Wow! What a difference adjusting the idle screw makes...

[R22tech]

After reading several posts about adjusting the idle screw air/fuel mix, I checked mine out just for fun. I never really noticed any problem w/ my idle other than it seemed a little low. Always pass the smog test w/ flying colors. But I went ahead and exp3erimented anyway. After a few trial and error adjustments my 85 Carrera has never run so well! Not only does it idle like a sewing machine, it "seems" like it is quicker and more responsive now. No more "flat" spots in the lower RPM range. Hell, it even shifts better. My point is: if you are driving an older 911 there are many NO-COST ways to improve perfromance. When I 1st got the car it wasn't too impressive as far as accelleration goes. A few weeks later, I noticed the accellerator cable by the air flow meter had "slack" in it. I adjusted the little black, plastic screw to take up the slack and the car showed a HUGE improvement in performance! Over time, these cars get a little out of adjustment. Makes sure your 911 is running properly BEFORE spending all your money on performance upgrades.
I wonder what else needs to be adjusted.....

[adamnitti]

so, r22, what did you do to get it right?

p.s. thanks again for noticing and fixing the slack in my accel cable. the car runs and SHIFTS better!!!!!

------------------
Adam Nitti
ajnitti@mindspring.com
www.adamnitti.com
'85 911 Carrera Coupe
'72 BMW 2002tii
'97 Grand Cherokee Limited
Peachstate PCA member

[ChrisBennet]

Originally posted by R22tech:
A few weeks later, I noticed the accellerator cable by the air flow meter had "slack" in it. I adjusted the little black, plastic screw to take up the slack and the car showed a HUGE improvement in performance!

Sorry R22Tech I forgot what kind of car you have. Could you be more specific on the location of that little black plastic screw?
thanks

[Superman]

I feel a little vindicated here. I am always telling folks to tune the engine and do the maintenance/adjustments before assuming that expensive parts are failing. Here's a story:

Woman complains to her mechanic (it might as well have been a man) that her car just does not have as much power as it used to. Mechanic opens the driver door, reaches down and pulls the rug back so it is no longer interfering with the acelerator pedal. You see, the rug was not allowing the gas pedal to open the throttle past 2/3. A loose throttle cable would have this same effect.

I personally have found that installing a weaker throttle return spring makes people feel that their car now has more power. Most motorists would notice the difference if they changed their distributor cap and rotor.

------------------
'83 SC

[R22tech]

Chris, it's an 85 3.2. The black, plastic adjsutment screw is located to the left of the airflow meter. Just find the accel. cable and you will follow it to the screw. Adjusting it was like adjusting the brake cable on the handbrake of a bicycle-just turn it by hand to take the slack out of the cable.
Adam-I basically just started turning the idle screw counter-clockwise and used my ears to listen to the idle and my eyes on the tach until it sounded smooth at approx. 850RPM. Test drove and the idle was "bouncing" for a moment when the clutch was depressed so I adjusted a small amount CLOCKWISE and re-tested until I had a smooth idle and a smooth delivery up the RPM range. It took a few times to get evrything to come together-total time:20 minutes. Helpful hint: do this with the engine at operating temp.

[john walker's workshop]

i'm just wondering what black plastic screw you mean. the only one i can think of is the adjuster for the cruise cable. the mixture screw is accessed by an allen wrench inserted into a hole in the airflow meter. the speed screw is the brass adjuster directly in the center/rear of the throttle housing, originally covered with a yellow plastic cap that needs to be broken off to do the adjustment.

[DJB]

Interesting post!

I too was wondering about the 'black screw'. The manual suggests that the base idle screw (covered with the cap John suggested) should not be tweaked for idle speed.

My question is that my CO levels are perfect, but my idle is only 650 - 700 RPM, what do I adjust to increase this to 850 RPM.

Thanks


------------------
David
86 Wide Body Cab
Sydney, Australia

[john walker's workshop]

the idle speed is set by the factory and will never need to be adjusted. HAHAHA. turn the screw counterclockwise with a 7mm deep socket to raise the idle, after removing the yellow plastic cap. do it with the engine hot and drive it afterwards to be sure it stays where you put it.

[Decolliber]

I too was intrigued by the reference to a black plastic accellerator cable adjustment nut. In my 88 Carrera there is no accel "cable", only solid metal rods, and I do not see any adjustment point.

[R22tech]

O.k. let me clarify: I adjusted the brass 7mm screw to set my idle speed. It had no cap on it and was facing me at the air flow meter.

The black accel. cable screw is to the left of the brass screw . It is plastic and, what I believe is the accel. cable end, goes through this screw. If i turn it counter clockwise it tightens up the cable and if I go too far it acts like I'm pressing the acclerator down. Just look at the throttle return spring, you know, where you can rev the engine from the engine compartment if you rotate it by hand; the cable is right there! If it looks like has slack in it, meaning, the end of the cable has to move 1/4" or more before it moves the throttle, then this plastic screw can be adjusted to take up that 1/4".

This seems trivial to me, but maybe I just don't know the correct terminology! I will look at it closely when I get home so I can make my description more accurate.

[This message has been edited by R22tech (edited 10-10-2001).]

