Code 24 - IAC problems - update: reproducible

HappyFrog · Post by **HappyFrog** » Sun Aug 16, 2009 6:11 pm

I have an odd problem with the IAC. The car idles fine, but while driving CEL comes up once in a while and stores a code 24.
I cleaned the IAC which helped a lot, but there are still problems. I can't provoke the error and it comes on out of the blue. On my way home from work it failed during WOT at one time and again while cruising through town at a steady 30mph.

If I let go of the throttle and step on the clutch, CEL goes away immediately. If I stay in gear or stay on the throttle CEL stays on.
While CEL is on it pulls really bad and it fuelcuts if I go above 4k revs.

I'm beginning to suspect the problem is somewhere else, but I have no clue where to look. I have 25 miles to work, on my way in it didn't show up and on my way home it showed up a couple of times, so there is absolutely no pattern in when it fails.

Is there any difference between the green labeled IACs btw? I can't find a used one with my p/n and the local subaru dealer would not sell his (I guess, the price was ridiculous).

HappyFrog · Post by **HappyFrog** » Thu Aug 20, 2009 6:17 am

No problems this morning after another good cleaning, odd.

I found a nasty leak in the pressure system btw. After I fixed it the turbo spools at least 250 rpms earlier... Cheapest optimization I ever did

HappyFrog · Post by **HappyFrog** » Fri Aug 21, 2009 6:34 am

Well, problem returned yesterday afternoon. I found a way to reproduce it though, just let go of the throttle while in gear and CEL comes on somewhere between 1200-1700 rpms.

ericem · Post by **ericem** » Fri Aug 21, 2009 6:36 am

Did you clean your IAC by removing the top part, then spining the shaft while spraying intake cleaner down the pipe till the shaft spins smooth?

HappyFrog · Post by **HappyFrog** » Fri Aug 21, 2009 6:42 am

Yup. The inside of the top looked brand new btw, and the shaft kept spinning with ease, so no problems there either.

Resistance in the IAC and voltage with engine on is also ok.

n2x4 · Post by **n2x4** » Fri Aug 21, 2009 1:17 pm

Sounds like your car is pulling timing to me. Try connecting the green test connectors under your dash and see if it behaves any differently.

HappyFrog · Post by **HappyFrog** » Fri Aug 21, 2009 4:12 pm

I'll try that, thanks. I've also been suggested to clean MAF and check the TPS.
Read somewhere a dirty BPV could throw code 24 as well, so plenty of places to look

Post by **Legacy777** » Mon Aug 24, 2009 2:57 am

Did you install the top portion of the IAC valve in the exact same position as before you removed it?

It sounds like the IAC valve is throwing a duty cycle that is out of the specified range, and causing a code.

You could check the IAC duty percent with the Vikash's scan tool, and report what number you get.

HappyFrog · Post by **HappyFrog** » Mon Aug 24, 2009 6:19 am

"Exactly" depends on how sensitive it is

There where marks after the screws though, so yes I'd say it was close enough. Is it possible to monitor the signal by either voltage or resistance?
I haven't seen a portable with com or parallel ports the last couple of years, so I can't really use the diy connector.

Maf and bpv was ok by the way.

SLODRIVE · Post by **SLODRIVE** » Mon Aug 24, 2009 5:26 pm

Check the idle switch setting on your TPS, if you haven't done so already. That played a part in my odd IAC issues right after my engine swap.

Post by **Legacy777** » Mon Aug 24, 2009 6:50 pm

HappyFrog wrote:"Exactly" depends on how sensitive it is There where marks after the screws though, so yes I'd say it was close enough. Is it possible to monitor the signal by either voltage or resistance?
I haven't seen a portable with com or parallel ports the last couple of years, so I can't really use the diy connector.

Maf and bpv was ok by the way.

As slodrive mentioned, check the idle switch first.

You can monitor the PWM percentage with Vikash's scan tool and see how it compares to the specified ranges in the FSM.

http://bbs.legacycentral.org/viewtopic.php?t=24376

HappyFrog · Post by **HappyFrog** » Mon Nov 02, 2009 3:29 pm

It turned out to be TPS problems, I got a used one from a 95 STI and it seems to be working.

One week ago the problem got worse and while cruising the engine would suddenly stall without CEL or it would fuelcut every other time during WOT. The TPS seems to be measuring what it should so perhaps it was bad contact with the plug or something.

I've just spent the last hour beating the crap out of it and it didn't fail once - yes, I'm still grinning, it was nice to finally see it pull all the way to redline over and over again

HappyFrog · Post by **HappyFrog** » Mon Nov 02, 2009 3:37 pm

Oh, right another thing, as slodrive mentioned about odd IAC issues, setting the TPS to too low idle rpms will cause a code 23 (bad MAF voltage).
If I set it to ~800rpms CEL came on every time I was about to stop. Setting it a bit over 1000rpms and it never came up... weird stuff. I'll try to adjust rpms by turning the IAC head instead, 1000rpms seems to be a bit high.

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Code 24 - IAC problems - update: reproducible

Code 24 - IAC problems - update: reproducible