Weird CIS Idle

03-12-2003, 01:57 PM

Lookout- here comes another CIS counselling session

After replacing the airbox & reinstalling the engine I'm getting some strange idling going on- the car wants to idle around 1500-2000rpm. I figured this was due to a sticky throttle linkage (accelerator pedal isn't too snappy). I got it to idle @ 900 by adjusting down the thumbscrew, but after driving round for a few seconds it always returns to 1500-2000rpm, even when the idle adjusting screw has reached its limit. I checked & the linkage at the throttle housing is returning fully. The following could be helpful:
-I now remember that I completely forgot to connect up the O2 sensor- d'oh. I'll hook it up tonight.
-Reassembling the CIS definitely elimated some vacuum leaks (idle now drops significantly removing the oil cap)- would the mixture now be off... too rich? The mixture & timing were set before the airbox blew.
-I also plugged the AAV while things were apart
-The replacement airbox lacked the metal manifold which directed the cold start valve spray into the intake runners. I figured this wouldn't be a problem, and that the airbox was off an earlier car, but reused my original cold start valve.
-There was also a plastic cold start valve flange mounted to the replacement 'box. I may have used this one, rather than my old one. On my car this has a vacuum line that goes off to the auxiliary air system. Could it be that the flange I used has a 'dummy' closed connection for this vacuum hose? I never thought to check this?

Is there anything else that I should be thinking about? Any ideas appreciated.
Cheers,

Vipergrün · 03-12-2003, 02:04 PM

Andrew, what about your decel valve? Is it unplugged as well? Could be an overly rich fuel mixture...

tsuter · 03-12-2003, 02:08 PM

Did you remember to put back in or replace that big o-ring under the throttle body?

03-12-2003, 02:19 PM

Brad- I decided to leave the deceleration valve operational. Will removing & plugging the 3rd small vacuum line to this be enough to disable it if I want to?

Tsuter- yep I replaced that O-ring. I guess its possible it moved & didn't seat properly as I tightened it down.

tsuter · 02:37 PM

How about the brake booster line off the air box? I seen guys miss that and its a big air hole!

The flange for the CSV on the later air box is not blocked. Air from the AAV/AAR hose is directed through this hole in the flange directly into the internal manifold.

03-12-2003, 02:38 PM

hmmm, its funny you mention the brake booster line. I'm guessing this is the one the shoots off into the front left of the engine compartment, behind the cruise control servo? This hose literally snapped when putting everything back together. I took a look & as far as I can tell all this hose does is supply filtered air to the brake booster- it connects to the airbox under the filter- ie. BEFORE the air sensor plate. Anyway, I duct-taped it together & put it back, thinking it couldn't be introducing any unmetered air.
cheers,

tsuter · 03-12-2003, 02:47 PM

It is the threaded connection on the left lower side of air box next to the three manifold intake holes . see photo.
It is a big vacuum source for your power assist brakes. It will definitely suck in air if there are any leaks.

If that is good you also got quite a few hoses to the throttle body itself to check for proper connections.

Jdub · 03-12-2003, 02:51 PM

Are your distributor rotor/innards gummed up at all? Is the idle floating because the dist. isn't snapping back to idle?

The CO sounds like a suspect as well. The decel valve on my '78 is different than your '82 but I would suspect that as well.

John

03-12-2003, 03:24 PM

tsuter:
Thanks for the input. I must have been thinking of a cruise control vacuum hose. I guess the brake booster line isn't shown here: http://www.pelicanparts.com/911/911_Parts/1978-83/1-6.JPG because from what you describe it seems to branch off hose #35 in mine. The hose is a little brittle & could be the source of a vacuum leak I guess. I'll look into it, but if I had vacuum leaks before & didn't have this problem I don't think it'll be the sole cause of the idle issue?

John:
Rotor & cap are ~1000 miles old. Its possible things are a little gummed up from not being driven in 6 weeks? Whats the procedure to keep this all running smoothly- just clean it out & apply a drop or 2 of oil?

cheers,

Vipergrün · 03-12-2003, 03:32 PM

Quote:

Originally posted by an6drew
Brad- I decided to leave the deceleration valve operational. Will removing & plugging the 3rd small vacuum line to this be enough to disable it if I want to?

Yes, and you'll want to plus the line as well.

