CIS / Hand Throttle Question

[gjp1960]

Lately my 1973.5 has been idling irregularly when fully warmed up with the hand throttle in the full down position. Kind of a rhythmic up-down thing, where the red light will flicker a bit as the rpms dip. My temporary fix to avoid stalling out in traffic has been to engage the hand throttle just enough to keep it idling smoothly at 1000 rpms.

I guess I have two questions:

1) Does this hurt anything in the long run? I understand that pulling up the hand throttle activates some kind of microswitch that enriches the fuel mixture. Does it only do this when you pull it all the way up?

2) I would like to learn to tune up the CIS system myself. Can anyone recommend a good source of information to learn about it before I get in there and mess with it?

Actually, that's 3 questions. Thanks!

Greg

[IROC]

I think the hand throttle merely mechanically pushes the gas pedal down slightly. I don't know of any microswitch that is activated. I have a 3.2 in my car and the hand throttle raises the idle speed on that, too...

Mike

[gjp1960]

Thanks for the reply.

Anybody else familiar with the hand throttle on a 73.5 CIS or where I can learn to work on it?

[dougcl]

Greg, sounds like you are running too rich. Have you done anything to the car recently? It may be a simple as getting the mixture set.

Using the hand throttle is the same as pressing on the gas pedal. You should be able to feel the gas pedal move when you move the hand throttle.

There are several good books on CIS. I've used the one by Charles Probst. Look it up on Amazon.

Doug
75 911S

[hbf]

The microswitch is there to activate the cold start injector. However, the switch is in circuit with the starter motor so both the starter motor has to be cranking and the microswitch closed to activate the cold start injector.

The switch is in the accelerator cable circuit so it turns on and off all the time as you use the foot pedal but only does something at start up and only then if the accelerator or hand throttle is activated.

No damage can be done to anything by using the hand throttle.

I have a soft copy (pdf format) of the booklet published by Bosch on their CIS K-Jetronic fuel injection system. I will let you have a copy if you like. Please let me have your e-mail address.

[Jump2xs]

First a disclaimer: I am a total neophyte when it comes to fuel injection, but let me share some info I picked up from a book I bought from our sponsor titled "Solving Bosch CIS problems" By James Weber. http://www.pelicanparts.com/catalog/shopcart/911E/por_911E_documt_main.htm

This book addresses your symptom by giving the possibility of a worn component of the air intake sensor plate---some kind of small pivot wheel that can get worn out and cause the idle rythym you describe.

This book is not an official Bosch publication, nor is it Porsche specific, but it seems to cover our components thoroughly. It is written in a no nonsense, easy to understand manner. It's filled with lot's of inside tips and recomendations. I bought it to help me understand and do repairs on my latest love.

The big down side to this book is the price, 42+ bucks, and the trouble shooting table is somewhat useless because there is no weight put on the various possibilities---so where do you start?
Hope this info helps and Good Luck

[Gunter]

A hand throttle is just there to mechanicaly open the throttle, the same as the gas pedal. You may have to go through the steps of a tune-up. Points, Timing, Mixture, etc.

[dougcl]

Greg, Jump,
Oscillation in the idle is common and usually indicates a rich condition. Chances are the problem will be solved with the turn of a 3mm allen wrench.

Doug
75 911S

[Jim Sims]

"A hand throttle is just there to mechanicaly open the throttle, the same as the gas pedal. You may have to go through the steps of a tune-up. Points, Timing, Mixture, etc."

The above is not correct on a 73.5T with CIS; the hand throttle when pulled all the way up activates the cold start injector circuit (via a microswitch on the throttle body) but only while the starter is turning. Starting may be difficult if the the hand throttle is not pulled up.

Cheers, Jim Sims

[bigchillcar]

The above is not correct on a 73.5T with CIS; the hand throttle when pulled all the way up activates the cold start injector circuit (via a microswitch on the throttle body) but only while the starter is turning. Starting may be difficult if the the hand throttle is not pulled up.

Jim, are you sure about this information? I've replaced the hand throttle as well as the plastic lever connected to it that fits on the accelerator cable in the tunnel. The plastic lever butts up against a metal stop to allow the hand throttle leverage in pushing the cable where one can see the accelerator pedal being physically moved down (performing the same action a little foot pressure would do). I believe that by simply turning the key to run activates the thermotime switch which detects block temperature. If temp is below ~ 90 degrees, the cold start valve is activated. If it's above, it isn't in the start sequence. However, I agree that failure to use full hand throttle per the manual will make for difficult starting, unless of course the engine is already very warm.
What am I missing?
Ryan

[Jim Sims]

Yes, I'm sure about the 1973.5T CIS; I just rewired one yesterday. The 73.5 T's do not have a thermal time switch. The circuit passes through the starter, then to the microswitch and then to the cold start valve. I believe the thermal time switch is used in the circuit in 1974 but I'm not sure if the microswitch is still there in 1974. Jim

[Jim Sims]

1974 CIS cars had a microswitch in the cold start circuit.

911 73T CIS issues

Cheers, Jim

[gjp1960]

Thanks to all for your help. This is an excellent forum and I am learning much.

[bigchillcar]

Jim,
Thanks for the link; great post. I didn't realize the microswitch was in the circuit, thought the thermotime simply sensed temperature when power was supplied by the battery and based upon temo, operated the cold start valve or not. Thanks for the rest of the story!
Ryan

[47silver]

hi
if nothing has changed in the engine, i would suggest that you adjust the points first. i had tons of idle problems and had a bad set of points. i replaced them with a pertronix (from pp) and the engines idles perfectly.

gary

[Sunroof]

Do not dispair fellow 73.5 owner.........

I had the same symptoms and the car would even die after coming to a stop. What you need to do first is check your points for the proper gap then adjust your mixture properly. You will need the 3mm allen wrench for the adjustment. Its best to use a CO meter, but you can play around cautiously with 1/4 clicks at a time. To the right (clockwise is-rich)....to the left (counter clockwise is lean). Too rich of a mixture will creat a fluctuation as you describe........a word of caution.......several mechanics claimed they tried to adjust my mixture and it cost me in the long run a new cold start valve, warm up regulator and air box with new runners, pop-off valve, etc........in the end all the trouble was simply someone placed locktite on the adjustment screw and it was not turning!!!!!!! I had to pick the crude out with a dental pic myself in order to adjust it properly...talk about a major fluke?

Give that a try and see what happens....

Bob
73.5T