Why does it take a few miles to settle at a normal idle?

[Hotwatermusic]

'83 SC motor in a 74 chassis. New fuel injectors, spark plugs, and rotor. No 02 sensor. If left to idle at start up, the car first goes through a normal warm up procedure at ~1500 RPM, but then settles really, really low at ~400 RPM until it's been driven for a couple miles. Then it settles at a rock solid 950 RPM, as it should. Any ideas what's going on? It didn't always do this, so something has to be off--just don't know what it is! Thanks!

[scotricker]

After going through all the CIS obvious vacuum leak parts, my 78 3.0 still is a little unstable at idle when cold. But like yours, after a few miles, it's awesome perfect 950. Maybe your is just fine, too! I think they just run better warmed up.

[gsxrken]

Does your car have the auxiliary air valve? It opens a disc with a bimetallic spring like an old choke and closes when it gets hot. Search for how to test it in the freezer and oven (assuming your year even has one).

[Paulporsche]

As always, after making sure all your ignition components are in order, you need to verify the operation of your WUR and check for vacuum leaks and your mixture.

At first glance it sounds like your WUR may not be warming up correctly to match the needs of your engine. Or it's possible your mixture may simply be off. The AAR is another possibility.

My engine has no O2 sensor either, so it's critical to get that mixture as correct as possible to be the best compromise for all temperature conditions in which you drive since you have nor Lambda system to help control the mixture.

I have found that a too rich mixture will often aid in cold starting but will produce a too low idle during warmup. This can be caused by the CO setting or by a WUR that has its cold control pressure set too low for the ambient temp. This could produce your symptoms since the mixture is overly rich during that part of the cycle, but is then OK when warmed up and control pressures rise.

During this warmup phase are you able to raise the revs via the air bypass screw?

[al lkosmal]

Originally Posted by gsxrken

Does your car have the auxiliary air valve? It opens a disc with a bimetallic spring like an old choke and closes when it gets hot. Search for how to test it in the freezer and oven (assuming your year even has one).

+1 on the AAR valve. Make sure that it is plugged in and getting power....and, per above, that the bimetallic spring and disc still work.

Note: This unit is located between intake runners on the 4,5,6 side of the engine.

[kyle242gt]

Mine surges from 800-1500 for thirty seconds or so; I've imagined several times that's normal and, in fact, sign of a healthy CIS.

[Paulporsche]

Kyle,

Where have you read that?

I don't think I've ever come across that statement.

A surging idle is another symptom of a too rich mixture. On balance I think I'd rather have a too rich than a too lean mixture, but I'd rather have a correct one than either of the other 2.

[kyle242gt]

Hi Paul-
I've read that here multiple times, from seemingly well-respected posters... can't find the posts right now, but I lurk and read just about every thread that comes along in a sort of mental stockpiling for the possibility of CIS malfunction on my 80.

[boyt911sc]

Originally Posted by kyle242gt

Mine surges from 800-1500 for thirty seconds or so; I've read several times that's normal and, in fact, sign of a healthy CIS.

Kyle,

Where did you get this information? How many CIS car/engines have you seen or know that behave like this? If this is a sign of healthy CIS, all the things I have learned so far about CIS is worth nothing!!!! I don't think I could make my engines' RPM oscillate like yours.

This is probably the wierdest description of a good running CIS engine I ever heard. You learn new things every day and I got to find this critical bulletin soon. Thanks for the tip.

Tony

[Ramathorn]

Hahaha funny this popped up i was thinking the same exact thing this morning.

[kyle242gt]

Originally Posted by boyt911sc

Kyle, Where did you get this information?

Like I said above, I recall reading that here, a week or two ago most recently. Hopefully not spreading misinformation, just trying to chime in.... extensive searching in hopes of redemption have failed, so I will just retract my comment.

My 80, after sitting for a week or so, surged for all of 15 seconds before settling down this AM.

[Scott R]

The warmup surging is a funny problem. You have a temperature switch on the passenger side chain box cover that trips at 50deg c. One that switch closes the "computer" is now in closed loop.

So here is why I mention this... All three things, the WUR, the AAR, and the Lambda computer need to be in sync. If any of these items works out of time you get the surging or the low idle conditions.

The way to stop this on the cheap is to have a way to ground the CIS temperature switch until everything is warmed up. Or to have an O2 bypass switch until everything is warmed up. You can test this of course by ground the temp switch sometime.

I mention the above options because getting all of these items to work in harmony after 30 years of operation is very difficult.

[timmy2]

I'll stick my neck out fir you Kyle. I've read those statements in threads before, but I believe they were in reference to Motronic/Lambda or later style electronic and computer controlled cars. Not about k-jetronic.