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Old 07-04-2014, 01:12 PM   #1
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Mystery Problem, Limited RPMs

Hey Peeps,
This is my first post on here. Let's see if I can make it count.

2000 Boxster, 54k miles. It's had the rough idle thing since I bought the car. once it gets warm, the idle floats up and down from 500-800 rpms or so but only at an idle. Everything else runs great. BUT...

Today I got it home, turned off the car, ran inside, came out, and the car wouldn't start. crank like crazy but it was like there was no spark or fuel (crank sensor....) I put the gas to the floor and it starts. I take it to the gas station. fill up on 93 octane. turn the car off, wont start again. several minutes later, she starts. (crank sensor....) I drive it home, park it where I am ready to put it up on jack stands. Shut it off, same thing, hard to get restarted BUT, this time... omg.. this time, the idle is at about 1k, and i can put the gas pedal to the floor and the revs slowly come up to 1400-1500 rpm and then fall back down to 1100 rpm. the revs come on and go off slow.

No codes being thrown...

I am thinking fuel pump. My mechanic thinks maybe its related to the air oil seperator and its some kind of vapor lock.

Internet Porsche gods! Heed my call! What the hell is going on here!?

- Patrick
Syracuse, NY


*** Problem solved 2 weeks later ***
Spoiler Alert

Car threw Code P1502 which is "Throttle Jacking Unit Spring Test" so I took the throttle body apart and cleaned it real good and reassembled. Reset the EGAS pedal "Thing" by turning the key to on for 1 minute, back to off for 10 seconds then starting the car, problem persisted, so I then used the code reader to clear the code, car fired right up. I spent a lot of money on parts and tools I didn't need but I learned a lot. Worth every penny. Enjoy this thread.


Last edited by virgosunleomoon; 07-20-2014 at 01:53 AM.
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Old 07-04-2014, 05:11 PM   #2
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What did you use to check for codes? Have you checked the fuel pressure? With nothing touching the gas pedal and the car off, turn the key to the run position (not cranking) for 90 seconds, turn off for at least 20 seconds, then start the car. This baselines the gas pedal idle position to the DME.
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Old 07-04-2014, 05:22 PM   #3
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turned key to on for 90 seconds, then back to off for 20 seconds then started the car. Started with a small hesitation/shake and then took an idle of 1000. stepping on the gas brought the RPM up to 1100. no higher.

The Engine light has not come on, no codes.
What does DME stand for?
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Old 07-04-2014, 05:30 PM   #4
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DME is the engine computer.

You need to have the codes read, codes can exist without lighting the check engine light.

Check fuel pressure.
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1987 924S. 2002 996TT. PST2
Owned and repaired Porsches since 1974. Have driven them all the way the Dr intended...
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Old 07-04-2014, 06:01 PM   #5
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ok, the engine computer is called the DME. I will buy a code reader tomorrow at Harbor Freight. I hear you can get a good one for about $70. I didn't know it could throw codes without turning on the Check Engine Light hense the CEL...

What is the easiest way to check fuel pressure?

(I have never seen a problem where standing on the gas pedal on a running car doesn't result in a redlined engine.)
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Old 07-04-2014, 06:05 PM   #6
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The gas pedal is electronic and is connected to the DME with 6 wires.

Autozone has been known to lend fuel pressure testers and to read codes.
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1998 Boxster with 7.8 DME, 2005 3.6 liter/325 hp, Variocam Plus, 996 Instrument panel
2001 Boxster bought new. Installed used motor at 89k.
1987 924S. 2002 996TT. PST2
Owned and repaired Porsches since 1974. Have driven them all the way the Dr intended...
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Old 07-04-2014, 06:05 PM   #7
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Forgive my ignorance, but is a 2000 base e-gas or cable controlled?

I ask because I went through something similar with mine and it turned out to be that the cable was hung up on top of the throttle body (iirc).
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Old 07-04-2014, 06:09 PM   #8
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If it's a 2.7, it's egas.

Here's some related threads:

My Boxster is acting like an idiot

How to diagnose and resolve engine issues using Durametric.
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1998 Boxster with 7.8 DME, 2005 3.6 liter/325 hp, Variocam Plus, 996 Instrument panel
2001 Boxster bought new. Installed used motor at 89k.
1987 924S. 2002 996TT. PST2
Owned and repaired Porsches since 1974. Have driven them all the way the Dr intended...

