It's a good sign that the car is running now. It sounds you just have some bugs to work out. They are probably all or some of the following: bad MAF, dirty plugs, bad 02 sensors. The car is definitely going to start throwing codes soon which will help.

MAF:

In this case he's probably already in the limp home mode. So disconnecting the MAF may have no effect. It may be the MAF and disconnecting it is a very easy check. If the car runs the same or better with it disconnected then it might be the MAF. The maf is a wire that is heated and measures air flow by how much cooling it receives. In english that means there's a little silver wire that gets dirty. If you pull the MAF out using a security Torx wrench and look at it edge on you'll see where the air flows through it. There should be a shiny wire that air flows across. More likely you'll find a wire that's covered at least partially in what looks like gray fuzz. You can clean the gray fuzz off with acetone (nail polish remover), isopropynol (rubbing alcohol) or electrical component cleaner from autozone. It should be nice and shiny again with no residue when you're done. See if that helps at performance.

O2 sensor

My brother had a Ford with an early computer controller. He had very similar symptoms as you. His O2 sensor rusted out of the exhaust and was dangling under the car. The computer thought the engine was running very lean because it was just seeing fresh air. I haven't touched the boxster ones yet, but most people sem to replace all of them at once. Now might be a good time to go back and look at those codes that you had initially and use them to narrow down your search.

Ok, so I cleaned the MAF and replaced the Spark Plug tubes as an excuse to pull a plug, and because, well, it was needed. See pics:

http://picasaweb.google.com/jondirty/Porsche#5474238721316082178
http://picasaweb.google.com/jondirty/Porsche#5474238737675537986
http://picasaweb.google.com/jondirty/Porsche#5474238755226869490

When the MAF was pulled, a cloud of dust erupted, so cleaning it appeared to be a good idea. The spark plug pulling indicated nothing unusual, and the tubes' O rings were definitely in need of replacement, but alas.. the car still isn't running well. It has no power above 3k right now, but it still hasn't thrown a new code yet since I cleared the codes below.. any more thoughts on what to try?

Jon

Check to make sure that the butterfly valve in the intake rear is opening?

in the throttle body?

Booked 2 O2 sensors to NAPA with wiring included, pre-cats, on the recommendation from my neighborhood Audi/Porsche mechanic. I'm going to replace those tomorrow and see if I can't get 'er running respectably..

J

just installed the pre cat o2 sensors. To no avail. The car does not want to rev beyond 3,000 RPM, and I think it's running lean. Next part from NAPA is going to be the MAF. Any other suggestions?

http://picasaweb.google.com/jondirty/Porsche#5476108638238912290

A few ideas...

Fuel pump? Fuel pressure regulator (if the box has one... Not sure)? Fuel filter clogged? Electrical issue resulting in loss of spark or signal to injectors of one bank?

The rear cross-over pipe on the plenum has a butterfly valve that opens / closes with RPM, and I have heard that if that is not operating, as around 3K it really loses power.

That and fuel pressure would be easy things to check.

It runs and drives, just very poorly (considering it was running like a top a couple weeks back) and can't make it past 3k. I manually pulled the throttle cable, thinking that maybe the throttle body blade is stuck or facing resistance, but that didn't help. It's getting fuel and spark, it sounds quite normal at idle. it also has idling problems right after you gas it, but then it quickly returns to a normal idle.

New codes:
P1319 Signal implausible cyl 1-6
P1313 emission related signal implausible cyl 1-6
P1314 emission " "
P1318 " "
P0150 O2 Circuit bank 2 sensor 1
P1316 misfire, emission related signal implausible cyl 1-6
P0102 Mass or volume air flow circuit low input (I unplugged the MAF momentarily to see if there was a difference)

The car won't really get past 1500 RPM now...

A smooth & normal idle would rule out most electrical issues. Could still be the fuel pump/pressure.

when the MAF was disconnected; it ran rich (it smelled of gas and couldn't easily maintain idle). Does that help?

