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Old 03-09-2012, 08:59 AM   #1
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"Bouncing" RPM's

Hi Guys. Just got my first Porsche yesterday, a '98 Boxster base. I've noticed that when coming off of the gas (say coming to a stop), the RPM's will drop WAY low, like 500, then bounce up to 1200 then drop to 700, then up to a 1000, etc until it settles in at about 850 RPM. It died on me today on the first "bounce". Any ideas? Thanks!

Brad

Last edited by zapna; 03-23-2012 at 05:20 PM.
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Old 03-09-2012, 11:26 AM   #2
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e-throttle ?
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Old 03-09-2012, 11:46 AM   #3
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Not e-gas from the year. Now how about CELs or Codes?
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Old 03-09-2012, 12:33 PM   #4
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Try cleaning the idle control valve, and of cousre, the throttle body while you are already there.
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Old 03-09-2012, 12:37 PM   #5
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Here is your solution...

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Originally Posted by zapna View Post
Hi Guys. Just got my first Porsche yesterday, a '98 Boxster base. I've noticed that when coming off of the gas (say coming to a stop), the RPM's will drop WAY low, like 500, then bounce up to 1200 then drop to 700, then up to a 1000, etc until it settles in at about 850 RPM. I died on me today on the first "bounce". Any ideas? Thanks!

Brad
... cleaning the idle control valve, as was recommended above.
Instructions here: Clean the Throttle Body

Happy Boxstering,
Pedro
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Old 03-09-2012, 02:14 PM   #6
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Thanks everyone. I am waiting for my Bentleys manual to arrive (just in case) then I will give it a shot and let you know the results.
Brad
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Old 03-09-2012, 07:45 PM   #7
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You will find more useful information at Pedro's website then the bentley book (which is nice to have too)
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Old 03-10-2012, 01:19 AM   #8
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Pedro's site looks great, lots of very useful info! And lots of projects I am definitely going to tackle. But I dont even know how to put the top in the service position, so the Bentley's is a must. It is my bible on my aircooled VW.
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Old 03-10-2012, 02:28 AM   #9
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service position = "partially opened" so that the Z is up and the top is about half-way back. then disconnect the rods holding the back (with the plastic window) and push it forward so it's folded away.

easy-peasy

from another thread:

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Old 03-10-2012, 03:42 AM   #10
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Is there a bouncing rpm virus going around? I hope you didnt catch it from me!

Anyway, start with the codes. If you dont have the reader go to a auto part store and have them tell you the codes. Then on to the surgeries. The bently manual is good. Should get one. But, the help here and Mike and Pedros website are very useful.
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Old 03-11-2012, 06:56 AM   #11
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You guys seem much more laid back than the VW guys over on the Samba. They will rip you one if you ask a question that is answered in Bentley's. Once bitten, twice shy.

I love Pedro's site! Some great write-ups on cool mods that I plan on.

I did my first mod yesterday, my car is now de-snorkeled! Sounds great.

I didn't realize a standard code reader would read Porsche codes. I thought you had to use a PSWIS, PST2, or hammer. I will definitely invest in one of those! Any suggestions on the most bang for the buck?

I should also mention that the car didn't do it all day yesterday during a PCA event, but when I took it to dinner, it did it again, so it seems to come and go.

Thanks Gents!
Brad
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Old 03-11-2012, 11:44 AM   #12
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Diagnostic Tool for Porsche | Durametric
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Old 03-11-2012, 12:29 PM   #13
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+1 on Durametric.

Comes with 3 vin license. Can upgrade to unlimited by paying the difference later. Does all that I need to without letting me crash the computer.
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Old 03-11-2012, 02:40 PM   #14
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I didn't realize a standard code reader would read Porsche codes. I thought you had to use a PSWIS, PST2, or hammer.
a standard reader will deal with mostly emissions stuff. the durametric will delve deeper into the computer(s). get one, it's well worth the investment. save $200 on a regular reader and only see 15% of what's going on with the car.

Comparing Durametric Porsche Diagnostic Software to OBD2 (OBDII) Diagnostic tools.
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Old 03-12-2012, 08:29 AM   #15
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Its ordered!

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Old 03-22-2012, 06:21 PM   #16
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So, I got my Durametric and checked my codes today and I have no engine faults. (Yay!) Only code 21 for the airbag, even though the airbag light isn't on. I also got the top in the service postion and rooted around the engine compartment, familiarizing myself with everything. I also read a bunch of sections in my Bentleys and am getting much more confident with the engine layout. I am going to try driving with the Duramentric hooked up and see if I can get the RPM "bounce" on the graph, but its been happening much less frequently lately. Any other parameters I should be running at the same time?

Thanks!
Brad
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Old 03-22-2012, 06:25 PM   #17
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The no error code screen and the airbag error code:

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Old 03-22-2012, 08:55 PM   #18
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Hey, I got bit by the hunting idle today too. Figured it was the idle control valve. Always good to hear some consensus/confirmation.
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Old 03-25-2012, 04:42 AM   #19
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So, I ran an "actual values" graph for RPM and ignition timing at idle and this is what I got. Is this normal?

I would think the timing should be rock solid.

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Old 03-25-2012, 04:05 PM   #20
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Here is how my last few days went:

After the hunting idle started, the next day I had big billows of smoke occasionally come out the exhaust so I replaced the AOS. Car ran great and idle was back to rock steady. Thought all was fine.

Then the next day, the car died once when idling and would not re-start - crank over, almost catch and then die. Disconnected MAF and the engine started up fine. Replaced MAF and now back to normal, idle rock steady.
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