986 'misfire' ? Help!

[whereswilbur]

Hi, I was out in my boxster (1998 2.5 manual) today for the first time in a few weeks. When I started the car it ran fine, however once I got on to the motorway and put the foot down a bit, the car had a kind of hiccup (maybe a misfire) at around 3500-4000 rpm and 70mph. It then ran fine for the rest of my journey (around 2 miles). On the return journey home, the same thing happened and once I was back on the normal roads driving about 40mph it kept doing this hiccup. After a further mile the car kept dropping below 500rpm and cutting out (pulling up at junctions etc). I had the MAF changed about 8 months ago due to a similar rough idling problem, however I used an after market one as opposed to a genuine bosch one. Could it be that my cheaper MAF is causing this problem again? I don't have a fault code reader so cant check for codes. Any help or tips much appreciated! Thanks in advance, Dave.

[Loren]

MAF has almost nothing to do with idle - you can unplug it and your idle will not change.

The MAF does the most work at 4000 RPM and up. If you have a dirty or bad MAF a usual symptom is that it stumbles or won't rev above 4000 RPM.

Most idle problems are a dirty ICV (Idle Control Valve) or sticky throttle butteryfly. Both are usually cured with a good cleaning of carburetor or fuel injection cleaner. Sometimes the solenoid in the ICV goes bad and it sticky or does not move - in those cases you need to replace the ICV. BTW... MY2000 and newer use eGas so there is no ICV on those cars - and they are even more susceptible to dirty throttle bodies/butterflys than the early cars.

Only a guess from your description but I suspect a dirty or bad MAF. You should really read the fault codes to be sure you don't have some other problem or more than one problem.

[whereswilbur]

Cool, I will give the car a check over tomorrow. I will put a bottle of fuel system cleaner through it too. Any ideas on which fault code readers are worth buying? I have seen some on ebay but am unsure what to look for? Thanks, Dave.

[wvicary]

Durametric is the best aftermarket scan tool for Porsche.

[whereswilbur]

Finally got a code reader on the car, but there is no codes stored on the ecu. I'm now beginning to wonder if I have the correct MAF fitted to the car. I replaced the MAF last year with one bought from ebay. When the car is idling it fluctuates between 800 - 1200 rpm. The Indy that serviced it form me had commented that the idle was a little high, but he was unable to get into check it as my roof wouldn't go down at that time due to another problem. However he found no faults stored the time either.

So, my questions are -

1. what is the correct idle speed?

2. can anyone tell me if there is a difference between the MAF sensor on the boxster 2.5 / 2.7 / 3.2 / 996 ?

3. what is the correct part number for the 2.5 MAF sensor?

4. would an air leak cause this fault?

:cursing:

Thanks in advance! Dave.

[tolum]

I cannot help you on your questions but I have to tell you that I have exactly the same problem with my 2003 2.7 Boxster since last year exept my idle that is perfect. No CEL or pending problem codes. On my side I did change my spark plugs thinking it was the problem but it is not. I did clean my MAF that is the new model finishing with 125-01, no change. So before spending more $, I'll be folowing your story to see if you ends up with a solution.

Regards

Thierry

Edited April 19, 2010 by tolum

[kr1572]

I have most likely the same problem. My car is a 1998 Boxster 2.5L manual.

I noticed a few hickups in low rpm's when changing from deceleration or idle to acceleration. Typical at stop-and-go traffic.

Have not noticed any problems above 3000 rpm, only in accel from low rpm's.

I am thinking I will try a cleaning of the throttle and CIV and see if this helps.

[whereswilbur]

I think I will need to try cleaning the ICV too, better get the hardtop off this weekend!

[Loren]

1. For a MY98 Boxster 2.5 liter - idle is 740 RPM + or - 40 RPM

2. Basically they are the same - except eGas was added to the Boxster in MY00. The later style MAF has a 'Z' shaped passage that is supposed to reduce dirt and oil fouling. Your car can NOT be upgraded to the new style MAF (only MY00 on can).

3. Your car's MAF is: 996.606.123.00 MAF. -- Nothing wrong with the 996.606.123.00 MAF - my car has the same MAF. This is the same MAF used on on 3.4 liter Carrera 2's until MY00.

4. Yes, but the fault code(s) would help determine that - not all readers can read "pending" fault codes.

My advice would be to do all the things I suggested in my first response to your question. Clean the throttle body, clean and check the ICV. Get the proper tools to check the MAF voltage.

At this point I suspect a combination of these.

Also, when you take the intake tubing off to clean the throttle body - not if there is oil in the throttle body. That would be a sign of an AOS failure.

[kr1572]

OK, it is me again - I am obviously following this topic closely.

When accelerating in 3/4/5 gear at low rpm (1200 - 1800), the engine hesitates, coughs, does not accelerate smoothly.

No problems with rough idle, and no problems driving over 2000 rpm.

I took out and cleaned the throttle body yesterday, checked the ICV and cleaned it - the barrel moved freely.

There was a little bit oil behind the throttle, I guess that is coming from the crank case ventilation and should be normal?

Next, I filled up the tank today with fresh gas, after runnning it low.

Then I added 3/4 bottle of carburatur / injection cleaner - hoping to clean out any water or dirt from the fuel system.

Also, I checked and cleaned the MAF, it is almost brand new (BOSCH part), as I replaced it during the winter.

To double check if false MAF reading is the cause, I detached the MAF wires, and drove the car for 10 min with detached MAF plug.

The problem was still there...

Going to see if the injections sytem cleaner will help as I am burning the tank in the next days...

Any other suggestions where to look?

