woo102

I bought a 2002 996 Carrera 2 cab, 6 speed in September…..first time Porsche owner. Loving it so far.

I’ve done lots of car work in the past, but since this is my first Porsche, I could use some advice.

I’m chasing goofy / non-linear throttle response below 3000 rpm at partial throttle (high vacuum).
The engine isn’t missing, but it hesitates very slightly when pulling away from a stop or it sometimes surges slightly when I push down on the throttle just a little. None of these symptoms are severe….but it’s enough to take away from the otherwise fantastic driving experience this thing gives me.

I’ve covered the basic maintenance so far:
- fresh oil
- new plugs
- new coils
- new O2 sensors
- new water pump
- new motor mounts
- new throttle body (not routine maintenance….but it was cheap enough, and I was chasing goofy throttle response, so I replaced it).

All parts are from FCP euro and are OE or OEM.

Everything I did made it better, but it’s still not fixed.
I bought a smoke tester and checked for vacuum leaks…..and found a few (see pictures).
One leak that is at the elbow of some sort of breather tube above the alternator. (picture attached with red arrow)
One leak from something on the passenger side close to where the manifold bolts to the head. This passenger side leak is coming from something that looks like a vent. (picture attached with red arrow…but the part in question is blurry)
One leak from the drivers side below the alternator. I can’t pinpoint this one yet but it seems like it’s coming from somewhere along the intake runner or where the intake bolts to the head. (picture attached with red arrows)
One leak from the top of the manifold, behind the throttle body, from what I think is the damper or some sort of flap internal to the intake. No picture on this one.

Questions:
-What is the name of the breather elbow above the alternator?
-What is the name of the thing that looks like a breather / vent close to the passenger side cylinder head?
-Any thoughts on what could be leaking below the alternator?
…..and finally…..
Am I just getting to the point where I need to bite the bullet and drop the engine and take the time to ‘reseal’ the leak prone items in the intake system?

All the pictures were from when I was smoke testing but the smoke didn’t show up very well. I put arrow to show where I was having leaks.


Don’t blame me for the headlight covers…they were on there when I bought it

Elbow

Breather / vent on passenger side….zoomed out

Breather / vent on passenger side….zoomed in)

Leak from below alternator.

996love

I like to use the visual parts catalog at AutoAtlanta. It’s great for finding parts when you only know what it looks like.

http://www.autoatlanta.com/porsche-p..._911_parts.php


Edit: if you do decide to drop the engine, there’s a bunch of stuff you ought to do while you’re there.

such as: fuel injectors, AOS (I would recommend the UAOS), VarioCam wear pads, chain tensioners, etc.

maybe even the IMS, too…

sublm8

Elbow above alt is brake booster vacuum. Very common leak, rescue tape is effective.

part on pass head is AOS vent valve. The check valve is likely stuck.

resonance flap is behind throttle body. Usually leaks from the pivot on the front, there is a vacuum line in back that can get disconnected also. Access is via removing the TB and plenum.

dunno what the other leak near alt is.

It’s a little work but by no means does addressing these require dropping the engine

De Jeeper

Leak behind the alt could be the oil fill tube or one of a multitide of vacuum lines that are behind it.

Remove the alt and re-smoke to narrow it down.

woo102

Thanks for the reply’s, they were both helpful.

Looks like I can just tape up the brake booster elbow.
I’ve read of a few people using a 3/4” ID vacuum cap to seal over top of the resonance flap…..which seems pretty straightforward.
Seems like I can clean or replace the AOS breather.

fixing these address the biggest leaks and hopefully resolve my throttle response issue.

The one below the alternator is the smallest leak.
I’ll dig into that one a little more and hopefully fixing that doesn’t require pulling the intake.

if it does require significant work (like pulling the intake), I’ll likely postpone fixing that one until the winter or whenever I want to bite the bullet and drop the engine to do the full treatment of injectors, AOS, IMS (mine is original with 102,000 miles), etc.

De Jeeper

U can reach all the vac lines if u remove the alt. There is decent access.

What u really need to do is test the aos if the breather is wet. I would put this at the top of the 2 do list. It requires an manometer and a fitting screwed into an extra oil cap. There is nothing to fail in the breather elbow, its a one way flap that is allowing excess crank case vapor to expel. Most likely caused by a failed aos or a very loose engine. The aos being the issue 99 of 100 times.

woo102

Sorry in advance for the verbosity….i’m feeling wordy today.



I think I made things better….can’t tell yet since I’ve only taken one test drive and the computer hasn’t gone through its learning cycle yet.



Following the good advice, I pulled the alternator to continue trying to pinpoint the vacuum leak.

After I pulled the alternator, I then, well, while I’m in here, might as well pull the throttle body and crossover tube so I can put a vacuum cap over the damper pivot shaft that was leaking. So I took off the throttle body and crossover tube…..then said, well……the starter is right there….and my starter bendix hangs almost all the time in cold starts……so I pulled the starter.

