 Legacy.

 

I tested resistance of the solenoid. Good.

 

Swapped with on from a car with no codes, no change(measured same resistance as the first)

 

Checked all harness for continuity on each wire end to end. From engine to ECU, each section of harness at a time. Also checked for any continuity to other wires or ground, checks out good.

 

 

Still, this code 24 persists. In addition, I am occasionally getting a *31* TPS code.

 

And to make it more confusing, The TPS was adjusted so that the idle switch never closes. If you set it properly, it tries to die as soon as the idle switch closes. Also, the *do not adjust* screw has been adjusted.

 

 

What do ya'll think. Could an improperly adjusted Throttle body cause the ECU to be so out of whack trying to control idle, that it would set these codes? My guess is no. I still anticipate finding an elecrical issue. Any ideas appreciated though.

[OB99W]

See section "Legacy and Impreza Engines with No Injection Pulse #1 Cylinder" in:

http://endwrench.com/images/pdfs/Emissions.pdf

 

I wonder if the ECU thinks there's an IAC problem, and would be shutting off the #1 injector (as described in the article), except for the idle switch not closing due to the misadjustment. Perhaps checking whether #1 is pulsing correctly, especially if you allow the idle switch to close, might provide a clue. (Yeah, it's just a guess, I haven't run into the specific problem you've described.)

[Cougar]

Since you have a good circuit to the solenoid it would appear the ECU is the problem.

[Gloyale]

Since you have a good circuit to the solenoid it would appear the ECU is the problem.

 

Yeah, I found this thread from Phiz and the ECU was apparently the problem http://www.ultimatesubaru.org/forum/showthread.php?t=72794&highlight=code+24

 

 

However, he didn't have the idle and TPS issues i am seeing. I am going to swap throttle bodies to one that has not been tampered with and see what we get.

 

I need to pull vacuum and compression readings from the motor to make sure we don't have a mechanical problem.

[Gloyale]

See section "Legacy and Impreza Engines with No Injection Pulse #1 Cylinder" in:

http://endwrench.com/images/pdfs/Emissions.pdf

 

 

text from that article:

 

Legacy And Impreza Engines With

No Injection Pulse #1 Cylinder

Built into the fuel injection control

unit is logic that will shut off the #1

injector if the computer believes that it

can no longer control the Idle Air Control

Valve. Remember this design characteristic

if you are trying to diagnose a “hard”

code for the Idle Air Control Valve or a

dead miss in the number one cylinder

due to no injection at idle. A problem in

the Idle Air Control Valve circuit may be

responsible. (Component testing shows

that it most likely is not the valve itself.)

Also, if the computer is deprived of its

“back up power supply,” some computers

will generate a false code for the Idle

Air Control Valve and kill the injector for cylinder #1. The pin location of this

power supply can be found in the Control

Unit Module I/0 Signal pages of the

appropriate Service Manual.

 

 

 

Very useful.

[Gloyale]

Think I just solved it.

 

I believe the engine was swapped with one from a Manual trans car. Problem is that manual and Autos have different Bypass Air control valves. Autos have 3 pins on the valve, and Manuals only have 2. Both have the same 3 wires in the Engine harnes but the valves have very different operations. Auto valve can be forced open and closed, IIRC manual valve can only be closed.

 

Swapping valves in a minute. Results and the diagrahm that led me to this to be posted soon.

[Gloyale]

That was it!!!

 

The car had a swapped engine in it. One from a Manual trans vehichle. The Auto ECU was looking for the 3rd pin on the Bypass Air Valve which the auto style don't have. Installed the 3 pin valve (have to swap the whole valve body, not just solenoid) Code gone, misfire gone, idles beautifully.

 

 

What makes this more interesting is that The 92 Legacy FSM PDF file I have, does not show that difference in the diagrahm. It gives one schematic for all models. It was when I went back and looked in my hard copy of the 90 FSM that the difference is illustrated with seperate diagrahms and flowcharts for diagnosing this code 24 for Manual vs. Auto. Scanner isn't working now or I'd post the diagrahms.

 

So for anyone out there using the 92 Leg.FSM PDF file, you may want to try to get a 90 or 91 book. Seems they reformatted and omitted some stuff in the 92.

 

Also, as a note, I discovered some sizable differences in wiring colors and pin arrangements between the 90-91 cars and the 92-94. So if you are relying on wiring diagrahms to trace problems, you really need the correct book for you're year.

[Olnick]

Code gone, misfire gone, idles beautifully.

 

I just love to read something like this in a post!

 

Way to go Gloyale, good detective work. And thanks for sharing what you learned--for sure it'll help someone else down the road.

[Cougar]

Very good detective work Gloyale and thanks for the info.

[OB99W]

That was it!!!

 

The car had a swapped engine in it. One from a Manual trans vehichle. The Auto ECU was looking for the 3rd pin on the Bypass Air Valve which the auto style don't have. Installed the 3 pin valve (have to swap the whole valve body, not just solenoid) Code gone, misfire gone, idles beautifully.[...]

That certainly explains why the diagnosis wasn't obvious, based on the code.

 

Congrats, and thanks for the follow-up.

[Hondasucks]

I wonder if that's what's wrong with my 90? I've swapped in like 4 different valves, and I get the same code, I ended up adjusting the valve manually with the two screws on the top in order to get a 900 rpm idle. I discovered by plugging the select monitor in, the "IAC duty ratio" goes to 100%, and it's supposed to be 40-50% at idle. I discovered a bent pin in one of the engine harness connectors, I think that's my problem but I haven't gotten around to swapping the engine harness out yet lol.

[Gloyale]

I wonder if that's what's wrong with my 90? I've swapped in like 4 different valves, and I get the same code, I ended up adjusting the valve manually with the two screws on the top in order to get a 900 rpm idle. I discovered by plugging the select monitor in, the "IAC duty ratio" goes to 100%, and it's supposed to be 40-50% at idle. I discovered a bent pin in one of the engine harness connectors, I think that's my problem but I haven't gotten around to swapping the engine harness out yet lol.

 

 

Well, it's easy to tell. If it is a Manual, the solenoid on the valve should have only 2 pins. If it is an Automatic, 3 pins.

 

I would assume it's actually more important to match the ECU, than the actual trans. (ie. you could swap in a 5 speed, but as long as you kept the auto ECU, you'd keep the auto Valve/solenoid)

 

I have a spare manual (2 pin) valve if you need one.

[Hondasucks]

So the manual valves actually only have two pins? EVERY valve I've swapped in has had three pins... (but different part numbers)

I did NOT want to spend $180 on a new valve (and that's WITH my discount!) What do you want for it? I have a huge pile of Subaru parts...

[Gloyale]

Hey HondaSucks, I was curious if swapping in that 2 pin valve made any difference?

 

After more research, it seems this difference between auto and manuals was particular to 90,91. Seems all the 2.2 engines I've seen 92 or later have 3 pin valve. That would explain why none of the later literature mentions a differnece, but it seems the ECUs from those 2 early years need to have matched valve bodies and solenoids or they will throw codes.