[whereswilbur]

1. For a MY98 Boxster 2.5 liter - idle is 740 RPM + or - 40 RPM

2. Basically they are the same - except eGas was added to the Boxster in MY00. The later style MAF has a 'Z' shaped passage that is supposed to reduce dirt and oil fouling. Your car can NOT be upgraded to the new style MAF (only MY00 on can).

3. Your car's MAF is: 996.606.123.00 MAF. -- Nothing wrong with the 996.606.123.00 MAF - my car has the same MAF. This is the same MAF used on on 3.4 liter Carrera 2's until MY00.

4. Yes, but the fault code(s) would help determine that - not all readers can read "pending" fault codes.

My advice would be to do all the things I suggested in my first response to your question. Clean the throttle body, clean and check the ICV. Get the proper tools to check the MAF voltage.

At this point I suspect a combination of these.

Also, when you take the intake tubing off to clean the throttle body - not if there is oil in the throttle body. That would be a sign of an AOS failure.

Thanks for your help Loren, I will get the hardtop off this weekend (the scottish weather is getting a little better!) and check all you have said. I hope I can avoid spending more ££££ on it as its cost me small fortune these last few months!

:renntech:

[whereswilbur]

Ok, I'm still a bit stuck with my boxster problems, I have replaced my MAF, cleaned the ICV, checked for oil in the inlet tubing, checked for air leaks, but still have problems. This time however, my trouble is that the car is idling strangely. it will idle around 800rpm then rise to around 2000rpm on its own, before dropping back to 800rpm and just keeps dong this. any ideas? Thanks.

[Loren]

You have a leak somewhere - have you put a fault code reader on the car?

Better yet the Durametric software so you can read the MAF voltage and airflow.

[sikest]

I had a simular issue with my 02 S. In my case all six of the coils had tiny cracks which caused misfires at random times. The cracks were not immediately visible so I assumed they were okay. I took the car to my local independent and he diagnosed the issue from the drivers seat. After he pointed out the cracks they were pretty obvious. So, new plugs, spark plug wells, new O-Rings and new coils and my Boxster feels new again.

Tony

[whereswilbur]

My fault code reader isn't showing any codes whatsoever. I don't have access to a durametric either. Where should I be looking for air leaks? I have checked all the tube from the air filter to the ICV but it all looks good. :thankyou:

[whereswilbur]

I have added a video to youtube to help!

Edited May 28, 2010 by Loren
made video viewable here

[Wayne R. Dempsey]

Hmm, okay. A couple of things. Your coolant lamp is blinking, which means you're very low on coolant - fill that sucker up before you run it again. The exhaust sounds doesn't sound quite right, do you have an aftermarket system on there? Finally, I have never seen a Boxster do that before, it's like it's hunting, but it's not. I would think vacuum leak or something affecting the vacuum of the system. I've got an article on troubleshooting vacuum leaks here: http://www.pelicanparts.com/techarticles/Boxster_Tech/21-FUEL-Vacuum_Leaks/21-FUEL-Vacuum_Leaks.htm . But, I think you may have additional problems. The car shouldn't do that on its own.

Okay, I just saw that you have a 1998, the problem is most likely with the idle control valve, which is on the side of the throttle body. Sounds like the car is opening the valve and then closing it, trying to get the right metering of air. Maybe a vacuum leak afterall. The only way the car could be revving like that is if the ICV is opening and closing on its own.

Not sure if this helps any...

-Wayne

[Stefan]

Try pushing down on the oil filler cap while it's hunting and see if the problem stops.

[whereswilbur]

Hmm, okay. A couple of things. Your coolant lamp is blinking, which means you're very low on coolant - fill that sucker up before you run it again. The exhaust sounds doesn't sound quite right, do you have an aftermarket system on there? Finally, I have never seen a Boxster do that before, it's like it's hunting, but it's not. I would think vacuum leak or something affecting the vacuum of the system. I've got an article on troubleshooting vacuum leaks here: http://www.pelicanparts.com/techarticles/Boxster_Tech/21-FUEL-Vacuum_Leaks/21-FUEL-Vacuum_Leaks.htm . But, I think you may have additional problems. The car shouldn't do that on its own.

Okay, I just saw that you have a 1998, the problem is most likely with the idle control valve, which is on the side of the throttle body. Sounds like the car is opening the valve and then closing it, trying to get the right metering of air. Maybe a vacuum leak afterall. The only way the car could be revving like that is if the ICV is opening and closing on its own.

Not sure if this helps any...

-Wayne

Thanks for the help, I will check the system tomorrow and see what I find. With regards to the exhaust, I think its original. I haven't replaced it myself at least. However it has only just started to sound different, maybe its on its way out? I have bought a new coolant level sensor as I have topped up the level but the light remains on. I hope I can get all my problems sorted or I will miss out on the Scottish summer time which only ever lasts about 5 minutes!!

[juniinc]

Your coolant light is blinking slowly,,,

Check if your engine compartment fan is kicking on.

[whereswilbur]

Ok, today I replaced my coolant level sensor and the light is still flashing! I will get back out and check the fan. I also unplugged the MAF and the weird idle problem went away, could I have another faulty MAF? When I plugged my old one in the same fault came back. Im thinking a trip to the garage is required!!

[Loren]

You need to put a PST2 or PIWIS tester on this car - it will pinpoint the cause of the coolant light and show the fault code(s) (or pending fault codes) for the misfires.

This is the fast - no guessing solution.

[whereswilbur]

A quick update on the problems! A new MAF was fitted, and I sealed up a few holes in the exhaust. The car is now running and driving sweet as a nut, for now........ :renntech: