12 replies to this topic

[mcmastai]

Hi everyone;

I've been lurking forums for ages trying to find an answer to this problem, but I have finally decided to try and get to the bottom of it myself. I bought my '00 JDM Legacy GT-B (BH5 with the EJ206) about a month ago, and I've been chasing this issue ever since.

Basically, the car keeps throwing Code 24 (IACV malfunction) along with a check engine light. When it does this, revs sit at around 1400 and the ECU cuts fuel to cyl#1 causing the car to run on 3 cylinders. If I shut off the car, it usually "clears" the CEL and it will no longer be running in limp mode. Although the condition will return, uusually when the car is in park and the revs return to idle. However, I noticed the condition also goes away when the A/C compressor kicks in. Basically I can clear limp mode and the CEL just by cycling my A/C on and off.

I have pulled the IACV and thoroughly cleaned both it and the TB, and made sure the valve is cycling smoothly and properly. When I unplug the MAF when idling the idle gets super lumpy like the car is about to stall, making me think the MAF is good as well.

Additionally, my idle is unusually high, sitting anywhere between 1100 and 1400, and I'm getting extremely poor gas mileage (~350km to a tank). Also, on cold starts, the car will idle extremely low (1-250rpm) for a few seconds before jumping to 2000rpm, hunting for a moment, and settling in at ~1200rpm. When the idle is low, pressing the gas does not help in the slightest making me think it is running extremely lean.

In conclusion:
-car throws intermittent CEL with code 24 and limp mode. Clearable by cycling A/C.
-car has low idle on cold starts (1-200rpm)
-extremely poor gas mileage (350km to a tank)

Any help is appreciated, or if you could give me some hints of what else I could look at and try. I am planning to take the car to my tuner sometime in the next couple weeks to get the vacuum system leak tested, but other than that I am kind of at a loss.

Thanks!

[duncanm]

Well - the AC does change the idle speed, so that may give some clues

[mcmastai]

Boost gauge ?
Do you know what vac it sits on at idle?

As for the A/C reset... that is some weird arse shit and I do believe your car is haunted, run!

 

I haven't got a boost gauge, but I am planning on picking one up in the near future. Not sure what it sits at at idle, although had the system tested last week. One cap had blown off under the plastic alternator cover, but other than that it is pretty good; no major leaks and running smoother.

 

Sadly the problem still persists. My tuner thinks it's something to do with the wiring, since the misfire and CEL goes away when the fans come on. I thought it was only when I hit the button, but I realized it happens when there is a little extra load from the fans. 

 

I'm thinking about looking at the cam and crank sensors, as well as the engine temp sensor and lambda (replacement on the way). Although my gauge is working fine so I really don't see how that would cause much of an issue. 

 

This morning I think I'll go out and wiggle the engine harness about and see if I can find an intermittent short ha ha, honestly at a bit of a loss. Will report back!

[mcmastai]

How did you find out it was a code 24?

Scanned or did you use the green plugs?

And that is the only code showing right?

 

I used the black plugs actually, but I'm thinking it's time to pick up a VAG-KKL and hook it up to FreeSSM. Yeah, 24 is the only code showing. I gave the MAF and TPS a clean last night on the off chance that something fishy was going on there but it had no effect as expected. 

 

Could it possibly be the engine sensor relay? I was reading on another forum that a guy was having issues where a sensor was throwing a code but had no signs of malfunctioning, and what it turned out to be was the engine relay wearing out and providing a lower voltage than what was needed. Although, I can't think of a reason why the fans turning on resets the code... It idles really high as well, ~1400rpm, thinking that if I find the source of the high idle I will also find the source of the malfunction. Could it be that the idle isn't reducing from the High Idle mode that is supposed to be initiated when the AC fans turn on, making the ECU think that it can no longer control the idle using the IACV? Then when the fans turn on it thinks everything is OK again because the idle is where it is supposed to be for the given circumstance. 

 

Absolutely outrageous haha. 

 

09/26 UPDATE: Ruled out the IACV for sure by replacing it with a known good one, just to put my mind at rest. Had an odd instance today where instead of my A/C turning my CEL off, I brought on the CEL by applying my brakes (preparing to shift into R). It turned off again when I released them. It is almost certainly an electrical gremlin at this point; I'll be doing some more investigating whenever I have a chance this week.

 

I'll keep updating as I go in the chance that I might help someone one day with similar issues.

 

09/28 UPDATE: I found the wires coming out of the O2 sensor to be entirely frayed and shorting on each other. There was no continuity between any of the three wires. I have a new one so I'll be replacing that tonight. Praying that this, for some reason, is the source of all my troubles. 

 

Predictably it wasn't. Replaced both the sensor and the wiring anyway, but there's been no change otherwise. Really running out of ideas here, thinking about just swapping the ECU and hoping it fixes the problem.

 

10/06 UPDATE: Figured out my vacuum lines are missing restrictor pills and are on in the wrong configuration. I'll most likely be fixing them tomorrow, looking for a 2mm orafice/restrictor pill part number.

[mcmastai]

BUMP UPDATE: Got some snazzy new Vac lines on the way, just have to wait for them to arrive. Still feel like no one else on the internet has encountered this before haha

[mcmastai]

Bump, issue is still there after fixing vac lines. Anyone have any tips?

[mcmastai]

Good news everyone! 

 

The car is fixed. The issue was a previous owner had cranked the idle screw way out, so the throttle plate was being held open way too far. Simply set it back to spec and all symptoms disappeared!

[duncanm]

good to hear its sorted - its always the simple things.

 

When you say idle screw -- I thought these went the way of the dinosaurs.  Do you mean throttle cable adjustment?

[Barbbachello]

My car has an "idle screw" not what its for i assume but there is a screw you can use to crack the throttle

[mcmastai]

good to hear its sorted - its always the simple things.

 

When you say idle screw -- I thought these went the way of the dinosaurs.  Do you mean throttle cable adjustment?

That is exactly what I mean, sorry, didn't know there was a difference!

[mcmastai]

That is exactly what I mean, sorry, didn't know there was a difference!

 

Just thought I'd follow this up and clarify for anyone reading in the future: by throttle cable adjustment I do not mean the tensioning screw with a bolt on either side, like 100% of the other threads on this I've read use. The screw I adjusted actually adjusts how far the throttle plate within the throttle body is allowed to close, by stopping the rotational bracket the throttle cable is locked into from turning. Look on the lower throttle cable side of the TB on the back side (closest to the firewall). The screw will be very small, but it will be clear what it does.