Idling/ stalling, no pedal response, weird ecu readings

[ecp]

I was sitting in traffic and all the sudden the car started sputtering and stalling. I barely could pull into the gas station 10 feet in front of me. I am getting zero response from the gas pedal. I pulled the engine cover while waiting for a tow and the throttle body initializes for a second but doesn’t move with the pedal. I pulled up my durametric and got
P2135 accelerator pedal potentiometer
P0123 accelerator potentiometer 1
P0223 accelerator potentiometer 2
P1120 throttle plate
P1138 throttle position sensor 1
P1140 throttle potentiometer 2
P0103 hot film MAF sensor
P0132 o2 sensor before cat
P0152 o2 sensor before cat
P0138 02 behind cat
P0158 o2 behind cat

Sounds to me like all of these are connected in a circuit that’s shorted out somewhere.
Pedal value is 30.08%
Pedal encoder potentiometers are reading 4.54v
Actual value throttle is 118% even though it’s fully closed
Throttle position sensor 1&2 are both getting 5v

I’m truly at a loss. I pulled my ecu and everything looks okay nothing obvious, I saw some weird cracking but not sure if it’s just age or what. This car is supposed to get in the body shop the end of this week and I still don’t even know if it’s going to be totaled out or not. Would love to get back running again. Any help will be greatly appreciated.

[blue62]

Originally Posted by ecp

I was sitting in traffic and all the sudden the car started sputtering and stalling. I barely could pull into the gas station 10 feet in front of me. I am getting zero response from the gas pedal. I pulled the engine cover while waiting for a tow and the throttle body initializes for a second but doesn’t move with the pedal. I pulled up my durametric and got
P2135 accelerator pedal potentiometer
P0123 accelerator potentiometer 1
P0223 accelerator potentiometer 2
P1120 throttle plate
P1138 throttle position sensor 1
P1140 throttle potentiometer 2
P0103 hot film MAF sensor
P0132 o2 sensor before cat
P0152 o2 sensor before cat
P0138 02 behind cat
P0158 o2 behind cat

Sounds to me like all of these are connected in a circuit that’s shorted out somewhere.
Pedal value is 30.08%
Pedal encoder potentiometers are reading 4.54v
Actual value throttle is 118% even though it’s fully closed
Throttle position sensor 1&2 are both getting 5v

I’m truly at a loss. I pulled my ecu and everything looks okay nothing obvious, I saw some weird cracking but not sure if it’s just age or what. This car is supposed to get in the body shop the end of this week and I still don’t even know if it’s going to be totaled out or not. Would love to get back running again. Any help will be greatly appreciated.

Throttle position sensor and the throttle potentiometer could be on the same circuit.
But O2 sensor and MAF with the above??? very doubtful.
I would look at a wiring schematic and see if they have a common ground.
A bad common ground for the circuits or for the ECU "could" cause your issue.

[ecp]

Originally Posted by blue62

Throttle position sensor and the throttle potentiometer could be on the same circuit.
But O2 sensor and MAF with the above??? very doubtful.
I would look at a wiring schematic and see if they have a common ground.
A bad common ground for the circuits or for the ECU "could" cause your issue.

I saw another thread where the issue looked to be pretty identical to what I’m experiencing, from 2007, they said they re established the ground from the MAF which was pin c9 on the ecu, but I can’t seem to find the pin out for the ecu anywhere, and also don’t really understand what it means exactly.
When I unplugged the MAF the car wouldn’t fire at all.

I reset the codes and the o2 sensor codes went away but everything else remained. I highly doubt this is something as simple as a fuse but I suppose I should check them just for good measure

[blue62]

Originally Posted by ecp

I saw another thread where the issue looked to be pretty identical to what I’m experiencing, from 2007, they said they re established the ground from the MAF which was pin c9 on the ecu, but I can’t seem to find the pin out for the ecu anywhere, and also don’t really understand what it means exactly.
When I unplugged the MAF the car wouldn’t fire at all.

I reset the codes and the o2 sensor codes went away but everything else remained. I highly doubt this is something as simple as a fuse but I suppose I should check them just for good measure

Interesting that your car will not start with the MAF unplugged.
Every Boxster I have heard of will run with the MAF unplugged.

