Mfletch

Hi Guys, I have previously asked for assistance regarding a continuing problem that I'm experiencing with my Porsche. My check engine light has illuminated several times over the last several months. It will stay on for a couple days and then reset.
When I had the car smog tested it had four stored fault codes. The codes were: P1128, P1130, P1125, and P1123. I have an "Alldata" printout from an independent shop. The printout explains the possible problems indicated by each fault code. They all indicate a possible lean/rich threshold problem.
The symptoms include: severe surge when driving at constant freeway speeds, occasional stalling especially after hard braking, possibly a slight amount of dark smoke coming out of the exhaust under acceleration (i followed the car today and it was almost imperceptible).
The car idles fine and accelerates without a problem. I thought it was a MAF sensor. I replaced the MAF sensor a month ago and the problem persists.
Has anybody experienced a similar problem? Does anybody have any suggestions? If I can't resolve this problem by next week, I will have to take it to the dealer and spend money that I would rather spend on suspension modifications.
I appreciate any advice.

Mfletch

I made an appointment for Monday to have someone else fix this problem for me. I really hate to give up and admit defeat......has anybody else had any fuel related problems with their 996? My check engine light went back on today and the problem appears to be getting worse.

1999Porsche911

Have you disconnected the MAF cable to see if the surging stops?

99firehawk

those faults do not always mean that its a maf sensor.........but .......
first off changing the maf did you install the right maf sensor ?
what part number did you use.
after that you need to check that its installed in the right direction (i have seen it )
check fuel pressure
but im willing to bet that its a vacum leak
make sure the intake is secure to the thotle body.
after that you need to check for a vacum leak
start the car and take off the oil cap, doess the car run diffrent? can you hear a leak
obvvious spots are the intake distrubutor (the t that goes to each plenem)
are the tubes properly fitted ?
oil fill tube leaks at the base or the acoridain
oil seperator bellows the rubbe acoridian under the oil seperator
the plastic acordian that runs out of the oil seperator to crank case after that your gettin into physics

ArneeA

Could it be a misfire also?

Mfletch

1999Porsche911, I only notice the problem at freeway speeds...I'm reluctant to take the car out on the freeway with the MAF sensor disconnected. Do you know if that is advisable? Would that be to rule out me having gotten ahold of two bad sensors?
Brad, I verified with the dealer that I purchased the correct MAF. I was careful to make sure that I installed it with the arrow pointing in the correct direction. I am not finding any obvious signs of a vacuum leak. I had the oil separator replaced about 500 miles ago. The dealer thought that was the cause of my surging problem. The problem persisted after the separator was replaced (by an independent shop). The dealer checked the repair for me about 100 miles ago when they did an alignment..they said it looked fine. Wouldn't a vacuum leak affect idle and acceleration? When the car stalls, it is usually after hard deceleration.
Arnee, if it is a misfire...it is only noticeable at freeway speeds. The fault codes indicate a fuel problem.
1999Porsche911, Brad, and Arnee, I REALLY appreciate your suggestions and advice. Brad, what you said about getting into physics is my fear. I think this one is beyond my ability to resolve. Thanks again guys.

99firehawk

your fault codes tel me vacum leak

Tippy

I would recheck the bellow on the oil seperator and make sure it didnt tear.

ScottArizona

Mark,
Are you still running the old-style evo intake, as indicated in your signature? If so, I bet that very well could be your culprit. I think I can recall hearing from someone that the old style units can kill even a new MAF sensor in a few months' time. Might be worth finding someone with a stock airbox and borrowing a known good MAF sensor to see if the problem exists with this configuration. Good luck.

Chuck Jones

Mark:

I kept the stock airbox from when I installed the EVO CAI...(I keep all the OEM stuff) so if you want to put that in your car to check it like ScottAZ suggested, I can get it to you.

Chuck

1999Porsche911

By simply removing the MAF connection, IF it is the MAF, the surging will stop as the compter will revert to the default maps.

Mfletch

Thanks for all the advice. I wasn't able to make my appointment at the independent shop today. I called the service manager at Niello Porsche (David Welling). He was very helpful as usual. I described my problem to him. He told me to remove the EVO cold air induction system and try the stock assembly. I did and the problem is gone. (Scott you were right. Chuck, thanks for the offer).
The bad news is... now I have a first generation EVO intake that is worthless. I'm going to call them tomorrow and see if they will take back the old intake and give me a break on a new one. I miss the sound of the cold air induction system.
Again, thanks to everybody who offered me advice. I really appreciated it.

ArneeA

^^ EBAY!

Mfletch

Arnee, I thought about selling it on ebay. I bought it on ebay; however, I couldn't sell it to anybody without telling them the problem it caused in my car.

Chuck Jones

Mark: The EVO folks are pretty good fellows...and I wouldn't be surprised that if you were to contact them and explain that their first iteration of the CAI caused you some problems....that they wouldn't try to make some adjustment with you. I've been running my EVO CAI for over a year and have never had any CEL problem except once......when I disconnected it to tighten up the CAI and forgot to put the wire harness back on....then the CEL came on. Funny how that works isn't it? It took about 60 miles after sticking it back on to clear the CEL.

Do you have a stock intake to put on? You can have mine if you need it....Also...check for a PM regarding this issue.