My Erratic CIS Cold Idle

[BradH]

My cold idle has become increasingly erratic with changes in ambient temperature. Warmer weather (>55F), it wants to idle around 700 rpm, cooler weather (<55F), between 1200 and 1800 rpm. Oftentimes when the engine is cold, and the ambient temperature is cold, it will start out idling around 1100 rpm and then advance as the car sits to nearly 2000 rpm. All these symptoms go away once the oil temp needle moves past the bottom "thick" hash mark (sorry, I don't have a labeled gauge.) It is rock solid at 950 rpm once it has warmed up.

Here's what I've done in the past two months -- rebuilt distributor and set timing and warm idle (verified by prof. tech), had mixture and CO set to pass emissions and reset to about 2.5%, plugged line for decel valve as it was causing a hanging idle. The O2 sensor is unplugged.

Where should I start? Cold start valve? Fuel pressure?

Cheers,

Brad
'83 SC Coupe

[WB3]

Hi Brad, I know your posting is a bit dated but I came across it and seen that nobody replied...bummer. I'm having problems with my CIS system as well although not exactly like yours. But I do recall something like you describe one winter. It eventually stopped doing it though. From what I've learned so far, the first step in trouble shooting the CIS system is a pressure check. I haven't even done this yet myself though. Anyway, I don't think it would be your CSV since it only provides extra fuel for starting. I would check the Aux air valve though. It's located on the RH side, has an elec plug going to it and a hose on each side. It's made out of aluminum. From what I understand it's supposed to be open when the engine is cold and closes when it gets hot. You can take the outside hose off and look in there with a small mirror and flashlite and see what's up. It is a hugger mugger to remove the valve if you should need to do that. But you don't have to take it off just to see the position of the valve. I understand that they often get stuck (the valve inside). Anyway, just some fuel for thought if you haven't already solved the problem. Also, please understand that I'm not an expert on CIS by any stretch of the imagination. You may want to check out my thread and see if you have anything to offer from your experience. Thanks!

[BradH]

Bill,

Thanks. I'll try that, although the issue is happening less and less frequently. I appreciate you taking the time to respond.

Cheers,

Brad