You can check your MAF wiring with a Multi Meter so you could check it's ground that way.
You can also bring it up on your Durametric and look at voltage and if you know what to look for and how to compare it to other signals like throttle position you can test it's function.

You would have to look at the wiring schematics to figure out pin outs and grounds for various circuits.
Pin outs:
On the harness connection to the ecu each wire has a corresponding connecting point to the ecu.
those corresponding points are called pin outs....they are also coded similar to your fuse box...so say your looking for fuse A1 so that would be row A and 1 would be the first fuse in row A... Harness connections are set up a similar way.

Try recalibrating your E-gas (gas pedal) see if that will do anything to your throttle position codes and your potentiometer codes.
Have you every had any water get into your interior???

[ecp]

Originally Posted by blue62

Interesting that your car will not start with the MAF unplugged.
Every Boxster I have heard of will run with the MAF unplugged.

You can check your MAF wiring with a Multi Meter so you could check it's ground that way.
You can also bring it up on your Durametric and look at voltage and if you know what to look for and how to compare it to other signals like throttle position you can test it's function.

You would have to look at the wiring schematics to figure out pin outs and grounds for various circuits.
Pin outs:
On the harness connection to the ecu each wire has a corresponding connecting point to the ecu.
those corresponding points are called pin outs....they are also coded similar to your fuse box...so say your looking for fuse A1 so that would be row A and 1 would be the first fuse in row A... Harness connections are set up a similar way.

Have you every had any water get into your interior???

I had some rain water get in way over a year ago but I removed all the carped and cleaned and sealed. It was just a little water behind the seats, nothing got to the immobilizer.
It hardly runs as is because all the readings on the sensors are out of wack. The reading I’m getting on the MAF is like when it’s unplugged….. reads -40c for intake temperature. There’s gotta be some common wire for the MAF, e gas and throttle body.

I’m getting 5v on the MAF and throttle position sensor, 30% pedal value. Throttle body does not move with pedal, reads actual throttle position at 118%. I just don’t know what would make it go out sitting in traffic. It’s been dry here for quite a while, and the car was running fantastic earlier in the day

[blue62]

Originally Posted by ecp

I had some rain water get in way over a year ago but I removed all the carped and cleaned and sealed. It was just a little water behind the seats, nothing got to the immobilizer.
It hardly runs as is because all the readings on the sensors are out of wack. The reading I’m getting on the MAF is like when it’s unplugged….. reads -40c for intake temperature. There’s gotta be some common wire for the MAF, e gas and throttle body.

I’m getting 5v on the MAF and throttle position sensor, 30% pedal value. Throttle body does not move with pedal, reads actual throttle position at 118%. I just don’t know what would make it go out sitting in traffic. It’s been dry here for quite a while, and the car was running fantastic earlier in the day

The water issue:
I was more wondering if things got wet around the base of the gas pedal.
That is where the e-gas (potentiometer) is.

try recalibrating the throttle see if it has any effect.
And or disconnect the battery for an hour or so and see if the ECU will reset with default values.

5v is usually reference voltage .....the signal voltage from the ECU.

[Starter986]

The only thing I can recommend is cancelling the body shop appointment.

[ike84]

I'm not very good with circuit testing, and my girl is put away for the winter (yes, we still have snow on the ground) so I cant give you any reference values. Maybe someone can post theirs for comparison?

I can tell you for a fact that the car should start and idle normally with the pedal harness disconnected. I know this from when I played around with a pedal commander type device - you will just have a dead pedal.

Typing all this out makes me remember a video I saw a great while back - someone noticed that their potentiometer was sticking and acting up so they disassembled and lubed everything and that fixed the problem. If your pedal has a "different feel" that could be another possibility (sorry, I missed that post or I would have mentioned it earlier). Something maybe worth trying would be to disconnect the pedal and then fire her up. If she idles smooth, you have your problem.

If it is the pedal, 78f350 can probably pull one for you and ship it to you for a reasonable price. He even throws in a bonus goodie

Sent from my SM-N975U using Tapatalk

[ecp]

Originally Posted by ike84

I'm not very good with circuit testing, and my girl is put away for the winter (yes, we still have snow on the ground) so I cant give you any reference values. Maybe someone can post theirs for comparison?