Good luck. Ain't CIS fun

tsuter · 03-12-2003, 03:37 PM

I would check all the throttle body connections. Vacuum line to distributor. EGR connections, decel valve etc. Any open ones would cause an air leak. Changing an air box gives you a lot of chances for an air leak. You said you plugged the AAV. How? AAR still functional?

03-12-2003, 03:58 PM

I left the throttle body & all its connections in place & basically removed the airbox from underneath it.
I was pretty thorough with reconnecting everything, and looking for any obvious vacuum holes. Because the engine was out, I was able to walk around & inspect everything at leisure (although I did completely forget to reconnect the O2 sensor until now!!!)
What is the EGR?
I plugged the AAV by duct-taping up the ends of both hoses, and then clamping them back onto the AAV inlets. The AAR could be questioned- It had a crescent-shaped opening when I had it off, cold, but I never had the high cold idle that I've heard is normal (ie. cold idle had always been the same as warm idle- 900rpm). Maybe I need to check that it does, in fact, close off fully. If I pinch the line when the engine's warm & running I expect idle wouldn't change if this is working?

Looks like playtime this weekend

tsuter · 04:53 AM

EGR Exhaust Gas Recirculation . Two small nipples on the back of the Throttle body with air lines attached.
Earlier you said that your repairs may have fixed several small air leaks. Possibly the CO was high before to compensate for the leaks. Now there is less of an air leak (AAR would still be behaving same as before) and the CO is now too high. High CO will cause a faster idle up to a point. As Jdub said if the air connections all seem fine then you should check the CO to verify it when the car is fully warmed up.
I know duct tape is useful but I would be using real vacuum plugs on those lines also.
Here is a picture of the back of my 78SC throttle body with most of the lines. Mine is not stock so many are capped off.

There is a whole thread on how to check your AAR. It closes by motor heat and by a 12V internal heater. Somtimes it can stick open which possibly yours is doing.

03-13-2003, 08:24 AM

Ok, so I fiddled around a little last night.
-Car starts a little hard cold- 3 or 4 secs of cranking when it would normally start immediately.
-My AAR seems to work fine. When cold its about 1/2 open. I checked it once the engine reached operating temp & it was fully closed. For some reason the AAR has never given me a high cold idle though??? Weird.
-I hooked up the O2 sensor. All this seemed to do was reintroduce the ~50rpm idle fluctuation

-Plugging the deceleration valve seems to have little to no effect.
-The tailpipe is fairly sooty. Think I'll get the mixture rechecked tomorrow.

I'll search some more through the archives. Basically the idle is ok when started from cold. When warm it is very reluctant to recover to idle speed & hangs around 1800. Sometimes it does eventually drop to 950 though.

thansk for the help,

Jdub · 03-13-2003, 08:34 AM

The fact that the AAR is not causing any changes to your idle should be investigated. The high idle should be choked down as that crescent you looked at becomes a new moon (there ain't much of an opening - it fluctuates).

John

tsuter · 08:48 AM

The only purpose of the decel valve is to allow a little air past when the throttle is closed or closing like on a shift to lessen the idle drop and speed of the vacuum ignition retard. If it isn't leaking it should not affect your start up or normal idle and warmup.
Sounds like CO is a good next looksee.

03-13-2003, 11:19 AM

That what I was thinking John. I need to study the vacuum diagrams more. I assume there must be something either blocked off or a hose incorrectly connected which is preventing any air ever getting to the AAR?

tsuter · 03-13-2003, 11:24 AM

It goes from the back of the Sensor Boot connection to the AAR to the CSV connection on the flange mount.

03-17-2003, 01:02 PM

OK- My idle problem is solved. The throttle linkage wasn't closing fully & not quite activating the switch at the end of its travel (not sure what the switch does??). After readjusting the linkage & setting the mixture I've now got a good steady idle @ 950rpm (well there is still a v.small fluctuation, but then the O2 sensor is still hooked up).

I still need to investigate why the AAR opening seems to be opening & closing ok , yet I'm still not getting a high cold idle. I'll pull the cold start valve & mounting flange (should be fun with the engine in) & check that the flange for the vacuum line from the AAR actually has an opening!

I'm also a little suspiscious of the cold start valve itself- starting is now a little hesitant when cold, occasionally firing up & then dying immediately the first attempt. Warm starting is fine.

thanks for all the help,

Jdub · 03-17-2003, 01:12 PM

That switch might be a cruise control thing?

For every tube carrying vaccum, never trust 1) age and 2) it, unless you can blow through it or suck on it and retain vacuum.

John