2000 S Boxster Hard to Start When Warm

[DSPTurtle]

So after searching this forum and many others I am at wits end.  She cranks perfectly fine and after about 30 seconds she comes to life on a few cylinders and then smooths out and runs perfect.  Restart is perfect.  Cold start is perfect.  Only after sitting 20 minutes once hot and I can recreate it every time.  No codes are shown whatsoever.  Here's what I have swapped so far.

1. Crank Position Sensor

2. Purge Valve

3. Fuel Pump

4. Cam position sensor

5. Fuel Pressure regulator

6. Spark Plugs

7. Throttle Body (and did the recalibration)

8. Fuel Filter

9. Engine Compartment Temp Sensor

10. Coolant Temp sensor.

11. Smoke Test / No vac leaks

 

Yes, I loaded the parts cannon up and fired it directly at the car.  What am I not thinking of?

 

[txhokie4life]

MAF sensor?

[DSPTurtle]

Changed that too.  And used Pedro's advice to just unplug and see if the car will start.  No change at all. 😞

[JFP in PA]

Have you tested fuel pressures and delivery rates?

[DSPTurtle]

Hey JFP, this is Jason.  You helped me on the pelican private messages.  Yes, fuel pressures are rock solid within spec.  Especially after changing the FPR on your recommendation!

[DSPTurtle]

A bit of new information after talking to tech support at GIAC...  I was previously told that the computer only looks for the CPS signal to start the car.  A lot of people said that.  But, after talking with the guy at GIAC he suggested checking the O2 sensors.  With all four sensors unplugged, the car starts normally.  I think we are narrowing this down... O2's seemed happy in the Durametric software but I have heard rumors that the data for the O2 in Durametric can't always be trusted 😞

[DSPTurtle]

Well the O2 thing turned out to be a fluke.  Still having the issue.

[DSPTurtle]

So, I unplugged the throttle body and plugged into a spare.  As soon as I turn the key to "on" it commands the throttle plate to full close, even with the engine hot.  With the throttle body unplugged, the car starts fine.  So it seems that the command to close the throttle plate is what is choking the engine when hot.  Anyone seen thing type of behavior?  Is this a computer issue, because it acts the exact same with two different throttle bodies.  (2000 Boxster S with e-gas)

[JFP in PA]

I would suggest checking the engine coolant temp reading using a scan tool, not the dash.  If the DME is getting erroneous coolant temp data, it will act on it as though it was real.

[DSPTurtle]

You are right on JFP.  I am able to read out the different temp sensors and watch them react.  Engine (coolant) 77.25', Intake 41.25' and oil temp 69'.  So the ECU is telling me that it is getting signals in and putting them out through the OBDII port.  However, I am getting a repeatable P1671 (computer monitoring: reset) which Porsche lists simply as "ECM Faulty".  So tomorrow the computer gets shipped out.  I tried swapping the relays in the back to ensure that wasn't the problem and that 1671 keeps coming back.  It is the only code that I can get to repeat.  Everything else is silent.