Car stuttering...Bad MAF? Engine Misfiring, help! (Fault code P0300, P0301, P0302, and P0303)

[DanMumford]

Hey guys, so my 986 has become stuttery, and struggling to accelerate, I read a few bits online that said cleaning the throttle body and Mass Air Flow Sensor could help, so I removed the plenum and throttle body and gave them a good clean, also removed the MAF and gave that a clean with MAF cleaner, fitted everything back in place and started the car and unfortunately it now sounded like it was misfiring! ?

 

I also read that you can run the car without the MAF connected and see if it improves, so I disconnected the MAF and drove around the block, the car didn't seem to struggle accelerating at all and definitely performed better!

 

So I ordered a new MAF sensor online, as I assumed that would hopefully fix the problem, the sensor arrived today and I fitted it in place in the engine/intake tube, took the car for a quick spin...and the problem is still there! ?

 

I'm now also now getting the fault codes P0300, P0301, P0302, and P0303...

 

Does anyone have any experience with similar issues and know a potential fix? Also any idea why it would seemingly run OK without the MAF?

 

Thanks! ?

[Boxob]

Which MAF did you replace it with? Genuine Bosche?

[PaulQ]

Have you got the correct maf ?  You need the one for non egas cars. 

[DanMumford]

11 minutes ago, Boxob said:

Which MAF did you replace it with? Genuine Bosche?

Unfortunately no, not a genuine Bosch part but a compatible one from Autoparts

Amazon MAF Link

 

It does say it's compatible with the 2.5 986 Boxster...

[mikefocke]

14 minutes ago, DanMumford said:

It does say it's compatible with the 2.5 986 Boxster...

Yea but if I look at the parts Porsche used for the years Autoparts claims that part is compatible with I see several different parts (8!) used by Porsche and even differing ECU code depending on the model year.

Clean your old one and retry. Use MAF cleaner.

If that doesn't work, take a picture of the part numbers on the old one and do a cross reference with equivalent Bosch parts. (Porsche only boxes, sprays a part number on them and charges more through their OPCs.) US cross reference here.

 

[banjo1]

youve got misfire on 1 bank so unlikely your maf as this will affect both banks.

more likely the variocam solenoid.

[stew72]

so if you clear the fault codes and run it with the new MAF disconnected do they come back?

Don't fiddle with anything else until you establish what you've just changed is ok

 

[DanMumford]

7 minutes ago, stew72 said:

so if you clear the fault codes and run it with the new MAF disconnected do they come back?

I'll give that a try tomorrow and see!

 

Seems like it could be a total guessing game, some say it's the MAF, or the coil packs, or the spark plugs, or the oil air separator etc etc...

[stew72]

Does it run badly all the time or only when cold or only when warm?

I'd always recommend making sure what you've replaced is right before looking elsewhere. If disconnecting the old MAF noticeably improved things then I would start there. Disconnecting the MAF makes the ECU apply a map that gives a default airflow hence the engine runs better than if the ECU is receiving erroneous signals from a faulty MAF. Personally I've always found non genuine MAF's on anything a bit hit and miss.

[Boxob]

1 hour ago, stew72 said:

Does it run badly all the time or only when cold or only when warm?

I'd always recommend making sure what you've replaced is right before looking elsewhere. If disconnecting the old MAF noticeably improved things then I would start there. Disconnecting the MAF makes the ECU apply a map that gives a default airflow hence the engine runs better than if the ECU is receiving erroneous signals from a faulty MAF. Personally I've always found non genuine MAF's on anything a bit hit and miss.

This. Revisit your work. Make sure no air leaks have been introduced. Clamps are properly fitted. Pipes property sealed. Given the reports on here I would (and did) only fit a genuine Bosch MAF (about £200). Buy cheap buy twice is relevant here.

[PaulQ]

9 hours ago, Boxob said:

genuine Bosch MAF (about £200).

You can get them for nearer half this if you shop around. 

[brownbox]

I had the same problem, same codes too. tried all the same things as you did and i even got enigine check light. In the end took the throttle position sensor off give it a good clean and so far it's been fine. I should of checked that first as it was making a loud buzzing noise.

[Boxob]

4 hours ago, brownbox said:

I had the same problem, same codes too. tried all the same things as you did and i even got enigine check light. In the end took the throttle position sensor off give it a good clean and so far it's been fine. I should of checked that first as it was making a loud buzzing noise.

Is this relevant on a 2.5 with a cable throttle link?

[DanMumford]

I erased the fault codes and disconnected the new MAF and the codes don't seem to have come back...

I also removed the throttle body and plenum again and refitted both, I can't seem to find any air leaks, but there is a slight 'hissing' sound which I don't know if it's normal or not as I've heard a similar sound on other peoples Boxster videos...?

It's also kind of hard to detect anything as my exhaust (stebro race exhaust, purchased from a BoXa member) is way too loud to hear much by the engine lol

Anyway, I've just ordered a genuine Bosch MAF, so when that arrives I'll update as to whether or not its fixed the issue!

[the baron]

I did the same thing and bought a cheap auto parts MAF, car ran cr*p, replaced it with a genuine Bosch one and car ran fine, its not worth scrimping on these types of parts.

[DanMumford]

The new genuine Bosch MAF Sensor arrived and I fitted it in place, the car has definitely improved and seems to be working/performing much better than before...

I've got no fault codes coming up, but I am still getting a check engine light on in the dash, and the car still seems to have a slight idle problem (going up and down) also to my totally non mechanic trained mind the car does smell kind of fuely/petroly (technical term lol )

 

I've got a new, clearer OBD II device and it's given me this live data after a blast in the car...

