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Old 10-23-2000, 07:09 AM   #1
rjones
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Join Date: May 2000
Location: Cambridge, MA
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2003 wrx wagon
silver

Post Fliter Gasket, Whimpy MAFs, & idle

I just fiddled with the intake of my MY99 by installing a K&N, replacing the second filter with a gasket, and removing the fender 'snooter.'

I did a thorough ECU reset, and the car runs strong. BUT... it constantly idles at 1500 for a few seconds at every stop now, even when the car is warm.

After doing a search, could it be that the second filter was there to damp pulses returning from the engine to the MAF sensor, and now without that filter the MAF is making it idle funny?

Any suggestions? (BTW I'm also running a brospeed exhaust)

Cheers-

RJ
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Old 10-23-2000, 07:14 AM   #2
STiShawn
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Smile

My car did this to after I removed the intake snorkus from the fender. After driving it after the initial ECU reset, I stopped the car, turned it off and then restarted it. It hasn't done it since. If it continues to do it, try one more reset. Us 99 owners need to stick together.
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Old 10-23-2000, 07:39 AM   #3
Rich L
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Post

Yes, please post your progress.
I own a 99 as well, with the stock intake.
Im too poor/stingy to get an intake with SAFC and too much of a chicken-***** to risk a lean running engine.
*Come on tuners! We need a good solution!*
Any info appreciated!
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Old 10-23-2000, 10:04 AM   #4
Scooter
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rjones,
I would have to say no, because some MY99s did not come with the second filter. If the second filter was needed to damp pulses, then Subaru would have put it on all MY99s. Plus the pulses wouldn't exceed much more than 200 Hz, and the filter media wouldn't do much at dampening stuff that low or lower.

How much oil did you spray on that K&N? I believe there was a Subaru of Canada TSB on oil from such filters causing problems with the MAF . That is one of the drawbacks of hot film MAFs. They don't have a burn off cycle like most hot wire MAFs have for burning off such contaminants. Hot film and hot wire MAFs work on the principle of forced convection cooling. As air flows over the heated element, cooling takes places. Anything (like a thin layer of oil)that would change the thermal resistance between the heated element and the air would cause an error. Important Note: The stock filter is an oiled paper element.


[This message has been edited by Scooter (edited October 24, 2000).]
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Old 10-23-2000, 10:17 AM   #5
ColinL
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The high idle is normal after a high vacuum, low-throttle cruise.

Are you absolutely certain your car didn't do this before? I thought my 99RS has always done it, but then again I swapped out the 2nd airbox filter for a gasket in the first few thousand miles so I can't specifically recall the early days.
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Old 10-23-2000, 10:25 AM   #6
Revision
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My 99 did come with the second filter. And I did replace it with a gasket and k&n filter. An ecu reset takes about 30 minutes to be safe. Start the car, let it idle for a few minutes and shut it off.

I had NO problems with wierd idle. Check the connections to the MAF and also check the hoses connected to the large plenum air box.
Make sure there are NO LEAKS.

The second filter is not really there to dampen pulses, thats what the box and the tubes shooting off the intake are for. I have a feeling the second filter is actually there to soak up the excess oil coming up from the breather hoses.

For those of you who want a tube intake, but do not want to buy an AFC, you can run the tube intake with a mod suggested by 8Complex.

Basically, using experimentation and observation vs an A/F meter. We were able to determine that the engine only runs lean at WOT at 5300 rpm. If you use part throttle, there is NO lean run condition even to 6500 rpm. The mod is simple. Stick a small 1" block of wood under the accelerator, then you can't accidentally run lean.
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Old 10-23-2000, 10:45 AM   #7
Rez
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Rally Blue Pearl

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I've got a MY99 RS and this has happened to me as well and a second ECU reset fixed it. Just to be sure, make sure the following is done:

1) Leave the battery disconnected overnight, sort of a 'just to make sure' method.
2) Reconnet (have keys handy if you have an alarm).
3) Start the car with EVERYTHING OFF (just to make sure)!!!! Do not touch the gas at all.
4) Let it idle for at least 15 minutes. I leave mine idling for almost a half hour, again 'just to make sure'.
5) Shut car off. Take keys out ('just to make sure') and restart.
6) So for a spirited drive and rev up to red line a couple of time to give the ECU a max range to calculate with.

Personally I like to use second gear and I run at ~5500-6250 for a couple of thousand feet to make sure the damn ECU gets the 'right' figures. Be wary and VERY smooth on the gas at these RPM's and gear.

Also, when you do these spirited runs, don't be gas heavy when shifting. Make sure your foot is OFF the gas when shifting gears. If you don't, the ECU will know that theere is a bit of gas and you'll get the high idle.

