idle at 200rpm...

[miakki]

Hi everyone!!

All of a sudden, my porsche (911 from 1988) behaves very weird, here's the symptoms:

-When started, it idles at about 200-300 rpm, very unsteady.

-If I give it some gas, nothing really happens, but I I give it gas for a little while it slowely (and very unsteady) builds up to higher revs.

-when reached 2000-2500 rpm, everything seems to work fine (and sounds fine), however, as soon as I release the throttle it slows down again to 200rpm, and when driving, if ever below 2000rpm, it starts to sound funny, just like it doesn't get enough fuel.

I have changed both fuel pump relays, but it didn't make any difference.


Now what could this be??

I have seached some in the forums but I haven't found anything.


Many thanks!!

[miakki]

I have read that spraying something called "carb cleaner" somewhere might help..

I'm not english, so could someone explain to me what "carb cleaner" is and where to spray it?

Is there any risk involved in spraying carb cleaner as a (temp. ) solution?


THANKS!

[DW SD]

Did anything lead up to the issue? Is it down on power until 2k rpm? What happens after 2k? Does it have full power or 80% power, etc??

I think it could be a number of issues, we need more informatoin.

When was your last tune-up?

The way I see it, the problem(s) could be air, fuel, compression or spark related. Can you eliminate some of these potential causes:
compression?
bad spark plug wire (s)
bad cap and rotor
mass air flow sensor - maybe broken or bad contacts
vacuum leak.
Idle control valve - seems unlikely.
bad injector(s)
bad fuel pressure regulator

[WydRyd]

I had exactly the same issue! Turned out to be a dud AFM.

Once I replaced that, everything came good, for a short while, then my damn Fuel Pressure Damper tore the internal diaphragm and bled fuel into the intake, causing the same symptoms, but this time it was flooding the engine (black smoke everywhere).

Check the AFM, and if possible, replace your AFM with a known good one to test it out.

Also, hook up a fuel pressure gauge to your fuel rail to verify you are getting 36-38psi at idle. It may well be your fuel pressure regulator, or damper.

[miakki]

Thanks a lot both of you!

I might try changing the AFM myself, otherwise I'll just bring it in to the mechanic.

THANKS!

/M

[Eric P]

miakki

I don't know the chemistry of carb cleaner but it is a spray solvent that can be used on the inside and outside of carbs that disolves old fuel buildup. Sometimes good for cleaning jets, the outside of carbs, etc.

I doubt this is your solution, especially if the problem was sudden.

[David E. Clark]

Originally posted by miakki
I have read that spraying something called "carb cleaner" somewhere might help..

I'm not english, so could someone explain to me what "carb cleaner" is and where to spray it?

Is there any risk involved in spraying carb cleaner as a (temp. ) solution?

THANKS!

"Carb cleaner" refers to any aerosol carburetor cleaner used to remove carbon buildup. This stuff is very volatile and must always be kept away from any open flame. Don't smoke when using it -- it's so flammable even arching spark plug wires can set it off. This volitility is why carburetor cleaner is so effective in helping to locate a suspected vacuum leak. Spray it on the suspected leak and if there is an actual leak the carb cleaner gets drawn into the engine and acts like propane smoothing out engine idle until it gets burned off and the rough idle returns.

[Gunter]

Do Carreras have 2 pump relays?

[miakki]

Thanks!

Well, then I guess carb cleaner isn't my solution..

It's a turbo, which has 2 pump relays.

Thanks!!

/M

[Gunter]

Ah, yes, turbos have 2 relays.
That wasn't clear from the beginning and is a different ball of wax.
Turbo-owners: Chime in.