Hey guys...'86 911 (stock)


Went out for a spin with the wifey yesterday and noticed that the car had an ever so slight rough idle on the cold start. Didn't notice anything while on the 50 mile drive. Then we got back home and noticed an ever-so-slight rough idle AND whining. My wife said it sounded more like air/vaccum than engine whine.....and I would have to agree.

Before I go hunting the archives, is it most likely these (rough idle/whine(whistle?)) are inter-related or is it just coincidence. I intend to look in the engine bay for anything obvious, but thought with the onset of these at same time perhaps menas something 'very' specific. Idle does seem to be a bit low....650 rpm or bit more.

TIA

Edit:
One quick note....went out to the car and felt the fan belt....very loose, as in I could very easily move the fan while the belt stayed in place.

 

That is very low, should be around 900 or so. When I start my car in the cold "weather", she will hunt up and down for a few seconds, but then corrects itself. Something seems wrong.....

 

Check your Idle Control Valve. It makes a slight buzz and will cause the engine to idle low if it is not fully opening.

 

check the above, as well as vacuum hose connections at the back of the throttle body.

loosen the spark plug wire holders, and remove the distributor cap. Check rotor shaft for play. If the bushings are going, then they'll whine. And you'll have a few more hundred miles before they go.

 

You say whine, but then you reference the air noise and use the word whistle. I'd not mix those two sounds in my head. But, if I focus on whistle or air noises, I'd look at vacuum, which would also explain a low idle. Check the throttle body, and elbow and connections (hose clamps) and the clamps and hoses off the ICV, as well as those mentioned by rusnak, and the breather hose connections on the RH of the compartment above the oil fill. Those are probably the low hanging fruit. Next would be the intake legs, which is a little tougher.

With the engine running, you can spray starting fluid at any suspect area, if the RPM's rise when you do this, that pretty much confirms an air leak at that point.

 

Thanks guys.....having been lucky to work with some of the best minds (George Soros, Julian Robertson, Stanley Druckenmiller) etc in the Hedge fund world for 20 years I am equally honered to be part of this group and eager to learn from you.

Amber/Rusnak/Ed.....thanks, I will head in that direction as time permits.

I did tighten the fan belt (had 6 shims in back and thru 2 up front, now 1/4 to 3/8" tension).....the crazy thing is I was just looking through the engine area (first time really) and found middle plug on passenger side loose !!! Snapped it in so its now tight.....sheesh, now I see why you guys are meticulous with your efforts.

 

Just as an aside, my 89 had always idled quite stabily over all season, for many years. She never really exhibited the higher idle spec for this year but was relatively close (per RPM gauge). I often noticed how a nice tune-up (fresh plugs, distributor cap, rotor button, air filter, lube AFM, remove/clean ICV) always HELPED with a nice steady idle. Dig,..then, I'll change these parts a bit more often than normal (which I do).

One day, I was bound and determined to check my base idle and attempt the goal of 880 RPMs. Although I got the idle up a bit, she started to (occassionally) exhibit idle hunting upon startup,..never after she was warm......sometimes it would take (winters) up to 30 seconds for her to regain idle control to steady state. I was certain to NOT touch the idle mix screw (duh?) during any of this procedure.....she seems to have recovered over the past few months, as temps are getting warmer.

I feel like I need to get the idle mixture checked (set?). I've been told that the idle speed adjustment will not impact the mix setting,..true?

Otherwise,..on to suspected vacuum leaks...very, very intermittent , at that. Nothing raising it's head presently...when we had the engine down last, all vacuum lines were changed to new stuff (few years back).

Guess it's time to spray some "you know what" around some key areas and see what shakes.....

Some of the (specific) noise could be belt-related,..so do set that tension properly (and NOT TOO DAMNED TIGHT)
As well, that ICV could use a cleaning..........as to idle,...not to mention checking the idle switch.

For now she (mine) runs like a raped-ape....but am interested in getting the mix verified. Maybe go price some test devices (LM's).

Best of luck!

Doyle

 

The elbow hose off my ICV had hardened. One clamp would not seal it well. IIRC, I ended up double clamping to get a good seal. I'd douse your ICV with some spray silicone, it may hang up when it's cold.

 

try to pinpoint where the sound is coming from. A mechanic's stethescope, or a long prybar handle end pressed against the ear can go a long way to diagnosing what's wrong.

 

Could it be a bad O2 sensor causing the car to hunt at idle?

 

Yea....while I was searching, that did seem to come up often. The odd thing is that the idle hunt and whining/whistling came on at same time. Ed did say he would not use whine/whistle together. My wife said more whistle. Will start with vaccum leak search.

 

did the whine continue after your wife got out ?

sorry .. i couldnt resist ..

 

hum....now that you mention it

 

well,..either the description (whistle/whine,..I see these as COMPLETELY different animals-but then I'm into audio.....) is correct or not........

,,...and theiceman will continue to provide quality humor (seriously,..he's Canadian!)

Best!

Doyle

 

not to hijack at all but Doyle did you hear when the new Rush album is coming out .. this is a seriously ridiculous long time.