1980 CIS Cold Idle Question
 

When my car starts up cold the idle is about 800 rpm and as the car gets warm it eventually goes up to about 1100 rpm. I have the hot idel set a little high because I was trying to get the cold warm-up rpm higher. I checked my AAR to verify it is correct for the car and that it is working as it should. I also checked my WUR and my my control pressure starts out low and increases as it should.

This is my first 911 so I cannot compare to other cars.

I gues my main question is I thought the warm-up idle would be higher than the hot idle.

It should be. You probably have less vacuum than when the engine was new, leaks at the injectors sleeves and seals and lower compression from wear, which means less air flow sensor height and leaner mixture at idle at "book" settings. My advice would be to disconnect and plug the vacuum retard, reset the idle speed and timing, check for vacuum leaks with an unlit propane torch and check the mixture with a dwell meter. You should get better cold starting and a higher cold idle during warm up.

You are correct about the cold start idle should be higher than warm idle. You have checked out the general conditions of the main culprits--WUR and AAR. I say "general" because you didn't quote your fuel system pressures and the ambient temperatures at which they were recorded. Your WUR may be in spec, or it may still be a bit out but it is the first thing to set correctly.

Are there any other symptoms when the car is cold, such as hesitation or popping through the intake or exhaust?

Have you had the mixture checked (with an exhaust analyzer)? If your system pressures are in spec and all components are working, mixture may be your next area to diagnose.

All in all, you may have a bit more information to provide to help get answers. Since this is your first 911, anything you provide may help without you realizing it. Use the search button on the top right of this page as there are literally hundreds of posts about CIS problems like yours. Keep us posted, help is on the way;)

lets go back to the AAR since its job is to raise the RPM's when cold. you verified that when it is cold, the AAR is open and when 12v is applied it closes. if you just checked to see that it is open, you could have reset the idle to compensate for the fact that it is open and not closing.

if the mixture is that far off, you would have popping when cold if too lean or surging when warm if too rich.

if the car was running fine at one time, i would not make any changes to the vacuum retard or timing until you get the problem fixed.

I should add some more info, I purchased the car not running and I rebuilt the entire engine. The car runs great and has a ton of power. When I got done rebuilding the engine and before I started the car, I went through the entire CIS system, rebuilt fuel dist, cleaned injectors, cleaned WUR. I also did a test were I would squirt all six injectors into individual graduated cylinder to ensure the injector flows were balanced..they all were right on at very little load, part load, and full load. I also checked for vacuum leaks with propane torch.

I also checked my fuel pressure it's at 75 PSIG, I set my warm control pressure at 54 PSIG and I set my cold CP based on temperature according to the chart in Bently manual. I also set my mixture so that the duty cycle of the frequency valve is at 50% with a fully warmed engine (I have a new o2 sensor installed). I also checked operation of my temp switch for closed loop operation and the throttle switch for closed loop operation. All are OK.

So this is were things get weird, when I set my cold CP according to the Bently manual chart the mixture is way too rich. So I modified my WUR so that I can adjust the cold CP with a cap screw and nut according what's in the forum archives. I have to set my cold CP to no less than like 48-45 PSIG when it is approx. 20 deg-F outside, these results are very repeatable.

What I did was set the cold CP by either pushing or pulling the air sensor plate to see if I was rich or lean. Currently I have it set where if you push up the sensor plate the car starts to surge and if you pull down the car stubles (these are very tiny pushes and pulling).

I just fee something is still not right with the cold start idle. Any suggestion?

My experience is that cold running and WOT AFR is better with a 30-40 duty cycle, closed loop. You are really only enriching the open loop mixture with this adjustment. Getting rid of the vacuum retard and resetting the idle speed to 950 rpm hot will give your cold idle speed a boost. Bosch normal plugs also seem to give the best cold starting performance, the platniums are not good.

45-48 is about 3.2 bar, correct? thats way too high for cold CP. should be down around 2 bar, i dont have a spec book with me. my 77 is about 1.8 bar cold.
you should be very lean and getting backfiring back into the air box, popoff vavle?

if you are talking about the cold mixture, how are you determining it is too rich when cold?
if you are saying it is too rich when warm when the cold CP is set to spec, then the bi-metal strip in the WUR is bad.

+1 on platinums bad.
i just put in NGK 7's copper, i can get them local and they are a tad cheaper. fixed my hot start problem.
i took the platinums out of my mazda truck and put in something like ac delco, runs better thatn it EVER has and gas mileage went up

The conversion chart lists the BP7ES in the range of the Bosch W5DC.
Were you aiming for a colder plug?

yes, the 7 looks VERY good. not to hi jack, i did a test with a (used) bosch W4. it never fouled or gave me any problems, except maybe sometimes it would not hot start like a bad check valve, but the plugs were used out of a 930.
i had been under a misconception of what a "hotter" plug meant and thought hotter meant better until i started reading about it a few years ago. what i have learned is that it is best to use as cold a plug you can without fouling and it is best to start with a cold plug and work your way up to a hotter plug. too hot a plug can promote spark knock.
reading some of what people say or ask here, i think there are quite a few that may not understand heat ranges either, or that really care much like i did in the past. i have read where people are raising compression but still run a W9
maybe i need to "encourage" boyt911sc to prove me wrong:D
if you want a compilation of what i have copied off the net, i will post it in a thread

I was going to look into doing this to run a little richer at WOT and warm-up. I'm glad you mentioned it. I forgot to mention that the vacuum retard is already off.

This is my problem, everything is in spec except the cold CP, I tried the lower cold CP from the chart in the manual and it's not even close to right. It is soo rich that my eyes start burning from the smell. I also verified that it is too rich by lifting and lowering the air vanve while the car is warming up.

maybee I am masking another problem but the only way to get the car to start ok when cold was to increase the cold CP, I am running the copper Bosch plugs