Results 1 to 19 of 19
  1. #1
    nizmo's Avatar
    nizmo is offline PCA Member
    Join Date
    Jul 2007
    Location
    CA
    Posts
    32
    Downloads
    7
    Uploads
    0

    rpm varies at idle

    I did a search but couldn't find anything specific to this topic. I've noticed that my rpm varies a little bit when I'm idling at a stoplight, even after the car has been driven around for a long time. Its not a large variation, but if I look at the rpm gauge, I can notice that the gauge moves slightly up and down. Is this normal?


  2. #2
    proy is offline Porsche Person
    Join Date
    Oct 2006
    Posts
    7
    Downloads
    2
    Uploads
    0
    mine does this also. probably moves up to 100rpm on bad days. took it in and whilst porsche acknowledged not normal, they ran full diagnostics and held car overnight to check again and they concluded unusual tacho movement but totally normal operations of engine. Also interesting test is to set your car on cruise control on flat road at say 3000rpm and I notice my tacho needle still moves around a bit at constant MPH. I am not stressed about it though, I have pointed it out to dealer and if it ever causes problems in future I am sure they will look after me given problem identified early on.

    Cheers

  3. #3
    beach987's Avatar
    beach987 is offline Boxster Enthusiast
    Join Date
    Sep 2008
    Location
    Florida
    Posts
    76
    Downloads
    71
    Uploads
    1

    RPM Fluctuation at Idle- Porsche Premier Dealer Mechanic Stumped

    My 2005 2.7 (25k miles) Boxster has been in the shop now for 3 weeks. The dealer is at a loss as to why, while at idle, the rpm's bounce up and down between 300 and 800. There are no fault codes. It only does it after the car has warmed up and is at idle.

    They have consulted Porsche and thus have reprogrammed the DME, replaced the ECU, replaced sensors (not sure which), replaced the A/C compressor and now are going to replace the throttle body. They have admitted they really have no clue as to why it is doing this and are just replacing parts in hopes of stumbling upon a fix. Fortunately they are covering it under warranty and are adamant that they will not return the car to me until they track down and repair what is wrong. Looks like I may miss Zone 12 Zonefest next week.

    Does anyone here have any ideas that I can pass onto the mechanic? Is my 2.7 987 the only one that has ever had this issue? There are some pretty knowledgeable tuner/modders around these boards that seem to know a lot about these engines and systems. Do any of you have any ideas?

    Thanks in advance for the help.

    P.S. Is it reasonable or usual for a mechanic to remove the replaced items like the ECU and A/C compressor once they have determined these not to be the issue?

  4. #4
    4by4's Avatar
    4by4 is offline Crusin worlds most isolated city
    3,000 post club
    Join Date
    May 2006
    Location
    down-under
    Posts
    3,589
    Images
    37
    Downloads
    40
    Uploads
    2
    Blog Entries
    8

    Re: RPM Fluctuation at Idle- Porsche Premier Dealer Mechanic Stumped

    All the Caymans do it to a very small degree and usually if you press the gas very slightly it does it more. Press it more again and it disappears.
    However yours sounds rather extreme.
    Was it ok previously?

    My bet in on the TB and in conjunction with ECU control software (not ECU hardware). I'm pretty sure the control loop software algorithm design has a resonate mode exasperating the issue.
    Also check the idle RPM and for any air leaks as well.
    2010 Cayman S, special build.

  5. #5
    CJP80's Avatar
    CJP80 is offline Porsche Enthusiast
    Join Date
    Jun 2008
    Location
    UK
    Posts
    243
    Images
    3
    Downloads
    51
    Uploads
    1

    Re: RPM Fluctuation at Idle- Porsche Premier Dealer Mechanic Stumped

    This sometimes happens to me if I nudge the gas pedal very lightly and quickly lift off. Could the sensor in the pedal be sending out spurious signals?

    Also, when my PS pump went, this was a symptom...have them look at that also.

    Cheers

    Chris
    981C GTS - Rhodium Silver, Satin Platinum Wheels, PTV, PDK, Light Design package

  6. #6
    intubator's Avatar
    intubator is offline Porsche Specialist
    500 post club
    Join Date
    Aug 2007
    Location
    MD
    Posts
    662
    Downloads
    38
    Uploads
    0
    My Classifieds

    Re: RPM Fluctuation at Idle- Porsche Premier Dealer Mechanic Stumped

    You mention they replaced sensors, does that include the MAF sensor? My car does this very thing with and usually without throwing codes when the MAF is oily, a common issue with the intake system in our cars. A simple cleaning with MAF solvent does the job. If this is the problem then you will find that the entire intake housing up to the throttle body will be oily and should be cleaned as well. Good luck!! By the way I have had to clean my MAF several times, I have about 30,000 miles on my car and usually keep the oil about a half quart under the top mark.

