CIS cold idle speed question

Since CIS idiosyncrasies have been a favourite topic lately, I'd like to add my own symptoms- maybe someone else is/ has experienced the same:

I believe I have a vacuum leak somewhere in the CIS system, as the idle tends to hunt up & down slightly (~850 - 900rpm) in a rythmic fashion. However when started from cold this surging is much more pronounced for the first minute or so (the idle varies from ~500 - 800rpm). I understand the CIS system is designed for a high cold idle (1200-1500rpm?) for the first couple of minutes, something mine doesn't do. The car fires up just fine, but the idle speed is too low, gradually increasing as the engine warms up. Is it likely these symptoms are all caused by vacuum leakage, or could there be something else at fault, cold start valve, AAV?

Andrew

[scarebus]

Andrew,
Seems like your cold start valve is not working. Remove the electrical plug off the cold start valve.
1. with engine cold, put multimeter(DC) on plug
connectors. Start engine to see there is 12V.
or
2. remove cold start valve. make 2 jumper wires
so that you can hook up to the pins on CSV.
Connect one lead to positive terminal of a
battery, and the other lead, just touch the
negative terminal of the battery. If the CSV
makes a klick when you complete the circuit,
the CSV is good. Make sure the fuel discharge
hole is not covered close with soot.
By doing the above tests, you can tell if its the
CSV or the wiring, etc.
Good luck.

[bigchillcar]

Andrew,
Aquick check if you have a vacuum leak: spray carb cleaner inyour engine compartment around the air box, hoses, etc. If the idle speed jumps up, you've got a vacuum leak.
Ryan

[wckrause]

Surging and hunting is a symptom of a too rich mixture. Vacuum leaks cause a lean mixture. During cold start, the mixture is enrichened, so that may explain your symptoms getting worse during cold start. You should work on getting your mixture set properly first.

CIS questions always seem to become more frequent as the weather gets colder.

I've been meaning to get the mixture checked. I had actually been wondering if it was running a bit lean, as it passed CA smog with flying colors. The O2 sensor is still connected, but I still wonder if its a little strange it should pass so easily? I'll be changing plugs this weekend, so that might give me a clue. I'll see if I can check the cold start valve as well.

[Sunroof]

I had the same problem, but I do not have the extra gismos on then new CIS cars. Mine is the great 1973.5T CIS experiment!!

My idle on cold start acted like yours so I purchased a t-handled hex adjustment tool and began to tweek here and there until it improved. Its been perfect ever since. You do not need a CO meter to get it right. To richen go right (clockwise) one small click at a time.

Interestingly, my mechanic installed a new WUR thinking that was the big issue because he was turning the mixture screw and nothing was happening. Well, one time I took off the air filter housing and decided to hold the sensor plate while I tried to adjust the mixture screw. It was every hard to adjust, BECAUSE someone put locktite on the damn thing!!!! After some PB Blaster and turning it back and up, I finally loosened it up enough to set it. All this time my mechanic thought he was adjusting it!!!

Just a word of caution if the screw fails to turn (click at a time).
Try checking the mixture as well as the cold start valve and see if that helps.

Regards
Bob
73.5T

[Hladun]

1. The cold start valve has nothing to do with idle speed unless it leaks. It only functions while the starter is engaged! And the thermotime switch must be correctly connected or it doesn’t do anything at all.
2. The AAR controls cold idle speed. The port should be partially open when the engine is cold and fully closed when the engine is hot. Cold engine idle speed should be around 1,500 rpm.
3. The surging is a cold engine CIS characteristic that never goes away completely. However if it is several hundred rpm in range then remove the AAV (this also stops startup backfires), make sure the deceleration valve is properly set (warm engine takes a few seconds to return to idle when the throttle is quickly closed) and make sure the richness is correctly set.
4. WUR’s are expensive, easy things to replace that are probably not broken. Get the JC Whitney CIS pressure tester before you spend the money on a new WUR.

[bigchillcar]

CIS questions always seem to become more frequent as the weather gets colder.

Yep, Bill beat me to it...I was just about to post a thread of the same observation.
Ryan