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Old 03-27-2003, 07:43 PM   #1
Ramsdale
Scooby Newbie
 
Member#: 1951
Join Date: Jul 2000
Chapter/Region: NESIC
Location: NH, CT, hotels...
Vehicle:
08 M3

Default Idle problem - Info only

Just posting this in case it helps anyone out who is searching for info on idle problems:

Car = 1999 Impreza RS. No intake or engine mods. 50,000 miles. No oil leaks or any problems with head gasket.

Issue = When the engine was warm, it would nearly stall when the car was stopped. At speed, the engine ran fine, and when in neutral coasting to a stop, it would drop to normal idle and stay there for a moment. However, once the car came to a complete stop, the idle would drop to about 200 rpm and the motor would nearly stall. Then, it would catch itself, rise up to about 1000 rpm, drop again, and so on until it balanced at about 4-500 rpm (which was a low idle).

If the engine was turned off and restarted while still warm, it would start up just fine, but would then almost immediately stall as above.

When cold, the engine would idle high (as is normal) and would have no issues on restarts. Likewise, the motor was fine at speed, under load, etc. No missing, pinging, hesistation or any other abnormalities.

It did this for a couple of weeks, and didn't seem to get worse or better. During that time I tried...

Things that had no effect = New air and fuel filter (Subaru OEM parts). New spark plugs and wires (NGK as listed in manual). Changed the oil and filter while I was at it. Checked air intake plumbing for leaks (none), and checked all vacuum lines for leaks (none). Tried fuel ejector cleaner and switched brands of gas. Checked PCV and EGR valves (working properly). Tried sacrificing an old Rochester Quadrajet to the Gods of Lumpy Engines, asking them to bless the Subaru with smooth operation once again, but no effect.

Dejected, but with the Spring tune-up out of the way, I headed off to the local Subaru dealer to have them take a look, and to get the new MAF sensor per a recall notice I got in the mail.

Yes, what it was = Bad MAF sensor. I had read lots of posts about how when the MAF sensor goes bad, the car goes into limp mode. Since I could happily run the motor to redline, I figured it was some weird vacuum problem I couldn't trace, or some odd engine management problem with the computer. Nope, turned out that they just slapped a new MAF on, and the problem went away. At least the little line at the bottom of the worksheet said "$0.00 - Recall Item"

So, just in case someone else is having the same issue, with a '99 RS, don't rule out the MAF just because the car isn't in limp mode.

(Disclaimer: If you have missing/surging/hesistation/knocking/rough idle/wild mood swings - you are probably looking at something else. Also, if this is your first Subaru and you just got it - yes, the idle is a little rough normally. Don't sweat it.)

Enjoy,
KR
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Old 03-28-2003, 12:46 AM   #2
m750
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Member#: 2278
Join Date: Sep 2000
Chapter/Region: NESIC
Location: Pepperell MA
Vehicle:
8Sti | 07 allez
White | Comp

Default

I've had very similar results w/ a bad 02 sensor.... Tho, passing the info on is always appreaciated...
AO
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Old 03-28-2003, 01:04 PM   #3
Ramsdale
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Member#: 1951
Join Date: Jul 2000
Chapter/Region: NESIC
Location: NH, CT, hotels...
Vehicle:
08 M3

Default

--bonks head--

Yup, I forgot to mention the O2 sensor as another possible culprit. Thanks for mentioning that one.

As anyone doing a search will see, there are a lot of possible causes of idle issues. Since some people may not associate the MAF with idle problems, I wanted to give some specifics on how the car was acting.

KR
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