an6drew

I've recently replaced the airbox in my '82 SC, and repaired a couple of vacuum leaks in the process. Will it be necessary to get the mixture set again now that these leaks have been eliminated? I've also noticed that removing the oil filler cap now causes the revs to drop to ~400-500rpm. Previously the drop was barely discernible, presumeably because of the loss of vacuum in other locations. Is this behaviour expected with a well-running CIS system?

thanks,
Andrew

bones

Yes you've fixed the leaks by the sound of things . I can't see that mixture would be significantly affected though no harm in checking.

Bill Gregory

Andrew,

The revs dropping when you remove the oil cap is normal.

an6drew

Thanks guys, thats what I hoped. I've been having some strange idling behaviour since getting it all back together though. Idle has been high (1500-1800rpm). When it idles I have adjusted it down to ~900 w/ the idle screw, but after applying throttle the idle won't drop back down. The throttle linkage seems a little sticky (pedal return isn't too snappy) but even if I make sure the linkage @ the throttle housing is returned fully I'm still getting the same high idle problem. It just occured to me that I'd forgotten to reconnect the O2 sensor, so I'll do that tonight, but I don't think this would cause such behaviour? Any ideas- deceleration valve? Oh- I plugged the AAV while working on the CIS.

thanks
Andrew

Bryan Moore

Andrew -

When I replaced the airbox on my '80 SC, I had some driveability/idle problems similar to yours. After some expert advice, I traced the problems to using an incorrect part which came with the new airbox. Let me try to explain. My new airbox came with two plastic/bakelite vacuum fittings (for approx. 1/2" hose) - apparently identical except for the color, one red and one black. These fittings are, of course, on the most inaccessible side of the fuel injection system - something that becomes important later. When replacing the airbox, I used the new red fitting because the one that came off the car was red. It turns out that the fittings are intended for different applications and, apparently, color means nothing. On the one I used, the red one, the fitting is blocked off inside and the black one is not. When I (with great difficulty due to the location) installed the black one, all of my driveability problems went away. The wrench who pointed me in the right direction said "It happens all the time."

an6drew

Bryan-
thanks for the input. I think I remember reading an earlier post of yours to this effect. I ended up using a good used airbox. Some plugs/ fittings were attached, others were not, but I was able to reuse the old ones, and then there was 1 opening in the new airbox that the old didn't have at all which I needed to order a plug for to seal it off.
Is the piece you had trouble with #42 on the following diagram?
<a href="http://www.pelicanparts.com/911/911_Parts/1978-83/1-7-3.JPG" target="_blank">http://www.pelicanparts.com/911/911_Parts/1978-83/1-7-3.JPG</a>
Or was it something on the side/ underneath of the airbox:
<a href="http://www.pelicanparts.com/911/911_Parts/1978-83/1-6.JPG" target="_blank">http://www.pelicanparts.com/911/911_Parts/1978-83/1-6.JPG</a>
If it was the former, I think its the mounting piece for the cold start valve. I reused the old piece, although the replacement airbox came with one already attached. Not sure if this is what you're referring to though.
Do you remember where the 1/2" vacuum line went to from the airbox?
thanks,
Andrew

bones

if it's not the airbox problem i would re-check/lubricate your throttle linkages . I have hardly ever been happy with the throttle movement on my SC. I will sort it soon though!!

Bryan Moore

Andrew

It's been over a year so it's a bit hard to remember but I believe the part was #57 on the first diagram. I'll take a look tonight when I get home and let you know what I find out.

an6drew

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,