I can tell you for a fact that the car should start and idle normally with the pedal harness disconnected. I know this from when I played around with a pedal commander type device - you will just have a dead pedal.

Typing all this out makes me remember a video I saw a great while back - someone noticed that their potentiometer was sticking and acting up so they disassembled and lubed everything and that fixed the problem. If your pedal has a "different feel" that could be another possibility (sorry, I missed that post or I would have mentioned it earlier). Something maybe worth trying would be to disconnect the pedal and then fire her up. If she idles smooth, you have your problem.

If it is the pedal, 78f350 can probably pull one for you and ship it to you for a reasonable price. He even throws in a bonus goodie

Sent from my SM-N975U using Tapatalk

It runs different, but still bad. Same with the maf when I unplug it. Then when I press the brake it shoots up to 2k rpm smoothly and shuts off. I saw the thing about cleaning the pot. I got a new to me low mileage one arriving tomorrow. Doubtful it’ll fix the issue. I was reading a thread on renntech that seemed to be describing exactly what I’m experiencing but it seems the conclusion was the dme was faulty.

I’m going to try unplugging maf throttle body and gas pedal and starting and seeing what happens. When I unplugged the maf it seemed like it was trying to adapt and settled on a steady chug instead of constant misfires. Oddly enough I got zero misfire codes.

Should probably pull the firewall behind the seat and look at the harness for anything obvious.

[ecp]

I ran a hardwire from the MAF ground to chassis. Throttle body initialized, car fired right up. Smooth sailing from here? I’ll have to attach it properly but this seems promising. Breathed a sigh of relief when it started.

[ike84]

Originally Posted by ecp

I ran a hardwire from the MAF ground to chassis. Throttle body initialized, car fired right up. Smooth sailing from here? I’ll have to attach it properly but this seems promising. Breathed a sigh of relief when it started.

NICE!

Damn mice....

Sent from my SM-N975U using Tapatalk

[blue62]

If you go back to my first post to you.....
a possibility of a common ground issue was mentioned..
These cars have different 14 ground points...
I see you got it fired up by running a jumper ground to the MAF.
I think the MAF grounds via the ECU but I am not positive.
The MAF is also two sensors in one.....
One measures air temp. the other measure air mass.
I do not know if they both ground via a common ground or not.
A wiring diagram would show you.
If the MAF does ground via the ECU you have and ECU ground issue.
If you have a ground point issue chances are your going to have further issues with the car.
You need to go through your ground points and the ECU ground point to avoid that possibility.

[ecp]

Originally Posted by blue62

If you go back to my first post to you.....
a possibility of a common ground issue was mentioned..
These cars have different 14 ground points...
I see you got it fired up by running a jumper ground to the MAF.
I think the MAF grounds via the ECU but I am not positive.
The MAF is also two sensors in one.....
One measures air temp. the other measure air mass.
I do not know if they both ground via a common ground or not.
A wiring diagram would show you.
If the MAF does ground via the ECU you have and ECU ground issue.
If you have a ground point issue chances are your going to have further issues with the car.
You need to go through your ground points and the ECU ground point to avoid that possibility.

The diagram shows one ground wire from the MAF so I’d assume they both share that ground. It also shows it grounds via ecu. I’m not sure if the ecu has a ground that goes to to chassis in which all are connected or what. I do have continuity from ecu harness and maf ground but I will check the resistance and try tracing the wire to make sure it is fully in tact tomorrow. It may be a bandaid fix but if it can make it to the body shop I will be thrilled. Could still be totaled out by insurance….. got my work cutout for me tomorrow.

[blue62]

Originally Posted by ecp

The diagram shows one ground wire from the MAF so I’d assume they both share that ground. It also shows it grounds via ecu. I’m not sure if the ecu has a ground that goes to to chassis in which all are connected or what. I do have continuity from ecu harness and maf ground but I will check the resistance and try tracing the wire to make sure it is fully in tact tomorrow. It may be a bandaid fix but if it can make it to the body shop I will be thrilled. Could still be totaled out by insurance….. got my work cutout for me tomorrow.

