'74 idle speed characteristics at start and upon warming-up?

[bigchillcar]

Hey folks,

Per my '74 manual, I always start my CIS car with the hand throttle in the 'all the way up' position. The car always starts strong on the first crank and subsequently idles between 1000-2000 rpm's in general until I lightly tap the throttle and then it usually moves to the upper range. Next I attempt to adjust the idle with the hand throttle to ~ 1000 rpm's by pushing the lever down about half way. As the car warms, I have to keep lowering it until finally it's all the way down and now idles ~ 800 rpm's. At this point, the temperature needle has begun to move some from 'dead cold' (I know...I should never use this word in the presence of my car! ) As the car reaches operating temperatures (180-220 depending upon season), the idle gradually moves upward to ~ 1200 rpm's.

This is typical operation for my car. Is that what I should expect to see? I read often where the idle should be ~ 950, but mine seems to vary like this with temperature. Were I to just push the hand throttle all the way down immediately after starting, the idle is usually only ~ 500...maybe even a little less...low enough that the alternator light will flicker as you'd expect and the radio will cut in and out. Does anyone concur with this behavior?

Ryan

[bigchillcar]

bump.

[bigchillcar]

awwww...can't somebody tell me how theirs does or they think it should idle when started and then when warm??

[bigchillcar]

cool! still no feedback!

[CamB]

The idle spec is for a fully warmed up engine. Your idle is a little too high.

Otherwise you have a perfectly functioning hand throttle (min doesn't, so I have to use the ball of my foot )

[bigchillcar]

Hi Cameron,

I think I've seen you on my threads before...thanks for replying. If I understand you correctly, the warm idle speed should be ~ 950 rpm's, but not necessarily the immediate starting rpm's...those are adjusted by means of the hand throttle. And I agree with you that mine is working properly...I'd hate to be developing a case of 'heel hocks'! I suppose a cable on yours is either broken or just too far out of adjustment?

Anyway, I have a feeling that my starting idle speed shouldn't be as low as < 500 rpm's. My car has been running a bit rough under load while still cold in the lower gears, but smooths out by the time you've winded second or into third. From what I've read, the WUR is the most likely culprit and would probably explain my very low cold idle speed. Would you tend to agree?

In all honesty, I need to check the condition of my airbox, points, cap, rotor, etc. to rule those out, but my car's symptoms seem to mirror more closely the with a clogged WUR.

See...I'm just trying to pull you in deeper!

Ryan

[CamB]

Hi

If only I could find a picture of someone holding their fore-finger and thumb about 1mm about.

Because unfortunately that is about how much I know about CIS!!!

The '74 and '75 cars are slightly unusual in that they have the hand throttle - in case you hadn't noticed all it does is pull the throttle pedal down by moving the rod! Mine doesn't work beause there is a nylon part in the hand throttle mechanism that probably fails in 100% of all early 911s (I suspect many people have ones replaced by the PO). They get extremely brittle with age - I can snap bits off the old one with light fingure pressure. But I am getting off-topic here.

What I am getting at is that I don't know how the startup function works on a '74, only that it is simplified compared to (say) a '76 or an SC. I just checked - still has a WUR though (no AAR???).

If your definition of running rough and mine are the same, I wouldn't worry too much about it (I would be happy if it was a bit "fussy" <2500rpm when cold but ok above that and ok when the needle starts to move). It is nearly 30 years old - what is your expectation?

[jk911]

I have a 1975 911 2.7 with the hand throttle and I experience a similar scenario, 500prm's seems a little low check the timing. But generally mine is the same. Its annoying if you are in a hurry to take off quickly in the morning ...

[bigchillcar]

Hey guys,

Yeah Cameron, I believe you're right...it has a WUR, but no AAR...probably because it has a hand throttle instead. The AAR is supposed to provide the 'air' side of the equation, essentially what the throttle does, as the the WUR is the fuel side. That's sorta my guess for why our cars have one, but not the other. Maybe Porsche figured too many people were confused by how to use a hand throttle or they thought it seemed kind of old fashioned.

Anyway, it sounds like a common problem. You guys are right...30 years is a long time for perfect expectations, but apparently there are those eventually working out these kind of driveability issues. I'm going to keep hacking away until I find out. Besides, what else would I be doing with my spare time and money?!

Ryan