What next...MAF Sensor cleaned, OAS Ok, no vacuum leaks

[RajinCajun]

1997 Boxster 5 speed, 97K miles --- I have read a whole lot on these symptoms from this site. Still need some advice.

Symptoms: 1) Occasional (read intermittent) hard starts. Cranks for a long time then eventually fires up. 2) Sometimes will start, but soon die before I can get it into gear to move. Idles for maybe 5 sec then dies. Usually, when this problem appears, it last for most of the day on start ups. Then, next day will purr like a kitty cat. 3) Occasionally, like this AM, will start fine, but when shifting from 1st to 2nd, or from 2nd to 3rd, perhaps around 2500 RPM to about 4000 RPM, will run like its only firing on a couple of cylinders. Has never showed this symptom in first gear or at higher RPMs (above 4000 RPM). 4) Occasional puff of smoke at startup. Does not smoke after a few seconds. Have never noticed it smoking any other time. Not very concerned about this symptom except that I think it may, along with some other symptoms point to a bad AOS. For all these symptoms, I have not noticed any patterns, like it has been sitting for a long time, or sitting in high heat, after fueling, etc. No pattern to this madness.

Fault codes that have showed with the CEL in the past: 1) P0444 or P0445 – I can’t remember which one it was. About four months ago, the CEL came on and my buddy pulled the code that pointed to the EVAP canister purge valve. 2) P1128 and P1130. Recently, these codes appeared. I cleared them and the CEL has not come back on. However, some of the symptoms have showed their face again. The hard start has happened, and the lack of power or not firing on all cylinders showed up this AM. Again, no CEL right now, but symptoms are present.

What I have done: 1) Read a whole lot of stuff on this site. Which is primarily why I knew to do the following. 2) Cleaned the MAF sensor with CRC MAF sensor cleaner. 3) Checked for a bad AOS. As far as I can tell, its OK. I do not feel a suction on the oil filler cap. I did not find oil residue on the tube attached to the AOS. Removed the throttle body and gave it a thorough cleaning. It was very dirty! 4) Performed my own vacuum check via my ears and with propane. I was not satisfied with this, so I took it to my buddy who has a shop. I know he has a smoke machine, but I am not sure he used it to check for vacuum leaks. He did not find any either. Both my check and his included the area under the right fender.

Feels like I need to start replacing sensors and/or the AOS. I’ve read about the vapor lock idea, and I can get the car to start, albeit embarrassing if in a affluent location like a nice restaurant. The symptom that really bothers me is the lack of power when it happens. So, all this to ask: Am I on the right track? If I were to start changing out sensors, which ones are first, second, third, etc? What else can I check? Any discussion is very much appreciated as this is my first Porsche and I am only into a few months of our sure to be long-term love affair. Shhhhhh….don’t tell the wifey! :rolleyes: Seriously, I am still a long way out from learning this car. I love it. But these intermittent symptoms are driving me crazy. Thanks all of you for all the communication I have read on this site already. Its absolutely wonderful.

Thanks again!

Brian

Edited July 19, 2010 by RajinCajun

[pgboxters]

I would replace the maf as they dont work for crap when they get old. I replaced mine finally and got rid of the codes after 2 years of cleaning it.

[RajinCajun]

thanks pg....that's where i was leaning. Pretty easy to get to, and seems to be the culprit of a lot of problems as voiced on this site.

Brian

[Wayne R. Dempsey]

Replacing the MAF would be a good start (http://www.pelicanparts.com/techarticles/Boxster_Tech/27-FUEL-Mass_Air_Flow_Sensor/27-FUEL-Mass_Air_Flow_Sensor.htm), but I'm not thinking that the problems your having are related to that. You might want to try disconnecting the MAF when you have these problems to see if the conditions improve. A bad MAF sensor can cause the car to run worse than if it wasn't even plugged in.

Just a guess - sounds like a fuel deliver / starvation issue to me. Fuel pump going out perhaps, or a clog in the tank? Or, too much vacuum pressure in the tank combined with a weak pump? Just guessing...

-Wayne

[RajinCajun]

Thanks for the input Wyane. I don't have time to get to the car until this weekend, but will disconnect the MAF and take her for a short drive. then I'll take a look along the lines of the fuel delivery idea you re proposing. Let you guys know what i find. Also, the CEL came on today on my way home. So, I'll pull them tomorrow and see what they are possibly pointing to. Thanks again.

Brian