Last edited by Paul; 07-04-2014 at 06:33 PM.
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Old 07-04-2014, 06:26 PM   #9
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Quote:
Originally Posted by Paul View Post
The gas pedal is electronic and is connected to the DME with 6 wires.

Autozone has been known to lend fuel pressure testers and to read codes.
Second the Autozone comment. I've seen Autozone employees UNDER CARS in the parking lot helping customers. They would probably check the codes for you.
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Old 07-04-2014, 07:35 PM   #10
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ok, well the car cant be driven down the street so I will just get the code reading device and try to borrow the fuel pressure tool. I am going to retighten/replace the AOS which was proving to be difficult to get out and return the car to engine running ability.

I will look for codes and test fuel pressure.

Thanks for some direction.

- Patrick
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Old 07-04-2014, 08:01 PM   #11
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have tried cleaning the throttle body? this is a simple task that i would try first before wasting too much money. the symptoms are exactly what you are describing. at idle, the engine wants to just shut off.
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Old 07-04-2014, 08:44 PM   #12
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egas pedal video:

https://www.youtube.com/watch?v=vB0Sd7rRW-c
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1998 Boxster with 7.8 DME, 2005 3.6 liter/325 hp, Variocam Plus, 996 Instrument panel
2001 Boxster bought new. Installed used motor at 89k.
1987 924S. 2002 996TT. PST2
Owned and repaired Porsches since 1974. Have driven them all the way the Dr intended...
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Old 07-05-2014, 06:04 AM   #13
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Quote:
Originally Posted by tuanle16 View Post
have tried cleaning the throttle body? this is a simple task that i would try first before wasting too much money. the systems are exactly what you are describing. at idle, the engine wants to just shut off.
I don't see how a dirty throttle body would catastrophically(sp) stop my car from revving and make it not start. The rough idle maybe but I can't get the car over 1100 rpms.
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Old 07-05-2014, 06:07 AM   #14
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Quote:
Originally Posted by Paul View Post
Looks like a great video, I will watch it later.

Just picked up a code reader and vacuum gauge. System has no codes active and I will test the fuel pressure later today.
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Old 07-05-2014, 06:08 AM   #15
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Could also be a problem with the evap system.

Success! Finally fixed the hard start while hot and fueling issues.
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Old 07-05-2014, 06:58 AM   #16
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reconnected the AOS, started up the car. hovered at about 1000 RPM. started pinching hoses on top of the engine, at random. no change. gas pedal does nothing. then, before my very eyes... the CEL comes on. shut off car, plugged in code reader and...

P1502 - Fuel Pump Relay
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Old 07-05-2014, 11:32 AM   #17
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grabbed a fuel pump relay from a 1999 996 (same part) and the car is doing the exact same thing. Car starts (a little rough) and stays at 1000 RPMs and applying the gas pedal only gets you up to 1100 RPMs and it comes back down to 1075 RPM and stays there.

I ordered Porsche specialty tool 9559 so I can check the fuel pressure. My cheap Harbor freight fuel pump gauge and adapters don't fit on this schrader valve.
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Old 07-05-2014, 12:27 PM   #18
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Sounds like your drive-by-wire is not working properly. If you look above the gas pedal under the dash you will see the actual "sensor" that tells the DME how much throttle is required by the driver. I have read online about people disassembling this part to clean it & make it function again. You might try vacuming it 1st before disassembly. Search internet for more info. I've never done this personally.
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Old 07-05-2014, 03:13 PM   #19
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This is one of the codes that can be caused by a faulty gas pedal sensor or bad wiring from the sensor to the DME:



Notice the rpm:



When you get this, gas pedal does nothing, Note: this does not light the check engine light:



None of these faults lit the engine check light:

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1998 Boxster with 7.8 DME, 2005 3.6 liter/325 hp, Variocam Plus, 996 Instrument panel
2001 Boxster bought new. Installed used motor at 89k.
1987 924S. 2002 996TT. PST2
Owned and repaired Porsches since 1974. Have driven them all the way the Dr intended...

Last edited by Paul; 07-05-2014 at 03:20 PM.
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Old 07-05-2014, 03:17 PM   #20
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Since you were working on the AOS, any chance you loosened or damaged the connector or wiring for the throttle motor?

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1998 Boxster with 7.8 DME, 2005 3.6 liter/325 hp, Variocam Plus, 996 Instrument panel
2001 Boxster bought new. Installed used motor at 89k.
1987 924S. 2002 996TT. PST2
Owned and repaired Porsches since 1974. Have driven them all the way the Dr intended...
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