When you say it won't rev beyond 3k, is this while driving or just sitting in your driveway in neutral?

driveway in neutral; i drove it a couple days ago, and it wasn't pleasant. now in neutral it's barely getting beyond 1500. ugh.

Since you've tried the obvious fixes, I really think you need to look at fuel delivery. You should be able to easily test pressure off one of the fuel rails. Most auto parts stores sell the proper pressure gauge. Just be careful since you are dealing with gasoline... don't want you starting a fire! Be prepared for some spillage when you remove the cap from the test port.

Do you think it's worthwhile to pop for a new MAF while I'm picking up a fuel pressure gauge? I've got 93k give or take, and it's a wear item. Also, where is the fuel rail? I've plugged fuel pressure gauges into Schrader valves before on SB Chevy motors, but not on a Porsche....

Jon

OK, signal implausible codes mean you have an open circuit in all the sensors listed. Could be a damaged wire harness, failed sensors or failed DME. These codes definitely indicate a car that runs like poo.

Advice: Stop driving/running the car and isolate and test every listed sensor. Maybe a rodent got in there and chewed things up or a harness got too close to a shiny new set of headers and melted. If you don't know how to do this process, find a good local indy who does. Continuing to run the car might just kill it.

Ok, sounds like the time is right to take it in. I haven't been driving it, just starting it for a minute in the driveway after replacing the O2 sensors, and after swapping in/cleaning the MAF. I'll keep everyone posted. I'll save the MAF replacement for another date. It's easy enough to replace, and I'm sure it'll come due soon.

Edit: I spoke with the local Porsche indy nearby (http://abauer.com/), and he agreed it's probably damaged wiring, MAF, or added the possibility that it's a fuel pump. I get off work at 3 PM daily (east coast hours, baby) so he agreed to take me into the shop and diagnose it while I'm present. I told him what i've done thus far (fuel filter, precat O2's, cleaned the MAF, disco'd the MAF, new spark plugs, tubes, o rings, new air filter) and he tried to, over the phone, narrow it down, but we agreed it's just time to bring it in.

I'll update y'all tonight with his findings, then we'll see what's going to be the solution.

J

Before you do! I've become really interested in your problem and did a google search online for possible issues (looked up "car won't go above 3000 rpm"). Here are some possible problems: Bad coil pack, bad gas, killed cylinder, bent valves, miswired ecu, error with MAF sensor.

For some reason, I really think the MAF is the culprit. One guy was able to fix it just by deleting the error code for the MAF (http://my.is/forums/f88/car-wont-go-over-3-000-rpms-fixed-185321/). The code wouldn't reset on its own via disconnecting the battery.

With that in mind, please try and ask the mechanic to use his diagonstic testing reader. Maybe the code will pop up. If it does, then he can delete it and hopefully it'll solve the problem.

tran

Thanks! I'm still leaning a bit towards MAF, but I don't want to keep throwing money at it just to find out it's something beyond my scope (such as a fuel pump). I highly doubt bent valves or killed cylinder would be it as they're cause a catastrophic failure.

That being said, if it is only the MAF, I'm only being charged for a diagnostic fee that's under $100, and it's about time to have a good 1 over by a pro since I've put 30k on it since the last time anyone other than myself has done any work on it.

Keep your fingers crossed that it IS just the MAF.

Well I brought the 986 into Bauer's in Oakland, and we looked it over for a couple hours. They ran the voltage, and it seems unlikely to be the alternator. The fuel readouts are all good, so unlikely to be the fuel pump. There's no single cylinder not getting spark. Conclusion? Best case, MAF. Worst case? They're thinking the flywheel possibly is misaligned. Said they've seen it before.

Tomorrow we find out if it's the MAF; they have an extra one for testing purposes.

Jon

I've used Bauer Porsche Repair for 5 years . Your car is in good hands. Tell Brian and Chris hi from Lee