Hello Dan, 
I was up in your area for the EAA Air Venture at Oskosh.  I spent a week at Neilsville (east of Osseo and west of Marshfield)  It was my first trip to Air Venture. It was a real experience.  I flew a Vans RV6A two seater with the owner from Tucson. 

This Oh dark 30, I went out and started up the vette.  It was 63 degrees so this was a cold start - AC and heat off.  It idled smoothly at 750 rpm. Over the next few minutes is rose to 800-950 rpm so, I took it for a ride. I'm very happy.  So on return home I turned on the AC Norm and the idle went to 1100ish and higher when I switched to AC MAX.  I broke the control lever to the AC/Heater shortly after arriving in AZ but, I positioned the vacuum switch to the AC Norm position and just left it there.  I now suspect a vacuum leak at that switch.  Sort of a weird twist.  I did not even consider that. I'll see if Corvette Specialties has one in stock and go from there. 

Never a dull moment in the desert. 
Chip, I just got the email member notification from the Cross Fire folks.  Thanks again.   Keith
 

A vacuum leak in the A/C control panel will certainly drive ya nuts, but it is very possible...those things dry out over time, and leak like heck.
If you are still getting an O2 sensor code, you need to address that first, as the ECM may not be going into closed loop. It uses the O2 sensor to determine if the engine(exhaust, actually) is hot enough to begin controlling the fuel/air/ign ratios. The O2 sensor has to get at least 600*F to start working.
Another big issue on Crossfires is the top plate of the manifold, that the throttle bodies bolt up on. Those plates can warp, or the gasket may get spit out, and you'll have idle problems.

I'd be concerned about the O2 code. To set this code, the engine has to be running at road speed, part throttle(cruizing), for at least 5 minutes.
I can e-mail you the troubleshooting info for code 13, if you don't have it...

Hi Joel,     Thanks.  I do not have the troubleshooting info.  I have examined the area around and sprayed carb cleaner all around the bases of the Throttle Bodies and the entire area around the intake manifold.  I found a heater/ac control switch at Larry's Corvette Specialties and it should be here in a few days.  I knew that I needed to replace that but, did not put the two together.  Generally the idle is much better and I feel safer driving the car.  My email is good on the profile page. Thank you.

if you problems continue I have a scanner and would be happy to meet up with you to help.

Hi Philip, 
Thanks for the offer. 

I have received the AC/Heater control and hope that is the last piece of the vacuum puzzle.  I mostly fly up to Marana for breakfast at the airport.  My wife and I looked at a lot of properties up in that area and Picture Rocks. We are at the south end of Sandario Road near Ryan Field. We can get together at some point and see what the electronics say.  What's in your Nova.  I always liked the mid 70s Novas.

I'll be getting the control installed today.  I also have to replace the failing passenger side hood latch cable today.  I've also been reading the Crossfire Vault articles and that has been very informative.
Keith
 

Well the AC/Heater control unit went in ok.  It is nice to have the AC performing the way it should.  I now can get the MAX AC position and the AC works in town at stop lights!  That is very nice here in Tucson.  It was 94 F today.  After the new coolant and O2 sensor, 12 feet of vacuum tubing, EGR and raiser tube to the air cleaner and the new AC/heater controller the idle is steady at about 900 rpm when hot and 550-600 on cold start. This seems contrary to what I have been reading on the Crossfire Vault site. It should start go up to 1200 rpm then drop to 600-800 rpm.  Anyway the operation of the car is much better. It started out with an idle after cold start at 1500-1700 and would stay there for a long time making driving 15-25 mph a wild ride on the brakes. 

While I was in there I replaced both radiator hoses, removed the lower AC compressor mounting bracket and removed and replaced the sheared pivot bolt and replaced the AC/heater controller and the crossing hood unlatch cable(it was beyond time). The last two items I got from Larry at Corvette Specialties. Very nice doing business with him.  

The O2 code still shows up but, only decelerating. This weekend I'm going to trace the wire from the O2 to the ECM and replace it if I can. Thanks for all the help and support.
 
kwoody2010-10-29 20:48:08

Ok.  Here's more on the problem that still is intermittently troubling my baby. 

I have replaced the AC/Heat control panel and it works just fine.  For the most part, it starts cold and idles great. It starts out at 1000-1200 and then settles down to 700-850 rpm.  Early morning temps are now in the upper 30s and low 40s.  It runs ok for 10-15 minutes.  Once I get on the main road it is 65-75 into town or you'll get run over by the boys headed into town in their pick up trucks.  By the time I get into town the idle is up to 1200 to 1400 rpm and very little throttle is needed to go 45 mph.   This intermittently happens.  I don't get the O2 code till it gets warmer in the afternoon and then only after about 15-20 minutes. I did not find any trouble with the wiring from the O2 sensor. 

I am going to try using my compressor to blow into a vacuum line and see if I can find a leak that I've missed.  I have checked my check valve and it is good so nothing should get blown into the intake.  Has anyone done this before?  If so how'd it work out?
Thanks, Keith
 

I like the idea of using air to find a leak in a vacuum line..but..do not use an air compressor..you only need about 1 lb to 5 lb of air to find a leak..a smoke machine works good for this but you can make a tester yourself..supplies would be..vacuum hose..1/4 inch to 5/16 inch with various vacuum T's and straight ones..a shut off valve..I use a gas tank shut off valve for a lawn mower..a small guage is needed also..one that is gauged from .5 lbs to 10 lbs worked for me..that's it..you T in or connect to a line and blow in it..close the valve and watch the gauge..you will be suprised how easy and cheap this tool is..I use it all the time to find evap leaks in cars..if you find a line that drops pressure start at the other end of the line and work your way to the gauge..use pinch jaws to issolate the leak.  Fun stuff..and works on brand new cars..

Thanks Rich.   I have Sunday off.  I was out trying to adapt my compressor hose to a vacuum line when you posted.  Without the proper nozzle I gave up until next time.  I'll see what I can come up with for Sunday. I should be able to get that stuff at the local hardware store.  I did have a friend suggest that I blow cigarette smoke through it but, I quit smoking this year and that just does not thrill me much and I don't think the vette should start smoking at her age. I tried the headlight bypass switch and they worked after not being run today. (yesterday's vacuum)
I believe there is a check valve at the canister that holds the vacuum separate from the rest of the system. I also had suction at the brake booster too. That bypasses the vacuum check valve I think.  So, I could still have a leak upstream.  When I started it tonight; it idled just fine.  I won't run it again until Sunday. 

I'm so sad to hear the guys up north are putting away their cars. I'm still working on getting the garage project started so I can keep her out of the sun but, I do intend to keep driving her through the winter.
Thanks for the advice.
Keith
 

I almost hate to suggest this but since you have chased this high idle for so long it may be worthwhile to change out the ECM computer itself.  While not cheap, they are readily available.  I had to replace mine about a year ago and got it from NAPA for about $125 and my old core.  You will need to remove your old prom chip from the original computer and install it in the new one.  Just be careful not to bend any pins on the prom while changing it from one ECM to the other.