  7. #7
    4by4's Avatar
    4by4 is offline Crusin worlds most isolated city
    3,000 post club
    Join Date
    May 2006
    Location
    down-under
    Posts
    3,589
    Images
    37
    Downloads
    40
    Uploads
    2
    Blog Entries
    8

    Re: RPM Fluctuation at Idle- Porsche Premier Dealer Mechanic Stumped

    MAF, yes good one.
    We can thank the oil ingestion issue for that.
    2010 Cayman S, special build.

  8. #8
    beach987's Avatar
    beach987 is offline Boxster Enthusiast
    Join Date
    Sep 2008
    Location
    Florida
    Posts
    76
    Downloads
    71
    Uploads
    1

    Re: RPM Fluctuation at Idle- Porsche Premier Dealer Mechanic Stumped

    I finally got my Boxster back. The dealer indicates that the A/C compressor they installed was faulty. They installed another new compressor and that solved the problem. I have had the car back for two days now and it is running flawlessly.

    Thank you all for your suggestions and help. I really appreciate it.

    Miles

  9. #9
    beez's Avatar
    beez is offline Site Donor
    6,000 post club
    Join Date
    Dec 2005
    Location
    Las Vegas, Nevada
    Posts
    6,825
    Images
    13
    Downloads
    55
    Uploads
    3

    Re: RPM Fluctuation at Idle- Porsche Premier Dealer Mechanic Stumped

    Quote Originally Posted by beach987 View Post
    I finally got my Boxster back. The dealer indicates that the A/C compressor they installed was faulty. They installed another new compressor and that solved the problem. I have had the car back for two days now and it is running flawlessly.

    Thank you all for your suggestions and help. I really appreciate it.

    Miles
    Great news, Miles. Always good to hear a success story from the service department...

    brad
    22-year PCA Member
    PCA DE Instructor

  10. #10
    4by4's Avatar
    4by4 is offline Crusin worlds most isolated city
    3,000 post club
    Join Date
    May 2006
    Location
    down-under
    Posts
    3,589
    Images
    37
    Downloads
    40
    Uploads
    2
    Blog Entries
    8

    Re: RPM Fluctuation at Idle- Porsche Premier Dealer Mechanic Stumped

    Quote Originally Posted by beach987 View Post
    I finally got my Boxster back. The dealer indicates that the A/C compressor they installed was faulty. They installed another new compressor and that solved the problem. I have had the car back for two days now and it is running flawlessly.

    Thank you all for your suggestions and help. I really appreciate it.

    Miles
    Great, a nice simple problem.
    2010 Cayman S, special build.

  11. #11
    CJP80's Avatar
    CJP80 is offline Porsche Enthusiast
    Join Date
    Jun 2008
    Location
    UK
    Posts
    243
    Images
    3
    Downloads
    51
    Uploads
    1

    Rev Needle - Idle Wobble

    So my rev needle has started to wobble at idle, not significantly but enough for me to notice the change in engine note.

    I got out my trusty Durametrics cable and measured the roughness on each cylinder. No. 2 seems to vary by a a greater degree at idle, +/-2.5% vs +/- 1% for each of the others. Things normalise when I rev the engine above 1Krpm.

    Is this normal or do I have a dodgy plug/coil pack?

    Can anyone advise where No.2 actually is?

    Thanks folks,

    Chris
    981C GTS - Rhodium Silver, Satin Platinum Wheels, PTV, PDK, Light Design package

  12. #12
    beez's Avatar
    beez is offline Site Donor
    6,000 post club
    Join Date
    Dec 2005
    Location
    Las Vegas, Nevada
    Posts
    6,825
    Images
    13
    Downloads
    55
    Uploads
    3

    Re: Rev Needle - Idle Wobble

    Three threads - same topic - merged.

    brad
    22-year PCA Member
    PCA DE Instructor

  13. #13
    Tomasz's Avatar
    Tomasz is offline Porsche Orator
    1,000 post club
    Join Date
    May 2007
    Location
    WA
    Posts
    1,739
    Images
    42
    Downloads
    40
    Uploads
    0

    Re: RPM Fluctuation at Idle- Porsche Premier Dealer Mechanic Stumped

    Mine went away after refueling with Shell.
    Tomasz

    Apologies for spelling mistakes, most of them are keyboarding errors. To enjoy this forum I run out of time to proof read.

  14. #14
    lbk8950 is offline Porsche Prophet
    Join Date
    Jan 2011
    Location
    Michigan
    Posts
    66
    Downloads
    5
    Uploads
    0

    Re: RPM Fluctuation at Idle- Porsche Premier Dealer Mechanic Stumped

    Digging up an old thread. I am having the same fluctuating idle problem. My car is under warranty (CPO) and I am considering taking it to the dealer.
    Last edited by lbk8950; 03-22-2011 at 06:56 AM.

