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Old 07-18-2021, 11:03 AM   #1
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Car Dies

Please I need help. My Car has been idling poorly .backfires thru intake occasionally when accelerating runs rough to about 1500 rpm then smooths out .When coming to a stop rpm goes below 300 and sometimes the car dies before rpm stabilizes at Normal idle speed . It will fire right back up and has no codes . I took the car to the Porsche Dealership , they had the the car for 4 weeks .After two weeks they said they don't see any vacuum leaks no codes and they do not know what's wrong ? Suggested replacing mas air flow sensor. They said they were pretty sure that's the problem. They replaced the sensor and said its better but not right .This cost 900.00 . They said to make it right I need to replace my coils and injectors to get the car running right cost 2200.00 more. I said I will come get the car . The coils in the car were 6 months old .I guess at this point I have no choice but to change injectors myself .6 months ago I had to have a cracked heads replaced and it has not run right sine then .I pulled the engine myself and sent the heads to Hoffmans machine. Is it possible My trimming is a off 1 degree or so and causing these problems .? Or do you have any idea whats my problem ? Thank you all.

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Old 07-18-2021, 11:22 AM   #2
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Please I need help. My Car has been idling poorly .backfires thru intake occasionally when accelerating runs rough to about 1500 rpm then smooths out .When coming to a stop rpm goes below 300 and sometimes the car dies before rpm stabilizes at Normal idle speed . It will fire right back up and has no codes . I took the car to the Porsche Dealership , they had the the car for 4 weeks .After two weeks they said they don't see any vacuum leaks no codes and they do not know what's wrong ? Suggested replacing mas air flow sensor. They said they were pretty sure that's the problem. They replaced the sensor and said its better but not right .This cost 900.00 . They said to make it right I need to replace my coils and injectors to get the car running right cost 2200.00 more. I said I will come get the car . The coils in the car were 6 months old .I guess at this point I have no choice but to change injectors myself .6 months ago I had to have a cracked heads replaced and it has not run right sine then .I pulled the engine myself and sent the heads to Hoffmans machine. Is it possible My trimming is a off 1 degree or so and causing these problems .? Or do you have any idea whats my problem ? Thank you all.
So I need basic information to start:
Year of car.
Mileage
any modifications including air filter.
Any idea what caused the original heads to crack??
Did both heads crack.???

all work done trying to fix the issue.
Any CEL or codes in the past??

Get your hands on a standard vacuum test gauge and do a vacuum test at the intake, with the car fully warmed up and at idle. Record the reading and the action of the needle if any. Such as steady needle, needle drifting between two readings, needle ticking.

When sitting in neutral engine fully warmed up what is the idle RPM?
What is the idle like??? steady? hunting? up and down?????

If idle is rough hold RPM at 1500-2500 does the engine smooth out??

The more info you can give me the better chance I have of helping you.
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Old 07-18-2021, 11:47 AM   #3
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Pay attention to Blue here, he knows what he is asking.
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Old 07-18-2021, 11:48 AM   #4
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Car is a 2000 Boxster S , had an RDN 3.2 engine put in 40k miles ago 10 k ago Bank one head developed a crack and dumped oil into coolant .Heads were pulled sent to a Porsche head specialist who preformed a pressure test .Repaired head checked vale springs did a valve job. I put the ending together .All new Porsche gaskets , ARP head studs. The engine has not run correctly since then . I took it to a shop around the corner and they said I had multiple misfires . I replaced all the coils twice the plugs mass air flow sensor, air filter (stock) , O2 sensors . Car has no codes .
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Old 07-18-2021, 11:54 AM   #5
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When you had it at the dealer, did they check timing? Having going through something somewhat similar with misfires, timing is important.

When you did the head, did you replace the cam actuator and/or pads?
Which plugs & coils are you using?
What are you using to read the codes? Some readers wont pull pending codes, only set codes.

Just curious, what are you doing to the car to need a replacement engine and then that replacement crack it's head?
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Old 07-18-2021, 11:57 AM   #6
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Just saw one of your previous posts. I think this car is haunted. 4 motors in 20 years?
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Old 07-18-2021, 12:08 PM   #7
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Car is a 2000 Boxster S , had an RDN 3.2 engine put in 40k miles ago 10 k ago Bank one head developed a crack and dumped oil into coolant .Heads were pulled sent to a Porsche head specialist who preformed a pressure test .Repaired head checked vale springs did a valve job. I put the ending together .All new Porsche gaskets , ARP head studs. The engine has not run correctly since then . I took it to a shop around the corner and they said I had multiple misfires . I replaced all the coils twice the plugs mass air flow sensor, air filter (stock) , O2 sensors . Car has no codes .
Interesting that they say there were multiple misfires yet it shows no codes.
Misfires are usually set on the first occurrence.

So what RPM does the car idle at when fully warmed up and in neutral??
What is the idle like???? smooth??? lumpy??? hunting??? raising and falling???

If the idle is anything other then smooth does the engine smooth out if you hold the RPM at 1500-2500RPM???
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Old 07-18-2021, 12:56 PM   #8
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I have durametrics software .When I got the car it had a Porsche replacement, the original had an ims issue . This motor had low oil pressure when I got it so I replaced it . Car idle is normal at 700 rpm . The tac dose not hunt , rpm is steady. With the software it fluctuates between 700 and 740. If I accelerate slowly it will accelerate with no problems . If I push the pedal rapidly it bogs and runs poorly until the rpm is above 1000 to 1500 when I pull my foot off the pedal rpm drops below 300 for a few seconds then returns to normal at 700 . And some times it will die .It will immediately restart and idle normal .Thank you guys for the help.
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Old 07-18-2021, 01:14 PM   #9
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If you have durametic it would be worth graphing the misfires for all cylinders. With mine they sometimes reset back to zero while I am watching it.