[This message has been edited by R22tech (edited 10-10-2001).]

[R22tech]

also-I did not adjust anything that required an allen wrench. I believe all I did was adjust the idle speed and took up the slack on the accel. cable so when I put my foot on the gas-it responds without hesitation. I assume that before this adjustment to the cable, when I floored it, I wasn't ACTUALLY at full throttle. The car is definetely faster now. I did the same cable adjsutment on Adam Nitti's 85 Carrera and he experienced the same results I believe. Maybe he can shed some light on my description. Adam?

[R22tech]

http://www.nosubstitute.org/events/LAConcours3June01/DSCN0045.jpg


I don't know how to circle the items in question but: look at the picture: find the cable located at the top, left of the yellow sticker that has the refrigerant charge listed on it. Now follow that cable to the right and you will see the black, plastic screw housed in a square, brass clip. That is the screw that can be adjusted by hand to take up the slack in the accel. cable. The idle screw in this pic. HAS the yellow cap on it and is in the center of the pic and up about an inch from the top of the fan.

[This message has been edited by R22tech (edited 10-10-2001).]

[Decolliber]

I think the cable to which you refer is the cruise control cable. I am not sure how adjusting that screw could affect anything other than setting the speed on cruise control (i.e., if the cable is slack, you wont get the speed held at where it was when you turned on the cruise control).

[R22tech]

Decolliber: I'm not sure I agree w/ that. The cable may be coming from the cruise control unit, but it is attached to the accelerator pedal ultimately. When you set the cruise control, doesn't your accel. pedal move up and down to keep it at speed? All I can tell you is that I'm no expert, but, there is a definite difference in pedal response when adjusting this cable. After reading your post I went out and double checked by turning that screw clockwise and adding "slack" to the cable. The result was DECREASED pedal response and lower performance. Check it out yourself, let me know what you find.

[orbmedia]

Sometimes I do tech inspections at DE and club races. I have noticed the majority of 3.2 Carreras have slack in the accelerator cable. I'm wondering if it's there by design.

[Decolliber]

Originally posted by R22tech:
Decolliber: I'm not sure I agree w/ that. The cable may be coming from the cruise control unit, but it is attached to the accelerator pedal ultimately. When you set the cruise control, doesn't your accel. pedal move up and down to keep it at speed? All I can tell you is that I'm no expert, but, there is a definite difference in pedal response when adjusting this cable. After reading your post I went out and double checked by turning that screw clockwise and adding "slack" to the cable. The result was DECREASED pedal response and lower performance. Check it out yourself, let me know what you find.

My cruise control cable has been cut (by PO?) about two inches short of the throttle arm so I cannot do any fiddling there. Maybe I should get a new cable and experiment.

[Ted Stringer]

The peddle on the DME cars has a pull rod in the tunnel which connects to a pivot that mounts on the transmission. This connects to another rod that runs up to the throttle body. I think that you can see the pivot on the side of the transmission with the car on the ground, but next time you have the back up on stands have someone press on the gas while you watch under the car.

There is a area in the rod that attaches to the throttle body that allows the cruse control to pull on the throttle and not have to move the peddle assembly.

------------------
Ted Stringer
nuke3@juno.com
'84 911 Targa aka pocketrocket

[jsmarcus]

No cable on my 84, just a rod. I was very interested in trying but as my car does not have cruise control, no cable. I've never noticed any pedal lag, though. I will try to change the idle speed a bit, though.

------------------
Josh
Black on Black '84 Carrera

[R22tech]

After further investigation this is what I think goes on when adjsuting the black plastic screw. I now agree this cable is NOT the accel. cable and is , in fact, the cable for the cruise control. So how does it make the accel. pedal more responsive? I believe when you adjust the screw and take up the slack, it causes the throttle to move as well and so the accel. pedal does not have to be pushed as far to operate the throttle. In other words, this cable is , in essence, a 2nd accel. cable that is operated by the cruise control unit. Either way, it effects the throttle the same way tightening up a loose accel. cable would, and therefore throttle response is improved. What do ya think?

[KTL]

If you tighten up the cruise cable, you are effectively pulling on the throttle body linkage and partially opening the throttle. I think this is where you are getting what appears to be increased throttle response.

The cruise cable "holds" the throttle open at the position you set when the cruise is activated. I believe the cruise control unit tries to maintain the same amount of vaccuum as the car goes up and down grade changes in the roadway. The attempt to maintain the same amount of vaccuum is done by varying the throttle position.

The cable doesn't affect throttle actuation. Mine was broken when I bought the car and the throttle worked fine. As stated earlier, the throttle is opened/closed by rods from the pedal thru the center tunnel to a link just outside the underbody of the car. The link is connected to a bell crank mounted on the side of the trans. case. A rod with a looped end and crescent bend along its length (to go over the CV axle) comes off the bell crank and is connected to another bell crank (double-sprung) underneath the intake manifold. There is then one more "bent" rod from the double-sprung bell crank to the throttle body linkage. That's how the pedal moves the car (assuming your engine works).

------------------
Kevin
87 Carrera coupe

[This message has been edited by KTL (edited 10-11-2001).]