74 911 idle problems
 

Please understand that I am very amateur when it comes to engine repair, and am trying to learn as I go. Here goes:

When I start my 74 911 (CIS) it stutters a bit and also stalls if I take my foot completely off of the gas (warm or cold). It's a sportomatic and I can get it into gear if I leave my foot on the gas for very low revs, but when I drive, the revs drop and car stutters before accelerating.

I'm hoping it's not a huge fuel injection issue, and I'm hoping someone may be able to help. Is this maybe some sort of air leak?

Obviously, it's hard to diagnose with a keyboard but you should start by looking for a vacuum leak. Hoses get old and brittle.

Look around the engine compartment with a light and see if you can see anything obvious.

If all looks ok, start the car, leave it in neutral with the park brake on and see if you can hear anything that sounds like like an air leak or even a whistle.

Do a search for your problem on this forum if you don't find a vacuum leak. With a CIS system, it could be one or more components that need attention. Depending on your mechanical skill you may need to get some help from a Porsche tech or maybe even a fellow Pelican that can look at it in person.

Your symptom is one indication of an out of spec warmup regulator (WUR) which controls the fuel mixture throughout the entire operating range of the engine; not just during warmup. It is very common for these units to gradually go out of spec until the mixture becomes too lean for proper starts and operation.

As Wayne said, check for vac leaks. They are very common in old hoses and components, and can cause the same lean condition.

If you separately search the WUR, vacuum leaks, and CIS start and run problems, you will find a lot of info on this.

If you feel up to it, you can use a CIS fuel pressure gauge that can measure your fuel and control pressures, and determine if it is the WUR. An air/fuel meter can also determine if your mixture is set correctly.

There are procedures you can find here via a search for testing the pressures, the operation of the other fuel injection components, and how to check for vac leaks.

Check out jim williams' website on rennlist for CIS info. He also posts here. There are a;lso some videos posted by ricks911s on testing fuel pressures.

If this is not something you want to do, a competent shop w/ CIS experience should be able to do these tests for you to help the diagnosis.

I have almost no knowledge re the sportomatic, so I can't even speculate if there is something wrong there.

Good luck, and let us know how you make out. And don't forget to post some pics of your car.

Class act response. This is the type of member support that makes this board a great place for fun, quality information and solutions.

Not to oversimplify, but is your throttle hand lever working properly? You can use that to increase the idle untoil your engine warms up.

Genius is many times simplicity. This should have been the 1str question asked as symptoms reflect non utilization of throttle hand not engaged or hand lever piece needs to be replaced. I just replaced mine.

Good one, fintstone and AshEvan. Porsche deleted the hand throttle for MY 1976.

Thanks for the compliment AshEvan.

As w/ all CIS cars, you should first make sure all ignition components, incl points, plugs, cap, rotor and wires, are operating correctly.

I have the awesome auto climate control in my SC so the throttle lever thingy isn't something I think about.

Thanks all for the suggestions. I've messed with the hand lever and it doesn't seem to make any difference if it's up or down.

I'm gonna go look at it some more, do some web surfing, and make a call or two. Hopefully I can figure something out by the weekend so I can make it to "Porsches and Pints."

When you pull the hand throttle up does your gas peddle depress? If this is not happening, this could be one cause of your problem.

There is a plastic piece that sits on the base of the hand throttle that engages an adjustable spacer that sits on the accelerator cable. When the hand throttle is pulled up, the plastic piece pushes on this spacer which moves the cable and in turn depresses the gas peddle. The mechanism sets a cold start throttle in the engine which was put in place so that owners wouldn't blow up their air boxes when the car was cold.

If your accelerator pedal is not depressed at all when you pull the lever up, the plastic piece could be broken. If it is only gets depressed a little, it could just be a matter of adjusting the spacer which you can get to via the little hole that sits just in front of the brake/throttle/heater cluster under the carpet. There are some really good posts here on how to replace and adjust this piece which is what I referred to in fixing mine.

Good Luck

Here's an update:

It was running too rich. The fuel distributor apparently jammed and the reason is that the gas tank is full of rust (hooray!). From what I can gather by searching this site, this has happened to other people. I'm thinking of just replacing the tank, as it seems to me that repairing it (by having it cleaned professionally) wouln't be that much more inexpensive. Not to mention the fuel distributor repair still needs to be done...