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Old 07-20-2019, 12:48 PM   #1
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surging at idle

97 boxster with 33K miles. I recently changed the oil and filter. A day or two after this job, I notice the engine surging at idle - dropping down to about 300RPM then jumping up to maybe 1100 RPM, but it idles normally about 50% of the time. Sometimes it surges, sometimes it doesn't.

Turning on the A/C bumps the idle up to about 700 RPM and I haven't noticed any surging with the A/C on.

I checked the oil level and noticed that it is a little above the full mark.

I don't know if this is coincidence with another problem or related to the oil change.

Doing some searching about the surging and the most cited answer is to clean the TB and replace the Air Oil Seperator (AOS). I just don't want to throw parts at it, so how can I tell if the AOS is defective?

I will, however, remove and clean the TB as it has never been done.
Insight? Suggestions? Much appreciated.
J

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Old 07-22-2019, 05:20 PM   #2
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This reply wont be of much help.....but my new to me 01 box base with high mileage surges at idle when AC is on........and does not when AC is off. I will be interested in what is causing your issue.
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Old 07-22-2019, 05:59 PM   #3
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This reply wont be of much help.....but my new to me 01 box base with high mileage surges at idle when AC is on........and does not when AC is off. I will be interested in what is causing your issue.
When time permits, I'll clean the TB and will try to report back the results here.

If the TB on your vehicle hasn't been done in while, it probably would be a good idea to clean it. On my jeeps, cleaning the TB every 30k-40K miles was a well known std practice to guard against bad engine performance.

Am actually surprised that no one has provided any comments to the original post.
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Old 07-22-2019, 07:14 PM   #4
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Well I have to replace my starter soon....so while I have the TB off it will get a good cleaning. Good luck with your scenario.....hope ya get it fixed.
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Old 07-22-2019, 08:57 PM   #5
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Originally Posted by boxster_nut View Post
97 boxster with 33K miles. I recently changed the oil and filter. A day or two after this job, I notice the engine surging at idle - dropping down to about 300RPM then jumping up to maybe 1100 RPM, but it idles normally about 50% of the time. Sometimes it surges, sometimes it doesn't.

Turning on the A/C bumps the idle up to about 700 RPM and I haven't noticed any surging with the A/C on.

I checked the oil level and noticed that it is a little above the full mark.

I don't know if this is coincidence with another problem or related to the oil change.

Doing some searching about the surging and the most cited answer is to clean the TB and replace the Air Oil Seperator (AOS). I just don't want to throw parts at it, so how can I tell if the AOS is defective?

I will, however, remove and clean the TB as it has never been done.
Insight? Suggestions? Much appreciated.
J
Check your oil fill cap? Maybe its not on right, or its cross threaded.

Also to check your AOS -- you can undo the oil fill cap and see if there is a suction on the fill tube. If so, that's usually an indication of an AOS issue.

The other possibility is clean the MAF.

Mike
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Old 07-22-2019, 09:44 PM   #6
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Mine was the MAF... cleaned, good to go. Worth a quick shot.
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Old 07-23-2019, 06:19 AM   #7
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Also to check your AOS -- you can undo the oil fill cap and see if there is a suction on the fill tube. If so, that's usually an indication of an AOS issue.
No suction on the oil fill cap when running is an indication that there is an air leak in oil fill tube. There should be suction, but not enough to prevent you from unscrewing the cap. If you cannot unscrew the cap when the car is running its an indication that the AOS is bad.

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