vacuum leak questions from newbie
 

Bought our first Porsche a couple of months ago, 1981 911SC with approx. 171,000km and in very very good condition.

Recently had to go in for service because it was running really rough, ended up spending mucho $$$ to have mechanic put in new intake gasket, new fuel injectors etc. Car seemed to be running better but not like it was when we first got it....idle still bounces around between 900RPM-1100RPM, sputters between 3000-5000 rpm when you step on the gas hard, and the idle doesn't drop when I take the oil cap off....when we first got it, it did..which makes me think there is still a vacuum leak somewhere.

Did much searching on the posts here on the forum, seems to point to a vacuum leak but as a newbie I'm looking for some advice from the more seasoned members here on the forum :) Is it a vacuum leak, or is the fuel mixture too rich (also had O2 sensor changed recently as the old one apparently wasn't working), any other possibilities?

Any thoughts?? Thx.

I have to agree with your initial assessment...you probably have a vacuum leak somewhere. There are other possibilities of course, but locating a vacuum leak is the first, quickest, easiest step.

Get a can of carb cleaner or "quick-start" and, while the motor is idling, lightly spray around each intake port and every single vacuum hose connection. If your idle tries to die when you spray one of these connections, you've found a vacuum leak. Fix leak and re-test.

Keep us posted.

I had a similar problem and I thought I had a leak too. Turned out my fuel mixture was way off.

After you check for leaks, I would check that.

Thx for the tips, I'll keep you posted but I'll have to wait until next weekend to give this a try as I'm away for work all week. I was wondering about the fuel mixture thing....you would think the mechanic would have set it properly, but I've also noticed there sure seems to be a stronger gas smell than before when the car is running....

Anyway, all I know is that the new intake gasket fixed the initial problem (small popping sound on deceleration...I forgot to mention that in my first post) but then the sputtering/idle hunting developed. If the mixture is too rich, would that be enough to prevent the idle from dropping when I remove the oil cap?

That was the case in my situation. I was way too rich. Once I brought it down to within spec, it was normal again.

Success!!! Turns out the fuel mixture was too rich.

Didn't have the carb cleaner I needed to check for vaccum leaks tonite, so I figured just for the heck of it to try the fuel mixture and then I would check for vacuum leaks tomorrow. I leaned it out with about 1/2 turn counterclockwise and started to notice the idle levelling off, took off the oil cap and voila! - the rpm's dropped like they were supposed to....took it for a test drive, no sputtering on acceleration, runs like a charm.

Thx for your advice, glad to be back in the land of the living!!

Awesome, good news all around. Now get out and drive that sucker!!!

intake gaskets should be re-torqued once in awhile

How do you adjust the fuel mixture? I have an 86 911. Anybody have a picture of what needs to be adjusted?

How often should the intake gaskets be re-torqued? Just had the new ones put in a month ago....

I bought Wayne Dempsey's book "101 Projects for Your Porsche 911".....it's a fantastic book...fuel mixture adjustment pic is here on page 96 (hope the link works):

http://books.google.ca/books?id=onrWx9_kJmQC&pg=PA95&lpg=PA95&dq=101+proj ects+for+your+porsche+cis+adjustment&source=bl&ots =2L6jQiL8yR&sig=VIb5m6NuA4nhwQ2ELY6iHrDrSEI&hl=en& ei=YB2SSuLiL4uQMdD8wJIK&sa=X&oi=book_result&ct=res ult&resnum=5#v=onepage&q=&f=false

If you are having a similar problem you might want to repost your question. You have a different fuel injection system and I'm not sure the solution for you may be the same.

My response was specific for the 3.0 engine. I don't think you should have to mess with the mixture on the 3.2 engines really. But I don't know as much about them.

sounds like your wrench may not be worth visiting again if you had to pay $$$ and set the mixture on your own........

Yeah, I haven't taken her into another mech yet to get them to properly set the fuel mixture....I've just tinkered with it til she seems to run well again...I think it might be a touch rich still (idle doesn't drop when I pull off the oil filler cap), but at least she idles fine, doesn't sputter on acceleration, etc.

I ran my CIS slightly rich per spec and it was less finicky



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