Since doing this I have not reexperienced the problem.

Good luck.

-Rez
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Old 10-23-2000, 10:59 AM   #8
Scooter
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Hopefully Imprezer will have an extended section on OBD II in the FAQ. Understanding OBD II and the different modes of operation would certainly shed some light on things. Like Revision's observations for instance.

"Basically, using experimentation and observation vs an A/F meter. We were able to determine that the engine only runs lean at WOT at 5300 rpm. If you use part throttle, there is NO lean run condition even to 6500 rpm. The mod is simple. Stick a small 1" block of wood under the accelerator, then you can't accidentally run lean."

By keeping the throttle from fully opening you are most likely keeping the ECU from going into "Hard Acceleration mode. Hence, you're keeping it in Closed-Loop mode. In Closed-Loop mode the ECU attempts to maintain an A/F of 14.7, and it does this based on the Oxygen sensor. The MAF does not come in to play in Closed-Loop operation. However, the mass flow rate is used in Hard Acceleration mode. If I recall correctly, some members have posted in the past that it seemed like their cars accelerated harder at part throttle than at full. Well, if they had an MY99 and made modes to their intakes that caused the MAF to misread resulting in the lean run problem, then their cars probably would accelerate harder if the ECU remained in Closed-Loop operation.

There's also an Idle mode of operation. What rjones has noticed may simply be a delay in the ECU switching over to Idle mode. Once in Idle mode the mass flow rate signal from the MAF is used to maitain a leaner mixture during idling.



[This message has been edited by Scooter (edited October 23, 2000).]
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Old 10-23-2000, 04:08 PM   #9
Warp3
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89 MR2 (Ice Blue)

Cool

I, being a 99 2.5RS owner, have also recently delved into air intake setups. I'm trying to eliminate as many supposed issues as possible with my setup. I chose the Pipercross Forced Induction Filter Kit from RalliSpec (it's essentially a cone foam filter that bolts to your MAF piece). Supposedly it's one of the main filters of choice for rally cars in the UK. According to RalliSpec, Pipercross doesn't even recommend oiling the filter unless you are in particularly dusty conditions (e.g. Rallying). So that should take care of the "over-oiling" issue.

I've also left all the stock intake plumbing alone (including the intake plenum, tubing, that little appendix, etc.) in hopes of eliminating several other theories. I haven't had a chance to take pics of it yet but I will post them on my website when I do. RalliSpec included a fabricated bracket to secure the filter (later I plan to make a cold air box that doubles as the securing method for the intake). I'll let you guys know what happens.

I do know there is a noticeable power increase (especially in the mid-high RPM range) and a noticeable noise increase (no change at idle and cruise but under heavy throttle or high RPM it growls.) Don't get me wrong though, it's not horribly loud, it's perfect. (Just for scale, keep in mind I like my car quieter than most car enthusiasts.)

Shane "Warp3" Warren
1999 Subaru Impreza 2.5RS
http://jump.to/warpthree
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Old 10-24-2000, 12:32 AM   #10
rjones
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Post

Scooter's observation seems pretty good. When pulling up to a stoplight there is a period (5-10 secs) of high idle, and then there is a definite switch to a normal idle-- as if a new system or governor took over.

The downside is that this new delay in switching to the other MAF-controlled loop couldn't have been caused by a new filter. But perhaps it could be caused by a bad reset.

I'll unplug 'er tonight and we'll see if it continues.

thanks
rj
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Old 10-24-2000, 12:43 AM   #11
ColinL
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Well I've searched and searched some more but I can't find the original post, nor do I know who posted it.

However, it is normal for the ECU to idle around 1500 rpm after high vacuum cruise. Apparently it's an emissions thing, and I'm sorry I can't find the original post to provide more details.
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Old 10-24-2000, 09:32 AM   #12
KITTbri
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So i understand completely here, to reset let it sit for minimum 30min.
the filter media does not necessarily matter.
MY99's have two filters. i have a MY99 and could only find the main one in the box by the fender. Where would the second be? I have replaced the OE with a K&N. Now I need to reset? Does the OE induction constrict that much that a complete replacement is warranted? I thought the purpose of the fender box was to provide undisturbed, cold air to the intake, would not a cone filter then contradict that?
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Old 10-24-2000, 09:37 AM   #13
Warp3
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If your car has a 2nd filter it will be located in the big black box mounted on the back of the throttle body (directly under the hood scoop). Apparently only later MY99 cars had the 2nd filter (plus California emissions cars). If you don't have a filter there, you will instead have a gasket (to seal the box which the rim of the filter would normally do).
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