Idling/ stalling, no pedal response, weird ecu readings
 

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.

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

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???

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.

Never water up there. I thought it was up under the dash? Since it’s drive by wire, unless there’s multiple. The pedal feel is definitely different, I’m going to try that and also unplugging the pedal to see what readings I get.

Disconnected the pedal still says 30% throttle position. With my durametric I’m getting an extremely erratic MAF airflow reading. It’s running extremely rich to the point of smoke coming out of the exhaust (no cats). It bounces up and down at idle like a bad vacuum leak only it’s just sputtering and running horribly.
It seems like it’s trying to adapt to whatever the issue is but is still thrown way off

If the engine is not running smoothly your going to get erratic MAF air flow readings.
The more erratic the engine runs the more erratic the MAF airflow readings will be.

Did you try disconnecting the battery for a few hours???
That will force the ECU to default settings.

Then before you start it re-calibrate the E-gas.
To do that reconnect the battery.
Turn the key to the on position but do not start or crank the engine.
Wait one minute turn key off for 30 seconds.... then restart the car.
See if any of that does any good.

When you say you disconnected the pedal what exactly did you do???

I unplugged the potentiometer under the dash. I unplugged the battery for a bit and it looked like all the fuel trims reset, but still no difference, when I try to clear the codes with durametric they do not go away. That tells me either wiring issue or issue with the ecu, but don’t know where to look.

Should I start testing the grounds to throttle body and MAF? Can I use continuity with my multimeter? I think I found a couple diagrams showing the ground wire for each, and in theory I should have continuity to any ground on the car? The plugs on the ecu look good no corrosion and they’re not loose. I tried wiggling them around to see if a wire on the plug is loose but no resolve. Seems like the wire for the MAF is on the third plug of the ecu from what I’ve found.
Maybe I can test for continuity between the ground on the maf and throttle body as well?

You said your gas pedal felt different.
My guess is that your E-Gas potentiometer has gone south. "But it is just a guess"
there are numerous wires that go to it.
I think your best bet at this point is to take it to a shop that is well schooled in electrical issues with theses cars.

Continuity testing by it's self is not that reliable....... this is why I say that.
Wires are made up of multiple strands.
It only takes a single strand to show a connection "continuity"
So all the strands in a wire can be broken except one... that wire will test as good because it shows "continuity" on the single strand.
But the wire "circuit" will not function because there will be to much resistance from the broken strands.

Continuity test are only reliable if the wire is completely broken "no continuity" or used in conjunction with resistance testing.

So again I think you need a shop schooled in electrics specific to theses cars.
Sorry I can't be of more help.

I appreciate all the input. It does feel different. And it started inching in traffic, it revved way up when I gave it a little gas and then started missing and died. I ordered a used pedal with potentiometer. I’m wondering if it’s still in “limp” mode with the pedal disconnected because it’s getting zero reading and that’s what it defaults to now. I hope I can get it by Thursday. I’m going on a trip and still have the body shop and insurance to deal with. Just want to drop it off and not have to worry about these headaches.
Fingers are crossed that the pedal and a hard reset of everything will correct it.

Just a guess on my part here but.....
With the pedal disconnected the ECU will see conflicting signals from the potentiometer and the throttle position sensor.
they work together..... you probably know this.... but as you press the gas pedal the potentiometer sends a signal to the throttle butterfly to tell it how far to open.
So my guess is if the pedal is disconnected or it has a fault the ECU sees nothing or a signal that does not make sense from potentiometer at the same time it is getting a signal from the throttle position senor. So there is a conflict....ECU's don't like that.

Wish I could be more help but trying to diagnose an issue remotely is very difficult when they are typical issues.
Your problem is far from typical....
Please keep me posted on what you find what the fix is that sort of thing.
You can PM me or just follow up on this thread.
Good luck with it.

I’ll post a follow up when I find some resolve. Poked around at some wires and traced some harnesses. Took the pot out of the car and tried testing the resistance but since there’s 6 wires it was harder to try and figure out what was what. The red and violet wire carries 5v to the gas pedal, and is also connected to the throttle body. I traced it back to the ecu so i at least know that wire is connected properly. I tried jiggling wires around while the car sputtered. The maf is hooked up to the ecu properly. If I could figure out which wires are what on the maf and throttle body I could be sure that they have correct voltage.

I’ll keep poking around at stuff after work until the new pedal and pot arrives

If you DM me your email, I'll send you all the wiring schematics.

My guess it's 1 of 2 things

1 - there are only a few common ground points in our cars. Multiple circuits ground to a single point. If one has become corroded (or damaged - we're you in an accident?), it could effect multiple electronics. This could also be true of wiring bundles - if you were in an accident and a bundle was pinched it could short multiple sensors.

2 - your ecu is shot

I'm hoping for 1, but Occam's razor may be pointing at the second (especially if there are signs of physical damage to the casing)

If I were you, I'd roll her to the body shop and have her totaled. Get the cash and then decide how much its worth to sort this out. That's just my 2c though.

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I pmd you. I have continuity to ground on the 5v and ground for the accelerator pedal. When I measure the 5v and ground wires on the harness (one end of the multi meter in each) I get .84v and 1.20v for each power and ground circuit. If I go from signal wire to ground I get about 4.5v from each harness. There is no continuity to ground on the signal wires.

Is this telling me there’s a short somewhere in the harness? Or is the dme providing no voltage to the pedal because it’s malfunctioning?

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 :)

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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.

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....

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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.

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.

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. :cheers:

Pictures of car pre accident
 

http://986forum.com/forums/uploads02...1680134266.jpg
http://986forum.com/forums/uploads02...1680134317.jpg
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.....

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.

Dude, I remember your car now... You posted pics after the wrap and a bunch of ****************************s gave you **************** about the matte black, right?

I think it's a sweet car myself. Not factory, but very sharp and very unique. That's what custom stuff is all about!

I would take the insurance money, patch her up (you're clearly skilled), and see how much longer she will go. Yes, things will continue to break. Id be curious about a compression test - 140k miles is a lot for any gasser.

Blue is right about the ecu grounding comments - the ecu itself is grounded but it monitors the voltage on the ground to serve as a reference for the grounds that feed into it. That way, sensitive electronics (maf sensors included) that have small variations in their signal voltages due to electrical fluctuations can be "sorted out" by the ecu. It's kind of like running a ****************ty pic through a filter.

However, for the maf sensor, it really doesn't matter too much. In open loop fueling the dme ignores the maf altogether, and in closed loop fueling the narrowband o2 sensors trump the maf input. Sure, the maf readings do matter, but only so that the ecu can ballpark the conditions onto the fueling maps. If it's completely out of whack then it will cause issues, and that is why you saw trouble when you were grounded to the block - there is way too much electrical interference there. But grounding to the chassis is more than likely good enough for just driving and enjoying the car.

Never forget... The enemy of good is better ;)

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Haha fortunately I’ve never posted my car and had any smack talk about it. Seems like the car will be able to be fixed and not totaled out. Bill is $6300 but covered by insurance. I’m planning on just driving it like I have been, it’s been a good car with a few hiccups here and there. Needs some rear wheel bearings and the rims have been bent which has been bugging me so I’ll want to sort that out. Maybe some 18 inch turbo twists would look cool.
I did a compression test like two years ago and if I remember correctly it was 160-165 psi all the way around with the throttle plate closed which from whatever I was reading at the time looked good.