 

Quote

Fuel system 1 status --- OL-Drive
Fuel system 2 status --- CL
Calculated LOAD Value --- 0.8%
Engine Coolant Temperature --- 87C
Short Term Fuel Trim - Bank 1 --- 0.0%
Long Term Fuel Trim - Bank 1 --- 32.0%
Short Term Fuel Trim - Bank 2 --- 0.0%
Long Term Fuel Trim - Bank 2 --- 32.0%
Engine RPM --- 904/min
Vehicle Speed --- 0mph
Ignition Timing Advance for #1 Cylinder --- 4.0    
Intake Air Temperature --- 50C
Air Flow Rate from Mass Air Flow Sensor --- 0.4lb/min
Absolute Throttle Position --- 0.0%
Commanded Secondary Air Status --- OFF
Oxygen Sensor Output Voltage (B1-S1) --- 0.060V
Short Term Fuel Trim (B1-S1) --- 0.0%
Oxygen Sensor Output Voltage (B1-S2) --- 0.435V
Short Term Fuel Trim (B1-S2) --- 99.2%
Oxygen Sensor Output Voltage (B2-S1) --- 0.245V
Short Term Fuel Trim (B2-S1) --- 0.0%
Oxygen Sensor Output Voltage (B2-S2) --- 0.435V
Short Term Fuel Trim (B2-S2) --- 99.2%

 

I don't really have any idea what that actually means though, so I was wondering if anyone has any ideas, or understands it better?

 

Thanks!

 

[JoeyH]

your long term fuel trim looks very high to me...

 

regarding the lambda readings, we need to see a graph as although the voltages for both of the pre cat sensors are within range what I can't see is if they are oscilating as they should..

 

 

for all you can tell from that reading you could have one or both of the sensors failed just giving out a static voltage...

graph them at idle and post the results , but from the long term fuel trim I suspect you have at least one failing pre cat lambda, best to replace in pairs so you are in for 2 lambda sensors by the look of it..

 

how is your fuel economy ? ( I suspect poor based on the long term fuel trims)

 

not uncommon for MAF's and Lambda's to need replacing together or in quick succession as when a new sensor gets fitted reading within all the correct parameters , suddenly another fueling related sensor is unable to compensate for the new adjustments..

 

just to throw another ? in there, agree with everyone about the amazon MAF, if you want to go a little cheaper , I fitted a Bremi from ECP for about £68 , they are a quality german manufacturer and supply Merc, VAG, BMW and Porsche with electronic components..

 

get a ''proper'' maf first and see what occurs, I suspect things will improve but not entirely resolve as one or more of your pre cat lambda's are failing / have failed.

[DanMumford]

So I reset the ECU as suggested and then took the car for another drive, these are the live data results afterwards, the fuel trims seem to have adjusted a little bit but the bank 2 sensor 2 still seems high...

 

I'll try to get a graph of the sensors once the rain has died down...

How many O2 sensors are there on the early 2.5 engine?

[Richard Hamilton]

On 8/14/2018 at 8:32 PM, banjo1 said:

youve got misfire on 1 bank so unlikely your maf as this will affect both banks.

more likely the variocam solenoid.

If the P0301, 0302, and 0303 codes come back, I agree with this ^^^^

A dodgy MAF wouldn't give misfire codes.

Your MAF is reading about 14Kg/hour at idle, so that's about right.

[DanMumford]

@Richard Hamilton These readings are with the new genuine Bosch MAF as mentioned above! ??

[Richard Hamilton]

I got that, but what I was saying is that if the P030x codes and rough running come back, I think you should be looking elsewhere. I'm not convinced that changing the MAF was the cure.

BTW, the UK 2.5s only have pre-cat lambda sensors.

[ooid]

On 8/26/2018 at 7:06 PM, Richard Hamilton said:

A dodgy MAF wouldn't give misfire codes.

 

Nope, it would. My old car had a very similar issue, could not diagnosed for days (cleaning throttle and etc..) then OPC checked it , and they officially confirmed that new MAF needed! Bosch would do it.

In Op's case; I would assume it could be vacuum leak, Aos or solenoid valve if misfires are still happening after MAF change.

When you checked the throttle again, did you find more oil in there? If so, AOS might be gone. For vacuum leak, it could be anywhere really, your car is too old now, those flimsy plastic bits are already end of their life.

[Richard Hamilton]

It wouldn't give MISFIRE codes (P030x).  It would give EMISSIONS related codes.

[ooid]

On 8/28/2018 at 6:19 PM, Richard Hamilton said:

It wouldn't give MISFIRE codes (P030x).  It would give EMISSIONS related codes.

Hi Richard,  mine was giving P0300, P0301, P0302, and P0303 too. OPC diagnosed as BAD Maf, and really sorted afterwards. I would post the invoice and description If I still have it  

I do not think they are super-precise (the codes) depending on the situation.

[Richard Hamilton]

I would be really interested to see the OPCs diagnostic results if you have them.  I'm always happy to learn something new, but.........

P03xx codes are related to ignition.  I can't see why a bad MAF would cause a misfire, especially on one bank only.  Even if it was causing a combustion misfire, it would affect both banks equally.  To have misfires on all cylinders of one bank only indicates a component common to the bank.  On UK DME 5.2.2 (2.5 Boxsters) the MIL is not triggered by a faulty MAF.  A bad MAF usually produces P112x Oxygen Sensing codes on both banks. 

Sorry to be a pedant.