Strange Idle Behaviour

[pidj]

This being my first Porsche I would defer to you experienced owners. I have a strange idle behaviour once the vehicle warms up to operating temp: At stop, it drops to ~600 then bumps up to ~750 .... rarely it will kick up to ~1100 each time it returns to ~750. I have heard the MAF sensor mentioned in multiple posts dealing with multiple issues, but I don't know if this would be one of them. There is no smoke, no other symptoms. I use ethanol free Shell V Power petrol and STP Octane boost .... 2001 S .... everything stock.
I appreciate any thoughts on what this might be and the best was to troubleshoot.

Thanks!

[paulofto]

You may want to make 100% sure you have the correct MAF. They all look pretty much the same but their sensor characteristics have to be matched to your particular car. The 2000 year is a cross over year.

This is from the Pelican DIY article. Link here Porsche Boxster Mass Air Flow Sensor (MAF) Replacement and Troubleshooting - 986 / 987 (1997-08) - Pelican Parts Technical Article

Porsche Part # BOSCH Part # Application Notes
996.606.123.00 0-280-217-007 1997-99 All Boxsters Sensor for use with cable throttle cars
996.606.124.00 0-280-218-009 Early 2000 Boxster / Boxster S Original sensor for E-gas cars
(thru Boxster 2.7L Chassis #98 6YS 62 0414 and #98 0YU 62 5099)
(thru Boxster S 3.2L Chassis #98 0YS 66 0257 and #98 3YU 66 2413)
986.606.125.00 Mid 2000-04 Boxster / Boxster S First updated sensor for E-gas cars
(discontinued and replaced with version 125.01 below)
986.606.125.01 0-280-218-055 Mid 2000-04 Boxster / Boxster S Latest updated sensor
987.606.125.00 0-280-218-145 2005- All Boxster / Cayman Integrated housing design

[oldskool73]

Maybe also try cleaning the throttle body?

https://www.youtube.com/watch?v=slPzoplzWT0

[Anker]

And also check for vacuum leaks. They typically have the greatest effect when idling.

[pidj]

Because there was a fair bit of work done (below) I will test for a vac leak. I'm assuming this is a factory installed MAF, so it's either dirty (not cleaned when the work was done) or a clamp was not tightened properly/missed when reinstalling the throttle body and plenum.

"Cabin Air Filter: Inspected and replaced with charcoal embedded Mann filter

Engine: Inspected and replaced Mahle air filter. Hoses and belts inspected for cracks. Oil and oil filter replaced with Hengst filter and Mobil 1 0w40 Synthetic. New drain plug washer installed. Slight oil seapage between transmission and engine. Rear main seal was replaced during IMS retro kit install. Oil filter inspected for debris with none present.

Throttle body: Removed and inspected. Slight residue buildup on butterfly. Throttle body and plenum cleaned inside and out. Computer calibration completed.

Oil/air separator: No abnormal oil residue in throttle body or plenum.

Spark Plugs: Replaced with Bosch 7413 plugs.

Coil pack check: Inspected for cracks.

Engine bay check: Cleaned with damp rag and inspected.
"

[rexcramer]

+1 vacuum leaks. They can cause all sorts of mischief. Do you have any pending codes or is the CEL on?

Originally Posted by Anker

And also check for vacuum leaks. They typically have the greatest effect when idling.

[jcslocum]

Is this happening when you are pushing down on the brake pedal?

[pidj]

No CEL (have not checked if there are 'hidden' codes - sorry I don't know the term used when there is a code in the history but no light on the dash). I thought maybe the idle is affected when I depress the clutch, but I never considered the brake involvement. I'll check the connections (as the throttle body was cleaned in Feb) and clean the MAF to see if that changes anything.

[jcslocum]

If you have a vacuum leak in the booster/servo it may be leaning out the idle enough to cause the idle drop.

[jim_hoyland]

I just experienced almost the same problem and mu local Indy shop is a little baffled.
When I start up the motor, idle ranges from 1,000 to 500; back and forth. After taking to local shop, mechanic found the rough idle goes away after disconecting the MAF. No codes. A second and third MAF were installed with no change.
The suspected gremlin is a vacuum leak; but I need some clues as to where to look

Any tips/ suggestions will bee greatly appreciated...

[rexcramer]

Find a mechanic with a smoke generator.

[M31]

I had the exact same issue on my '02 S last week. Idle would go up to 1500 then down to 800 on it's own without my foot on the gas. My local garage pulled code P0507 on the diagnostic (idle control at stop) so they removed and cleaned throttle body. All was well for about 24 hours and then all hell broke loose! While waiting at a red light idle starting racing again and white smoke began billowing out the tailpipe like a giant refer from a Cheech & Chong movie! Turned out to be the infamous air/oil separator that I've been reading about on this forum. Returned to garage and mechanic found 15" of vacuum at the dipstick when there should be no more than .25" at any time according to him. Replaced the air/oil separator, cleaned the throttle body again which allowed it to idle around 700-800 consistently. It's been a week and no further issues so I suspect it was the air/oil separator from the start which prevented the throttle body to close in the first place. :ah:

[cas951]

Originally Posted by oldskool73

Maybe also try cleaning the throttle body?

https://www.youtube.com/watch?v=slPzoplzWT0

My car was doing exactly that. I cleaned the MAF and throttle body and this resolved the issue.

[jim_hoyland]

Thanks for the tips; I made a short list and showed them to my local Indy
I’ll post the results when he completes the repair.

[jim_hoyland]

Local Indy found an InterceptLink Air Flow Meter Correction module wired to the CPU
See pic
Also replaced Oil seperator and air filter; runs like new car !
I’ll upload a pic later...
My HC results in smog tests have been near the cut off limit the past 4 times the car was smogged; wondering if this device caused that too ?