Whuddup.

I have a '99 that idles a bit rough. It has 65k miles on it, but when I bought it with 54k I noticed it then, too. I had the sparkplugs changed, and it didn't affect the idle. It doesn't have a leaking RMS, nor has ever had the problem associated with the 3.4. When the old plugs got taken out I inspected them, and one of them smelled kind of funny. It's hard to describe the smell besides, "funny." They all looked similar, and none had visible problems.

Any ideas?

 

A bit rough compared to what? Have you sat in other 996s to compare? They tend to idle very differently than most "regular" cars. As far as a spark plug smelling "funny", I'll refrain from commenting

 

A bit rough compared to the '00 Carrera that my dad owned. A bit rough compared to the '02 x-50 he owns now. A bit rough meaning it the car vibrates too much at idle...and also it idles lower than it should...therefore it is idling a "bit rough."

comprede?

 

If the idle is lower than normal, check the Idle Control Valve on the side of the throttle body. Also, the temperture sending unit (directly below the air filter housing on the water pump) is known to cause these problems. Both can be slightly out of spec and not cause a CEL. Check all vacuum lines and throttle body connections for leaks. If you have a scanner, hook it up and see what the sensors might be telling you at idle. If you don't have a scanner, get one.

 

OK, that's a bit more clear. I don;t know if there are known idle roughness issues but I can tell you that my 1999 996 idled roughly compared to my 2004 with X51. It may be something inherent to that engine and its programming considering that it's a drive by wire, not e-gas.

 

Alon - Yeah, lol...I'm not a "new" Porsche owner, or anything. There is definetely something wrong with her as sometimes while idling at a light if you pick a note and sing monotonously it will be like yer talking into a fan.

Okay...well not that bad, but pretty bad irregardless. And, it is a 6-spd, btw.

The rough idle is not really consistent with certain type of driving, or only when it is cold. It just seems to idle rough when it wants to idle rough.

1999Porche911 - Okay, so on the "Idle Control Valve" on the side of the throttle body...what am I looking for in particular? Should I remove it and see if it is clogged? Should just replace it? Honestly, I don't mind spending money if it completely eliminates the possibility of that being the problem. (Unless I just check it for something in particular)

Temperture sending unit. Replace. Got it.

Check all vacuum lines and throttle body connections for leaks. k.

Scanner, eh? Where would I pick one of those bad boys up?

 

I have a scanner that is no longer made, but many people here have bought some and are happy with them. About $150 or so. Do a search.

It is extremely difficult (without proper testing equipemnt) to check the ICV for proper operation, However, when your engine is running rough, tap on the valve with the back of a screw driver and see if there is a change in idle. You can also remove the 2 screws and valve and spray the inside with carb cleaner and put it back on. All it is is a little verticle window that pivots open and closed based on how much air is needed to bypass the throttle body to keep the engine running. You can also temporarily increase the idle by putting a thin object between the throttle cable connector and plate. If the idle stabilizes, it may indicate a bad ICV. A new one is less than $150 and autozone carries them. Make sure your throttle body and intake are clean.

I would get the scanner, as it may showing you something obvious, such as an incorrect signal from the MAF. Even before getting the scanner, clean the MAF and see if improvement is noted. I would also run a few tanks of gas with some injector cleaner if you haven't done so already.

The 3.4 will idle rough at times, but seldom. It is normal for these cars to have the idle fluctuate +/- 40 rpm when warm.

 

Great, great info, 1999Porsche911! Thank you very much. I'll check into all of this and let you know how it goes.

 

Do you get a rough idle when you have the AC off? Try checking with the A/C on and off. I get a rough idle when I turn off the A/C. I believe that the A/C was designed to be on most of the time.