CIS Cold Start Warm up problem

[LFogelson]

I have an '82 SC. When I cold start it fires up immediately to 1200 RPM, after 15-30 secs the idle drops to 900 and is rough. If I try to drive the car it hesitates and backfires. If I wait 3-4 minutes the idle increases to 2000 RPM, the car runs great, and as it warms up completely the idle returns to 900 and the car has a solid steady idle.

I know I need a dwell meter, fuel pressure gauge, and CO meter to properly setup the CIS. However, the pattern is so predictable I was wondering if anyone else has had this problem? Is the AAV stuck open, closing after running for 3 min, and the slowly opening again? Or is one of my multiple throttle switches bad? The car seems to smoke more during the rough idle and the exhaust smells funny during the entire warmup - like a boat - too rich?

Is there a component I should start my testing on? I checked my timing. I have tried small adjustments in the CO mixture, nothing has helped yet. Incidently, I failed my emissions this year (CO too high) after getting the CO set by a wrench 1hr before. No problem with emissions before this present problem that all started after getting an intake manifold leak fixed. Thanks.

[bigchillcar]

my thoughts would center on the aav not opening...if not, the cold idle speed won't rise resulting in a slow, rough idle. there's a test you can do on it that involves putting it in your freezer for a while and then removing it to see if it closes and opens as it should.

also, backfires are often signs of lean mixtures...could be your percent co is on the lean side or you have a big vacuum leak...check for leaks with carb cleaner.

also could be the wur...if control pressure is too high, it will limit plunger movement in the fuel distributor and thus limit fuel delivery to the injectors...thus a lean condition.

probably not a leaking cold-start valve...this would cause an excessively rich mixture...you wouldn't expect a backfire with this condition.
ryan

[keithdog72]

be careful checking for vacuum leaks with carb cleaner. VERY FLAMMABLE. I have heard of many people starting fires this way. You can use water instead

[ischmitz]

Is the microswitch for idle engaging properly. A simple test is to open the throttle by hand in the engine bay ever so slightly with the engine not running. You should be able to hear the click when the switch disengages. If not your cold start enrichment does not work. You need to adjust the position of the switch.

The initial high idle is the fuel from the cold start valve injecting fuel during cranking. It gets used up real quick and then you run too lean (no cold start enrichment) causing your rough idle and backfire.

Ingo

[Carl_Boehme]

On a cold engine the Warm Up Regulator (WUR) is controlling the Control Pressure which controls the mixture. This is accomplished via the bimetallic strip and heating element within the WUR.

If the heating element is open (easily tested with an ohm meter) then the engine will start fine and then run rich until the WUR heats up (several minutes). The heating element prevents this from happening. Augmenting the heating of the bimetallic strip with the heating element causes an increase in Control Pressure and leaner mixture in a shorter time resulting in a smooth running engine.