Durametric will show pending codes as set codes so you should see anything there if there are misfires.
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Old 07-18-2021, 01:15 PM   #10
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I have durametrics software .When I got the car it had a Porsche replacement, the original had an ims issue . This motor had low oil pressure when I got it so I replaced it . Car idle is normal at 700 rpm . The tac dose not hunt , rpm is steady. With the software it fluctuates between 700 and 740. If I accelerate slowly it will accelerate with no problems . If I push the pedal rapidly it bogs and runs poorly until the rpm is above 1000 to 1500 when I pull my foot off the pedal rpm drops below 300 for a few seconds then returns to normal at 700 . And some times it will die .It will immediately restart and idle normal .Thank you guys for the help.
Sounds a bit like fuel delivery issues.
Once your at 1000-1500 RPM will it accelerate normally to wide open throttle.????
regardless of whether you accelerate fast or slow???

You may want to do a fuel pressure test at the fuel rail and a fuel volume flow test.
Those tests will tell you if there is a problem with the fuel pump or fuel delivery to the injectors.

Vacuum test is still a good idea so we can start to rule some things out.

When was the fuel filter changed last???

Have you recalibrated the E-gas pedal???

Also look at your throttle position with the Duremetric. work the gas pedal with the Durametric hooked up and see if the signal % open seems right. things like 50% or near when you hold the gas pedal half to the floor. 3/4 pedal to the floor =75 % or close on the software.

Last edited by blue62; 07-18-2021 at 01:55 PM.
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Old 07-19-2021, 03:18 AM   #11
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The fuel filter was done when the heads were replaced .Sorry I have done so much work to this car I forget somethings . I did test gas pedal and the software says it correct . How do you reset the gas pedal ?
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Old 07-19-2021, 05:15 AM   #12
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The fuel filter was done when the heads were replaced .Sorry I have done so much work to this car I forget somethings . I did test gas pedal and the software says it correct . How do you reset the gas pedal ?
To recalibrate e-gas pedal:
With car setting level.
Disconnect the battery for 15-20 minutes this will allow the ECU to drop learned settings.
Reconnect battery.
Turn key to on position for 1 minute.
Do not start.... do not touch the gas pedal.
Turn key off for at least 10 seconds.
Start car.
After you start the car it can take a few minutes for idle to settle in and smooth out because the ECU is relearning some settings.
Take it for a drive and see how it acts.
Let me know if it changes anything.
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Old 07-19-2021, 07:39 AM   #13
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Yes sir .Thank you sir.
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Old 07-19-2021, 08:39 AM   #14
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late to the party - sounds like either a fuel delivery problem or timing is off. in addition to recalibarting the pedal, check your fuel rail pressure. theres a schrader valve on the forward end of bank 1 to hook a guage to. i forget pressures off the top of my head but i wanna say 3 bar at idle and 3.5 at running rpm. also check fuel pump delivery rate. if pressure and pump are ok then i would move on to looking into timing issues.
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Old 07-19-2021, 10:25 AM   #15
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blue62, Stl-986, ike84,

You guys are AMAZING.
Everyone on this forum is so helpful.

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Old 07-19-2021, 01:07 PM   #16
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When you say check timing do you mean pulling the suction pumps and locking the motor and checking the cam index marks? I will have to get a vacuum gauge & fuel pressure gauge .I will report readings when I get them.
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Old 07-19-2021, 01:33 PM   #17
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they aren't suction cups but pressed in seals. That is what I mean.

We are almost in the same boat on similar issues but I refuse to drop a new engine in this thing unless I can get a great deal on one. If it gets to that point for me it's off the cliff with it, selling it or parting it out....all of which for me I am almost there.
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Old 07-19-2021, 02:04 PM   #18
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On one end of the head there is a pump that returns oil to the sump the other end has the cam plugs. I reset the computer and gas pedal it makes no difference . Last Saturday I put a set of new factory coils because Porsche said my after market could be bad .It made no difference putting in new factory coils . I pulled the plugs and they are getting to much fuel smelled of gas . And right now when I started it you can smell gas ?

Last edited by gabedrummin; 07-19-2021 at 02:14 PM.
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Old 07-19-2021, 02:22 PM   #19
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If Cam timing is off by much it will show with a vacuum test.
If vacuum test points to bad cam timing then you can do a compression test to verify the vacuum test.
If your smelling raw fuel hook your Durameteric up and look at O2 signals and fuel trims.
If your running overly rich your O2 signals should show a voltage bias above .450 millivolts.
At the same time your fuel trims should show negative in an attempt to drive the O2 signal below .450 millivolts.

look at the data at idle and then again at around 2500 RPM. Hold each RPM range for a minute to two minutes while viewing the data.

What did the plugs look like????
Wet??
normal light tanish?
grey??
????

What is your fuel mileage like???
Miles per gallon???

Last edited by blue62; 07-19-2021 at 02:27 PM.
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Old 07-19-2021, 03:02 PM   #20
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Smells like gas. Plug has maybe 2k on it.

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