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Old 10-19-2022, 03:38 PM   #1
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97 starts but not actually

Have had this problem happen intermittently and have gotten zero help nor seen anything similar before.
Have had the same 3 codes for the last year or so (MAF sensor, O2 sensors, catalyst heaters.)

The car will start fine in the morning, drive to work, no issues whatsoever. Starts fine leaving for lunch then starts fine on my way out after work. Itís inconsistent so hard to replicate but at this point, after driving for the 3rd or 4th time In the day Iíll go out to start the car, itíll crank, turn over, rise up to around 1.2k rpm, then in one smooth motion drop back down and die.

No new codes, no abnormal data, have tried disconnecting the battery for a bit, clearing codes, pedal down, in gearÖ Iím completely out of ideas, Iíve got an Ethos scan tool, not sure if thereís a way to reset the ecm or do anything else.

There is literally not a single thing out of place that would implicate this problem and Iím about to just scrap the car

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Old 10-19-2022, 04:47 PM   #2
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Originally Posted by lindemandude View Post
Have had this problem happen intermittently and have gotten zero help nor seen anything similar before.
Have had the same 3 codes for the last year or so (MAF sensor, O2 sensors, catalyst heaters.)

The car will start fine in the morning, drive to work, no issues whatsoever. Starts fine leaving for lunch then starts fine on my way out after work. It’s inconsistent so hard to replicate but at this point, after driving for the 3rd or 4th time In the day I’ll go out to start the car, it’ll crank, turn over, rise up to around 1.2k rpm, then in one smooth motion drop back down and die.

No new codes, no abnormal data, have tried disconnecting the battery for a bit, clearing codes, pedal down, in gear… I’m completely out of ideas, I’ve got an Ethos scan tool, not sure if there’s a way to reset the ecm or do anything else.

There is literally not a single thing out of place that would implicate this problem and I’m about to just scrap the car
When you say you get a MAF sensor code or an O2 sensor code that really doesn't tell us much.
There are multiple possible codes for any one sensor each code specifies a different issue.
As for catalyst heaters????? no such thing present on these cars.

So if you are still getting codes what are they????
How many miles on it?
What work has been done on the car in say the last six months?
Automatic or manual transmission?
How often do you drive it??
Are there any modifications to it???? like non stock air filter? non stock intake? non stock exhaust??

When the issue happens you say it starts.... RPM rises to around 1.2K then it falls off and dies.
Are you giving it gas at this time?? or is the rise in RPM to around 1.2K all on it's own?

Last edited by blue62; 10-19-2022 at 05:57 PM.
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Old 10-20-2022, 05:08 AM   #3
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Engine wise the car is pretty much stock with about 90k manual trans.

MAF sensor is below value
O2 heaters are below value

Did an oil change and tuneup a few weeks ago but is unrelated as this issue has happened in previous years (pretty much since I moved).

Iíve tried giving the car gas as well as other changes when starting. Rising in RPM is just the sweep as the car starts. Obviously a normal start would crank, start, rise in RPM, then settle at idle.
Instead of settling to idle the RPM just drops and the car dies. Same result after clearing codes, starting again, gas/brake combinations.

The codes seem largely irrelevant given the same codes have been present long before this issue started happening. Also the fact that the car still starts and drives normally any other time with the same codes still present.
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Old 10-20-2022, 06:25 AM   #4
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Originally Posted by lindemandude View Post
Engine wise the car is pretty much stock with about 90k manual trans.

MAF sensor is below value
O2 heaters are below value

Did an oil change and tuneup a few weeks ago but is unrelated as this issue has happened in previous years (pretty much since I moved).

I’ve tried giving the car gas as well as other changes when starting. Rising in RPM is just the sweep as the car starts. Obviously a normal start would crank, start, rise in RPM, then settle at idle.
Instead of settling to idle the RPM just drops and the car dies. Same result after clearing codes, starting again, gas/brake combinations.

The codes seem largely irrelevant given the same codes have been present long before this issue started happening. Also the fact that the car still starts and drives normally any other time with the same codes still present.
So first your codes are very relevant.

Your MAF sensor (Mass Air Flow sensor) is one of the sensors used to tell the DME how much air is coming into the engine. From this the DME then knows how much fuel to add to that air for proper combustion.
If the values are out of spec. your going to be running to rich or to lean causing your catalytic converters to burn up or plug up over time. Also over time other issues will begin to arise.
Like the engine dying issue your having. The DME/ECU simply doesn't know how much fuel to mix with the incoming air at all times.

O2 sensors.
If the heater on an O2 sensor is not working. it has to heat up from the exhaust if it even works at all.
They need to reach around 650 degrees F before they begin to work.
Their job is to report feed back information to the DME about fuel air mixture.
If they are not working or take to long to heat up and begin working.
What happens is your car stays on cold start fueling longer. (overly rich fuel air mixture). Which damages your Catalytic converters. Fouls your plugs and does other damage over time.

So you need to deal with any code related issues. letting them go does damage over time and you get more problems.

When you get codes they need to be dealt with. I can't stress that enough.

The following is just a guess.
But your car has an "IACV" (idle air control valve) on the throttle body. It controls the idle by controlling the butterfly position (air intake) in the throttle body. Your rise in RPM and then dropping of and dying at start up could be due to a dirty, stuck or failed IACV.
They are simple and not expensive to change.
They can also be cleaned and that (at times) works just as well as replacing them.
Use the search function here on the forum and do some research on them.
Just type in IACV.

So your MAF sensor issue or an IACV issue.... or both are most likely to cause your problems.
But you also need to fix any and all the code related issues or your going to have more and more issues and expense over time.

When you get sensor codes that say below value that can be a sensor issue or an electrical issue.
"below value" meaning low current or low electrical signal so there is excess electrical resistance for what ever reason.

Keep us posted on the out come.

Last edited by blue62; 10-20-2022 at 04:54 PM.
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Old 10-20-2022, 08:19 AM   #5
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Subscribed.. you always learn new things :-)
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Old 11-01-2022, 03:32 PM   #6
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If I could also add. When codes are present, take MAF, for example, you cannot believe the data values you see on any scanner as the ECM is programmed to run on predetermined default values to keep the vehicle operable. Look at generic OBD II on your scanner and see if the values are different. You may be surprised. Another thing is to check the freeze frame data to see the conditions under which the codes were set. And third, look at the code setting criteria in service data to find out the conditions and number of ďtripsĒ necessary to set the code as well as what defines a trip. Good luck.
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Old 11-02-2022, 04:42 AM   #7
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Subscribed.. you always learn new things :-)
Likewise.

I want to see if the new guy is going to pony up those codes, considering he's on the most robust 986 forum... a leader among its competitors. Lots of smart people here... someone will have the answer (with the codes, FCS).

COAS, dude, pony up the codes if you want to fix your ****************.

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