Struck out with the starter. I couldn’t get the solenoid torx screws to break free, so I couldn’t take the solenoid off to lube anything

I settled for just spraying the bendix from the outside with PB Blaster. Don’t think it’ll do anything since there’s a seal there…..I’m betting my bendix will continue to hang on cold starts. Oh well…..back to the vacuum leaks.



Pulled the oil breather from the passenger side cylinder head. In my original post, I forgot to mention that the leak I saw from the breather was from where the breather seats into the head. It wasn’t leaking from the check valve / vent area.

That thing was a real pain in the but to remove / replace.

I tried to find a new O-rings for the breather but didn’t have the right size on hand. I admitted defeat and put the old O-rings back in……darn. I put a very very thin film of RTV silicone above the O-ring on the breather-to-cylinder head mating surface. I used a tiny bit of RTV so hopefully I won’t pay a penalty for that later.

I taped up the brake booster elbow.

I reassembled all the intake and vacuum components and smoke checked again before installing the alternator.

• brake booster elbow leak fixed.
• Breather leak fixed.
• Intake crossover resonance flap leak fixed

I located the source of the smoke I originally mentioned was coming from below the alternator. The drivers side middle fuel injector has a small vacuum leak. It’s not too big….and I wasn’t diving in that far…..so fixing that sucked will have to wait until this winter (or some future winter) when I pull the engine to do injectors, AOS, IMS…..all that stuff.



I also broke the plastic nipple / bracket for the small coolant hose to the right of the alternator. It was very brittle so good thing it happened now instead of on the road somewhere. Didn’t have a replacement part so I used a metal nipple from Doorman to join the hoses until I can get the right replacement part.



So in summary, I fixed all but the injector vacuum leak.

During the test drive, it felt great. The goody throttle response was not really noticeable. Time will tell if the problem is actually better or if it will return as the computer goes through its learning cycle.



I didn’t mention in my original post (but you’ll see in the pictures) that I have an aftermarket airbox and a K&N air filter. This setup came with the car. I’ve cleaned and oiled the filter. Eventually this setup may have to be replaced by a stock air box if the goofy throttle response comes back. For now, I’m just enjoying the nice intake sound it gives me



On a side note…..man this thing is fun. Modulating the throttle in corners and doing the under steer / oversteer dance is fun as could be with the great steering feel and response this thing has.

I also have an NB Miata with coilovers that is a blast on the same roads…..but this 996 is just a different kind of fun
Might as well pull lots of stuff apart while I’m in here

Failed attempt at lubricating the bendix.

Stinkin brittle plastic. Luckily I had the tapered cone from the RTV to use as a plug after it snapped.

Temporary fix for the snapped coolant hose nipple.

If you look close at the injector, you can see dark coloring indicating a slight leak. I was also able to see proof positive smoke coming out when I smoke tested. Luckily the leak isn’t too big…..so hopefully I’m ok until the winter.

All done for now.

DBJoe996

Ditch the K&N oil filter and get a OE paper air filter box. Those have been notorious for causing problems with throttle response, and over oiling the filter gums up the MAF sensor.

996love

If you like the cone filter (I think they produce a really aggressive sound), you can look for one by “aFe Power”. They make a variety of universal air filters that don’t require oiling.

SleepyCyclist

great job!

smith365film

I have the exact same throttle response issue, along with horrible fuel economy. Did a smoke test and found vacuum leaks at the same elbow piece and resonance tube as your car. Going to replace both parts next week!

woo102

After a few trips, I think things are a bit better but I still have some goofiness in the throttle. It’s not much but it’s just enough to annoy me.

I went ahead and ordered a stock airbox and filter….we’ll see if that fixes it.



for the record, I never had a poor fuel mileage issue.



Also, for the complete story:

I took out the clutch helper spring when I first got the car since I really didn’t like the clutch feel with that helper spring in place.

I didn’t realize at that time that there was a microswitch that sensed whether the clutch had been pushed in at all.

when I took the helper spring out, I liked the clutch but had all sorts of bad throttle response.



Reason: without the clutch helper spring, the micro switch was sometimes closed and sometimes open…..and I learned later that the switch affected throttle response / ignition timing.

I then taped that switch so the computer always thinks the clutch is not depressed…..throttle response was waaaayyyy better….but still had the slight non-linear response that I’m currently chasing.



we’ll see if the stock airbox makes things better.

c didy

That coolant connector always breaks. You just look at it sideways and it breaks. There are alloy aftermarket replacements. Plenty of threads. Good to have it replaced although many just get by with a nipple configuration like you have.

GC996

Woo, don't know if you have aftermarket software on your car, but it can substantially improve your throttle response on a 996.2.

pdxmotorhead

Many have run the K&N style filters but its the Plumbing that causes the problems, suposedly the stock airbox has a better flow curve and give more space between the MAF and the Throttle plate... YMMV

I've run the K&N style that fits in the stock airbox and my Durametric showed similar MAF numbers to stock with paper.. WIth my new motor I'm running a stock air box with paper.. Again YMMV

Enjoy the car they are just too much fun.