I forgot all about your insurance.... totaled or not totaled out situation.
So your bandaid fix makes more sense at this point.
If there are circuits that get their ground via the ECU then the ECU has to be grounded to the chassis in some way.
ECU ground issues are not that uncommon.
If you go to youtube and look up scannerdanner he has some video's on diagnosing the issue.
He is a very good source of diagnostic information.

[ecp]

Originally Posted by blue62

I forgot all about your insurance.... totaled or not totaled out situation.
So your bandaid fix makes more sense at this point.
If there are circuits that get their ground via the ECU then the ECU has to be grounded to the chassis in some way.
ECU ground issues are not that uncommon.
If you go to youtube and look up scannerdanner he has some video's on diagnosing the issue.
He is a very good source of diagnostic information.

Thank you, I got a ground cable working, some weird stuff is going on. Looks like only part of the MAF is working properly. I get airflow and intake temp readings but on my durametric hot film MAF reads 0v and there’s a stored code inside.

[blue62]

I am unsure why the Durametric shows Hot film type MAF data when hooked up to our cars.
Our cars use A Hot wire type MAF. not Hot film type
So 0v on the Hot film data "may be" what you want to see.
Just depends on how the Duramatic software is set up
I have always disregarded the hot film data and just looked at the other MAF data.
If your getting air temp. data and Mass Air flow data then both parts of the MAF are working.

[ecp]

Originally Posted by blue62

I am unsure why the Durametric shows Hot film type MAF data when hooked up to our cars.
Our cars use A Hot wire type MAF. not Hot film type
So 0v on the Hot film data "may be" what you want to see.
Just depends on how the Duramatic software is set up
I have always disregarded the hot film data and just looked at the other MAF data.
If your getting air temp. data and Mass Air flow data then both parts of the MAF are working.

Got everything buttoned up and she drives great!!!! New pedal is so much smoother and feels like it has much more travel. Feels great. I checked everything after filling up and driving around for a bit and the ecu is adapting and adjusting fuel trims properly. Everything looks normal and functioning well.

One note about the wire, I initially tried grounding the wire to one of the ground points on the front of the engine block, however, I noticed it wouldn’t run smooth on that ground, and there were stored codes still. I changed the ground point to the chassis. There’s a bolt hole in the body right near the MAF so I grounded it there using a bolt. Reset everything and calibrated throttle and it started up and ran flawlessly.

I don’t know if I’ll end up with this car, I sure love it to death. Considering it’s got 140k miles I might just leave the bandaid fix until it blows, or maybe it’ll go for another 50k miles who knows. Either way, I’m glad I could sort the issue in time, and can drop it off and enjoy my trip. A lot of blood sweat and money in this thing.

[ecp]

surely not everyones cup of tea, but man was I proud. full colored ppf wrap done myself. only had it for a month before the car got hit. Do you guys think it's worth trying to keep? so many new parts all new suspension, lots of engine work, relatively new clutch, 987 custom seats full power and heated, cruise control and Bose sound with upgraded amp and speakers, new transmission, big sway bars, borla exhaust. I just wouldn't be able to replace it for whatever insurance would pay I'm sure. or I could save my pennies for a 996.....

[Gilles]

Only you know how much money and effort has been put on this car, I don't know the extent of the damage but perhaps is best to let the insurance company write off the car, and then buy it back from them..

With the money left, you can start saving for a 987BS, after driving the 986 you would not like the 996.. yes it's bigger but that's it..

[ecp]

Originally Posted by Gilles

Only you know how much money and effort has been put on this car, I don't know the extent of the damage but perhaps is best to let the insurance company write off the car, and then buy it back from them..

With the money left, you can start saving for a 987BS, after driving the 986 you would not like the 996.. yes it's bigger but that's it..

It’s minor damage. Need new hood and bumper cover. A lady backed up into me in a drive through. The trailer hitch hit the front of the hood and it buckled. It’s all bowed up. Pushed the frunk in about a quarter inch where the hood latch is. The work on the tub is what I think will total it. Ballpark 6k repair bill. Since I’m not at fault and have a police report I’d like them to handle it. However if they’re not going to give me anything for the many thousands in parts I have on the car then I will fight as much as I can. I know book value is about half of a decent 986 these days without the kind of work I’ve done to mine. A the end of the day fixed or not it’s a rolling total, but man it sure does drive perfect. Except for when it breaks.