No throttle - lots of codes

[FatherAndSon]

Hi - new owner of a 2003 986 with the 2.7. My issue a series of codes and other symptoms that I think are all related. Stepping on the accelerator does nothing. The car does start up and runs. It idles rough and its revs fluctuate (800-1200). Probably runs a bit rich too. I've run a scanner and it throws all these codes.

P0103 (Confirmed) - Mass or Volume Air Flow "A" Circuit High
P0132 (Pending) - O2 Sensor Circuit High Voltage Bank 1 Sensor 1
P0138 (Confirmed) - O2 Sensor Circuit High Voltage Bank 1 Sensor 2
P0152 (Pending) - O2 Sensor Circuit High Voltage Bank 2 Sensor 1
P0158 (Confirmed) - O2 Sensor Circuit High Voltage Bank 2 Sensor 2
P0223 (Confirmed) - Throttle/Pedal Position Sensor/Switch "B" Circuit High
P1120 (Confirmed) - Manufacturer-specific code (tap to search) Throttle position sensor malfunction
P1138 (Confirmed) - Manufacturer-specific code (tap to search) Throttle position sensor 1
P1140 (Confirmed) - Manufacturer-specific code (tap to search) Throttle position sensor 2
P2135 (Confirmed) - Throttle/Pedal Position Sensor/Switch "A"/"B" Voltage Correlation

Given the majority of these codes indicate a high voltage issue, I'm thinking this is more of a centralized issue than a specific sensor being bad. Of course all of the codes are related to the throttle / air intake/exhaust system. I also found a receipt in the car from last month for installation of new O2 sensors and can confirm there are new ones under the car.I don't know the part numbers of what was installed. Electrical stuff is a weak spot of mine.

I did take the throttle body off and it was reasonably clean. Cleaned it further and reinstalled. I cleaned the MAF and replaced the engine air filter - the old one was disgusting and the foam top disintegrating. One symptom we noticed after replacing the throttle body was that after starting, pressing the brake pedal caused the engine to increase RPM a bit and then stall the engine. Another symptom is that when turning off the car the engine revs quite a bit (and sounds good) just prior to the key clicking over into off. I've swapped the DME relays and nothing changed (panel 2 positions 1&2).

I've checked multiple ground points and they are fine.

I have 3 current theories: 1 the DME may be bad and is sending greater than 5V to these sensors, 2 there is a short to power somewhere (I haven't figured out where a common short to power would be located that effects these 3 sensors), 3 the ignition electrical switch is bad (the better performance right before turning off is my reason).

Anyone have ideas? Also, anyone have the wiring diagram for the 7.8 DME showing the wiring for the MAF and Throttle sensors? I have the Bentley manual but it only has the 7.2 wiring diagram. I imagine they are similar. Thoughts on how I can further diagnose the issue?

[78F350]

Here's what I have available at the moment. DME 7.8 showing pedal sensor to DME.



Maybe find and post more of it later.

[FatherAndSon]

That's helpful. Not only is the layout different but the sensor voltages are different.

[Beelzy]

I had the same issue, it wound up being the DME.

[FatherAndSon]

Thanks. I came to that conclusion over the past 2 days and shipped the DME off for repair yesterday.

I tested the pins of the MAF and throttle connectors with a multimeter and both ground pins had voltage. That caused me to believe the short to power was within the DME. My hope is that a week from now the car will be running fine.

[FatherAndSon]

Originally Posted by Beelzy

I had the same issue, it wound up being the DME.

What company did you use to repair the DME? Mine came back without finding/repairing anything.

[FatherAndSon]

For anyone interested, here is an update.

I replaced the ignition electrical switch (Both my son and I tried from underneath and neither my son who should be more flexible but is bigger or I could do it. We ultimately went through the side vent). That didn't solve anything.

I sent the DME to a computer place that'll remain nameless, they initially said they repaired it but it didn't solve any issues when it was reinstalled. After emailing with the repair place it seems that it tested find when it arrived at their shop and they didn't do anything to it. They refunded me the full amount for the "repair".

I went back to the receipt for the exhaust repair and new O2 sensors and called the former owner and left a message. A few days later he called back and told me the saga with the exhaust shop. He took the car in for a repair to a "hole in the muffler" and was expecting to wait for the repair. While there they told him he needed 2 new O2 sensors. Mentioned that they first got the wrong ones and were having the correct ones delivered. The work they performed was actually a replacement of a 6" section of exhaust pipe from the back of the cat on the passenger (RH) side. In this new section of pipe is the hole for the after cat O2 sensor. When they delivered the car back to him it had the no throttle issue. He had to tow it from the shop to another place and then to a Porsche dealer to have looked at. Dealer told him it would be 5 weeks and several grand to repair. Owner then donated the vehicle and that's how I came to purchase it at auction.

I don't know why they needed to replace the O2 sensor on the LH side. I've pulled all the O2 sensors and ran the engine and that didn't solve the no throttle. I also noticed that the replacements were part number 986-606-127-01. Which are for before the cat (not after) spot and for earlier models (01/02). I don't know if the wrong sensors in the wrong spot could have caused the issue but I have 2 new ones on order. I've also sent the DME off to ECU Doctors to have tested. While it is away, I've been examining the wiring harness looking for anything that could've been damaged when the exhaust was repaired. One possibility is that the sensor connector to the harness is not bolted to the block and slightly relocated from the side to the rear to reach the new sensor hole/location. I'm thinking that the spot where the wires connect into the harness could've been damaged by pulling on it when moving it. I likely need to remove the fuel rail in order to inspect the joint to the harness more fully. I haven't found any other spot where there could be damage. I also tested resistance from the harness connector to the DME for the O2 ground to the sensor connector and I have continuity and very little resistance. That leads me to doubt there is any wiring issues.

I'm hoping that a DME fix and the correct O2 sensors does the trick.

If anyone thinks I'm missing something, feel free to chime in.

[JFP in PA]

This might be a dumb question that you already answered, but what is the car's charging system voltages, both running and not running?

[FatherAndSon]

Originally Posted by JFP in PA

This might be a dumb question that you already answered, but what is the car's charging system voltages, both running and not running?

Not dumb and I don't think I posted. 12.3v off and 14v while running. I don't recall if I took those when I had a fully charged battery. Because I haven't run it for extended periods and starting it to test, I've been putting the battery on a charger.

[Smallblock454]

Did you check P0223 (Confirmed) - Throttle/Pedal Position Sensor/Switch "B" Circuit High

From my understanding this might be the electronic gas pedal, which also has a kickdown switch, if your car has automatic transmission. Also check the connector on the gas pedal and the wiring harness.

[FatherAndSon]

Final update. Replaced the pre-cat O2 sensors with the right part and got the repaired DME back and the car is working. Needed to clear a couple of codes but otherwise totally fine. The only problem was my son was dropped off at college just a couple of days before we got everything so he didn't get to experience the running car. Spent the next couple of days compounding and polishing the car and she looks great.

A couple of more things to do - oil change, new belt, replace a control arm on the front right with worn bushings and I'm basically done.

She's been a lot of fun to drive the last few days.

I'll probably do this all over again - sell this one and buy another one that needs fixing.

Thanks for all the assistance.