  15. #15
    waterbeetle's Avatar
    waterbeetle is offline Porsche Chatter
    Join Date
    Feb 2011
    Location
    Boston, MA
    Posts
    18
    Downloads
    0
    Uploads
    0

    Re: Rev Needle - Idle Wobble

    Quote Originally Posted by CJP80 View Post
    So my rev needle has started to wobble at idle, not significantly but enough for me to notice the change in engine note.

    I got out my trusty Durametrics cable and measured the roughness on each cylinder. No. 2 seems to vary by a a greater degree at idle, +/-2.5% vs +/- 1% for each of the others. Things normalise when I rev the engine above 1Krpm.

    Is this normal or do I have a dodgy plug/coil pack?

    Can anyone advise where No.2 actually is?

    Thanks folks,

    Chris
    #2 is the middle cylinder, passenger side

  16. #16
    Rockster is offline Porsche Idealist 500 post club
    Join Date
    Apr 2009
    Location
    Livermore, CA
    Posts
    799
    Downloads
    2
    Uploads
    0

    Re: RPM Fluctuation at Idle- Porsche Premier Dealer Mechanic Stumped

    Take it in. That is what CPO warranty is for. IIRC idle speed is 740 rpms +/- 40 rpms. This is the factory manual call out.

    If the idle is higher or lower than this and varies by more than this something is wrong.

    Sincerely,

    Rockster.

  17. #17
    DocSteve's Avatar
    DocSteve is offline Porsche Enthusiast
    Join Date
    Mar 2011
    Location
    Grants Pass, OR
    Posts
    186
    Images
    3
    Downloads
    1
    Uploads
    0

    Re: rpm varies at idle

    Maybe off base but after 9K I installed a IPD plenum while doing the change I noticed a lot of carbon built up on the throttle body butterfly. You might want to clean yours It's pretty easy to get at the stock hose between the Mass air flow and throttle body off and spray some carb cleaner in that area. Do not use this type of cleaner on the mass air flow meter closer to the air filter - would be very bad!! Gentley open the butterfly with your finger and spray in a short burst, use a lintless cloth and wipe out debris. Let stand for 10 min to allow cleaner to evaporate off. See if this fixes your trouble..

  18. #18
    EvoRoadster's Avatar
    EvoRoadster is offline Site Donor
    500 post club
    Join Date
    Dec 2010
    Location
    Oahu, Hawaii
    Posts
    500
    Downloads
    0
    Uploads
    0

    Re: rpm varies at idle

    Quote Originally Posted by DocSteve View Post
    Maybe off base but after 9K I installed a IPD plenum while doing the change I noticed a lot of carbon built up on the throttle body butterfly. You might want to clean yours It's pretty easy to get at the stock hose between the Mass air flow and throttle body off and spray some carb cleaner in that area. Do not use this type of cleaner on the mass air flow meter closer to the air filter - would be very bad!! Gentley open the butterfly with your finger and spray in a short burst, use a lintless cloth and wipe out debris. Let stand for 10 min to allow cleaner to evaporate off. See if this fixes your trouble..
    I will go one step further and say: DO NOT USE CARB CLEANER, USE THROTTLE BODY CLEANER. I feel better now.
    2012 Peridot Cayman R
    2013 Honda Ridgeline RTL
    2012 BMW 328iT Sport Wagon

  19. #19
    sc3003 is offline Newbie
    Join Date
    Nov 2014
    Location
    California
    Posts
    1
    Downloads
    0
    Uploads
    0

    Re: RPM Fluctuation at Idle- Porsche Premier Dealer Mechanic Stumped

    Hi Miles, Hope you're still out there as I'm having this same problem with my 2005. I also have a/c issues so I'm thinking the compressor may be my problem too.
    Did your car only do the idling issue when the A/C was running or did it do it anytime?
    Cheers and thank you!
    Spencer

    Quote Originally Posted by beach987 View Post
    I finally got my Boxster back. The dealer indicates that the A/C compressor they installed was faulty. They installed another new compressor and that solved the problem. I have had the car back for two days now and it is running flawlessly.

    Thank you all for your suggestions and help. I really appreciate it.

    Miles

Similar Threads

  1. rpm varies at idle
    By nizmo in forum 987 Cayman and Boxster Chat
    Replies: 0
    Last Post: 09-20-2007, 10:06 AM
  2. AC Temp Fluctuation at low RPM?
    By Kman-Went in forum 987 Cayman and Boxster Problems and Complaints
    Replies: 7
    Last Post: 08-02-2006, 05:29 PM
  3. What is your RPM at idle? Mine is 700 rpms
    By RussK in forum 987 Cayman and Boxster Chat
    Replies: 5
    Last Post: 05-29-2006, 07:14 PM
  4. Buy this at your Porsche Dealer!
    By Crazy_fast in forum Video Games
    Replies: 0
    Last Post: 11-17-2005, 07:37 PM
  5. Buy this at your Porsche Dealer!
    By Crazy_fast in forum 987 Cayman and Boxster Chat
    Replies: 0
    Last Post: 11-17-2005, 07:37 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •