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Old 10-25-2017, 07:37 AM   #1
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996 TB running lean?

Hey guys, I recently bought a 2000 boxster s and have been getting the dreaded p1128/30 codes. I replaced the oil separator and ordered a new maf for it to try and solve the problem, but it keeps coming back. Upon further inspection, it appears that the previous owner installed a throttle body and t pipe from a 996 onto the engine. I'm not sure if he had it tuned or if it even needs it, but I've been getting those codes thrown fairly frequently. Also, the new maf I ordered caused the engine to run extremely rough so I cleaned the old one and put it back in. Does the 996 throttle body require a maf from the 996 or can I run the one for the 986 in it? Thanks for your help.
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Old 10-25-2017, 07:51 AM   #2
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I have an 03 986S with an 03 996 3.6 engine. Both use the same MAF sensor. I would verify by doing parts query for MAF for both engines from 2000 and see if multiple options. Thinking your vintage will be same as well. The true Bosch unit starts with 996....prefix on mine. Computer figures out what slight air/fuel parameters from there.

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Old 10-25-2017, 07:57 AM   #3
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I guess that means I need to track down an intake leak or try a different maf. The intake pipe coming from the air box to the tb is really hard to slip over the tb. Is there a good solution to fix this? I thought about using my heat gun to soften up the hard plastic and re-mould it to the front of the tb, but I wasn't sure how successful I'd be at doing that.
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Old 10-25-2017, 09:26 AM   #4
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Quote:
Originally Posted by Sdav86 View Post
I guess that means I need to track down an intake leak or try a different maf. The intake pipe coming from the air box to the tb is really hard to slip over the tb. Is there a good solution to fix this? I thought about using my heat gun to soften up the hard plastic and re-mould it to the front of the tb, but I wasn't sure how successful I'd be at doing that.
Most likely a vacuum leak. I'm somewhat confused by your comment that your tb boot is hard to fit over the throttle body. That boot should be a 90゚ rubber from tb (i use a serious clamp designed for turbo tubing interface) which then connects to hard tube (plastic/composite or metal if someone has altered induction)...and trajects towards the airbox after at least 1 more 90゚ bend. Between the next 90 (and if still stock) there is a component to the intake pipe called the "snorkel" and it is basically a way to mitigate sound and potentially create some resonance which may have been removed on your car. Get The Pelican book on the Boxster as it is an invaluable resource. I did my entire swap using that book as manual.
In general, the most common areas for vacuum leaks are under the intake tubes (top of engine) themselves---there's several vacuum lines and I would feel around our get flexible mirror under there to see better. (You will be standing on your head here a bit...ie hard to get close enough visually) take your phone and get several pictures to see if anything askew)
One other trick is to get a can of starting fluid and with the engine running (if it's running rough) spray lightly starting fluid around vacuum hoses and vacuum hose (under plenum) connections and throttle body interface and if the rpms change at all you know that you have a potential vacuum leak. The spray will dissipate quickly. Steer clear of open flame. Obviously don't wanna do this round any kind of open spark but your spark plugs and coils packs are down to the sides of the engine so this should not pose a risk. Share what you find. Hope this is helpful.
Bottom line, Any deviation in rpms as result of you spraying tells you that you've got compromised induction either secondary to bad vacuum or pressure.

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Old 10-25-2017, 09:32 AM   #5
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Sounds like I'm missing the rubber boot going from the tube to the tb.
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Old 10-25-2017, 10:51 AM   #6
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Take a look at this thread regarding different MAFs. Being that your car is a 2000S, you might want to check on a couple of things:
need help with air/fuel mixture problems

When I added the 74mm TB, I got a silicone elbow that fit the new TB and replaced all of the stock intake tubing with aftermarket tubing from AirRaid. I was able to get rid of the Heimholz chamber (intake muffler) and improve the intake flow along with insuring that there were no vacuum leaks.
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Old 10-29-2017, 05:12 AM   #7
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I had these codes and it was do to incorrect positioning of the AOS to TB tube. Connection of the tube on the TB fitting.
With a secure connection, vacuum was gone, codes were gone.
I did break down and replace the tube when I started to see some oil weeping out at the TB side of the tube.
Then I replaced AOS as part of preventative maintenance

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