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.

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.

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?

DME is the engine computer.

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

Check fuel pressure.

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.)

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.

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).

If it's a 2.7, it's egas.

Here's some related threads:

http://986forum.com/forums/performance-technical-chat/52971-my-boxster-acting-like-idiot.html

http://986forum.com/forums/performance-technical-chat/52071-how-diagnose-resolve-engine-issues-using-durametric.html

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.

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

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.

egas pedal video:

https://www.youtube.com/watch?v=vB0Sd7rRW-c

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.

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.

Could also be a problem with the evap system.

http://986forum.com/forums/performance-technical-chat/50264-success-finally-fixed-hard-start-while-hot-fueling-issues.html

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

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.

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.

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:

http://i33.photobucket.com/albums/d6...6/P5230718.jpg

Notice the rpm:

http://i33.photobucket.com/albums/d6...6/P5230719.jpg

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

http://i33.photobucket.com/albums/d6...6/P5230720.jpg

None of these faults lit the engine check light:

http://i33.photobucket.com/albums/d6...6/P5230721.jpg

Since you were working on the AOS, any chance you loosened or damaged the connector or wiring for the throttle motor?

ok, I didn't start messing with the AOS until after the problems started. If I was the pedal sensor, that wouldnt explain the rough start. It only had one fault code and its the one I posted earlier.

I am just waiting on one more speciality tool to arrive and I am going to...
1. Replace the fuel pump and sending unit (snapped the top off the old sending unit)
2. Re-install battery and attempt start. If it fails.
3. Take fuel pressure at fuel rail. (I have the tool now.)
4. Replace fuel filter and try again. (I have a new one.)
5. Peplace fuel pump relay and try again. (I have a new one)
6. Check pedal sensor and try again.
7. Return to drawing board.

Don't give up on me guys, I enjoy the feedback and ideas.

Keep in mind that there are 2 potentiometers for the e-gas for redundancy. When 1 fails, RPMs are limited by the ECU exactly as you describe.
Sorry if it's been said before.

ok, where are those 2 "potentiometers"?

I replaced the fuel pump and sending unit.
I replaced the fuel filter.
I have a new fuel pump relay that didn't make a change.

My throttle body is apart in my hands right now, will put it back together clean and see what happens. not too much oil in there, seems to be ok. i will post later.

PS - the fancy fuel pressure hose I bought from the dealership, it has a metric end and I cant screw it onto the gauge I have. -grrr-

and Paul, good point on the connection for the throttle body, I will make sure its tight when it goes back in.

PS - AND WE STILL HAVE P1502 for a CEL.... (Throttle Body not put back together yet...)

PROBLEM SOLVED - In the end, it was the P1502 code that was the problem and the cure. My new Can-Tech OBD II tool showed the P1502 code and below it it said "Fuel Pump Relay End Limit. Porsche Part $11" Seeing this I assumed it was a Fuel Pump Relay code. After changing the fuel pump/sending unit/fuel filter and trying out my new fuel pump relay, I was discouraged so I texted my buddy who is the head mechanic at the Porsche dealership (yeah, tried to do it without him) and he said 1502 was a throttle body error code. Not happy hearing this, I opened my Bentley Service Manual and looked it up.

P1502 - Throttle Jacking Unit Spring Test

I almost crapped my pants. Why the hell did the OBD reader say "Fuel Pump Relay?" I couldn't believe it. I took the TB apart, cleaned it real good, exercised it, put it all back together, and started it up. Very rough idle but I could get it to 2300rpms!! On the right track I said! So I did the EGAS remapping thing where you turn the key to on for a minute and then off for ten seconds and start it. same thing. Then I cleared the code with the OBD reader and started it up.

OMG, it was like a new car. Not only did I have my revs back but after the car got to temperature, there was no flutter in the idle. I was so happy, I took it out and set a personal record for fastest speed on four wheels. 145mph

The throttle body wasn't really THAT dirty so I think I am just going to order a new one and throw it in there so I don't have any issues in the future.

I want to thank everyone who contributed to the effort in getting my baby back to normal. Got 3 days at Watkins Glen August 22nd, 23rd, and 24th. I was starting to sweat a little. -wink-