Bob M

My '02TT "stumbles" under full throttle -- this starts around 4K to 4500K RPM. I also notice that it doesn't develop/hold full boost. If I am easy on throttle inputs and as such don't get into the boost, the engine goes through the full rpm range without a problem. Any ideas as to what might be causing this? Plugs? DV's, MAF? Thanks for the help!

wross996tt

plugs...

adam_

How many miles on the plugs? Any mods?

Bob M

Thanks for the opinion Statman. I was thinking the same thing, though the fact it didn't do it with less than full throttle, was making me think it could be a sensor/computer issue. I will go ahead and try changing the plugs. Any opinions as to the best plugs to put into it -- stock, aftermarket?

Adam -- the car has about 32K on it. I changed the plugs about 10K miles ago. Motor mods are mild,
2nd generation Unichip (originally thought this was the problem, but by-passed the Unichip and the problem remained), BMC Filter and Fabspeed exhaust system (straight pipes off the 100 cell cats is the current set-up). Other mods not related to the motor: LW Flywheel and Sachs Sport Clutch, PSS9's, H&R sways, SS Brake lines, monoballs up front, strut brace up front, Performance Friction full floating rotors up front and B&M Shifter. The cars has been aligned and corner balanced by a great race tech and handles really well. The motor normally works great, but now that irritating stumble.

Thanks again for the reponses.

mikerosi

Hey Bob. I just had the same prob on my car, and after changing out the plugs, it turned out to be the MAF. I had no cels and internal codes and after changing the MAF it ran flawlessly. If you have access to a spare maf that you can install, and it cures your prob, there`s your answer. I was astounded by the lack of codes and cel on my faulty maf, but it was faulty never the less.

wross996tt

Bosch FR6 plugs will work.

Mike, how do you know no codes.....did you use a PST2 or PIWIS or Durametric....without those you might not catch the codes. Also I always suggest this...put the old MAF back in and see if you can reproduce the poor performance...if not you didn't find the cause (simple failure analysis).

Anyway, it does not sound like a MAF to me...FWIW. Just in case get the codes read.

Bob M

Mike, sounds like the same situation -- no cel's or codes popping up on the display. That being said, I agree with you, Statman, you really need a reader to see if something is wrong. I had the 30K service done last December and asked them (local dealer) specifically to check the maf. According to them, it was okay. Anyway, I don't have a spare maf around, so making a swap to compare is out. One of my new Porsche buddies in CA, who is a very experienced mechanic, suggested plugs too, so I think I will give it a try.

If that doesn't do it, then I'll have someone check the maf again and check for codes. If I need a new maf, Hitachi or stock? Any strong opinions on this? I might go ahead a change out the DV's too. I'd welcome some opinions here too.

Thanks again guys -- your feedback is greatly appreciated!

andymac

I have a similar problem. Had a new MAF but this didn't cure the problem. I'm upgrading the dv's and hoses but more for the future remap.
Thinking of changing the plugs and might do the coils as well, going to use the 997TT coils.
Only thing is , the plugs were installed by an OPC a year ago and only covered 3k miles

wross996tt

Bob: get the regular MAF (996 606 124 00)...hitachi needs ecu reprogramming to use and if you have the stock intake...no need. DVs are preventive maintenance and a good idea.

andy: plugs are a funny thing and can go quickly especially if you have and mods.

Bob M

Statman -- Thanks again for the heads up. Got a good plan now.

mikerosi

Hi Wross yes I have the durametric. I drove to Carlson in CA and the Porsche factory tool did NOT read any codes. The mechanic replaced the MAF on a huch and presto...problem solved. This to me proves that the Maf can be a problem without knowing it. The mechanic said those Porsche mafs can develop voltage problems without throwing codes, as in my case. I am just saying, if you have an extra or available MAF, try it and your prayers may be answered. My car was bogging at 5000rpms and I thought for sure it was plugs or a boost hose. This all happened AFTER I upgraded to a 575HP package. Weird but true

wross996tt

mike...did you try putting the old maf in? My guess ....no...my position...you still don't know. I say bs on the maf...but that's me.

mikerosi

Wross, yes we put the old maf in and it does not work! Still stumbles, also runs rich, a lot more smoke on start up because of rich condition, and a slightly rough idle. NO codes on the durametric or Porsche diagnostic tool. We put the new MAF in and car is running perfect. I do not want to sound melodramatic but this is living proof that sometimes a bad MAF will throw ZERO codes. If you need further proof you can call Carlsen Porsche in Atherton, CA and ask for Christian, the head turbo tech and he will tell you the whole story.

wross996tt

OK you win...although I will argue...you have an n=1 sample size. This proves absolutely nothing....(BTW you can't prove anything)

The funny part is, I have lost >3 mafs and the car actually performed fine (although it did throw codes and went into limp mode). In fact you can run the car without a maf and not get the symptoms you speak of. The car will be in limp mode, but will still run fine.

adam_

You might also try electronics or MAF cleaner and see if that has any effect. If it does solve it, great- if it slighly improves then you know it probably needs a MAF (cleaner will remove the oily residue on the MAF, but not baked on/oxidized stuff)

A