Idle question

[jshape]

At start-up overnight (or when the engine is cold) my 79 SC idles at about 2100 RPM. While driving it the first couple of miles, the idle drops down to 950 RPM or so - right where it should be.

I'm hesitant to fool around with the idle adjustment since it runs so well after warming up and idles right where it should.

Will the higher idle at start-up cause issues? Is this something that is easily fixed? It doesn't really bother me to deal with the issue, but I don't want to ignore it if it could lead to more issues down the road.

Any advice would be appreciated. Thanks again to all of you for your participation on this board - it's truly an invaluable resource!

[Paulporsche]

A search will reveal that this is exactly how the CIS should work in these cars. Most threads are about owners who cannot get their cars to idle higher @ cold startup.

Now, having made that blanket statement based on what you wrote, does the time the revs stay high vary at all with the ambient temperature? Does it vary based on the type of driving you are doing? Do the revs gradually go down from stop to stop, or are they consistently @ 2100 and then suddenly @ 950?

[rs6er]

Originally posted by Paulporsche
A search will reveal that this is exactly how the CIS should work in these cars. Most threads are about owners who cannot get their cars to idle higher @ cold startup.

Now, having made that blanket statement based on what you wrote, does the time the revs stay high vary at all with the ambient temperature? Does it vary based on the type of driving you are doing? Do the revs gradually go down from stop to stop, or are they consistently @ 2100 and then suddenly @ 950?

Allow me to get in on this. My 81 SC jumps to 2100 when cold (hot or warm weather) Eventually it drops down, but sometimes not for a long time. My mechanic told me I need to replace a part that is not working properly, but at the time, I was already spending too much money on the rest of the work. What is the part, how expensive is it, and how hard is it to change it myself?

[Paulporsche]

The Auxiliary Air Regulator (AAR) is the component that puts the revs up and gradually lowers them down to warm idle speed as the engine warms up. Over time, these can get stuck, have their electrical connections get loose or broken, or have their internal resistance core go out of spec. If you search the AAR you will see lots of threads on this. Mystery train did a comprehensive thread that showed how he was able to vary the time the revs stayed high by reworking the internals. I think RarlyL8 also had a thread on his AAR. There are also tests to do to see if it is working correctly.

Keep in mind that the amount of time the revs stay up should vary depending on the ambient temp and the engine temp.

Other items can cause a high idle, incl a vacuum leak, a bad decel valve, a too lean mixture, and an improperly functioning distributor, but the AAR is where I would start in this instance.

I don't know if rebuilt or new AARs are available or what they would cost.

[rs6er]

It is the AAR that is the problem. Where is it located on the motor, and do I have to remove anything to find it?

[Joe Bob]

2100 is too high. Warm up regulator may be an issue.

[rs6er]

Originally posted by mikez
2100 is too high. Warm up regulator may be an issue.

Replaced

[rs6er]

Found the AAR. Do you have to take it off to clean it or do you just spray carb cleaner into it?

[Joe Bob]

Originally posted by rs6er
Replaced

Do you have a Bentley manual? Just because it was replaced doesn't mean it's working or adjusted correctly.

When I had a 3.0/CIS in my ride there were some issues on high idle....it was a combo of a few factors.

Best to check all the obvious and eliminate them. Have you checked for intake leaks?

[rs6er]

I have a very good mechanic who told me that this was the problem. At the time I didn't want to pay for a new AAR which is very expensive and he had done a lot of work. Now I am trying to figure out how to repair the one I have.

[Gunter]

rs6er: Do a search. Lots of info on how to check the AAR. You can take it off, or check it in place. Carefull with the electric plug, a small, small screwdriver for the wire-clip, and patience, will disconnect it.
All SC-years have the same AAR.