Idle adjustment screw base setting
 

1980 CIS 3.0 motor.

During my rebuild I fully disassembled the throttle housing. Does anyone know what a good base setting for the idle adjustment screw (big flat head screw)? I'm guessing you turn it all the way in and back it out so many turns?

I currently have a issue where it starts and immediately dies. Start it again and it will rev to 5k and immediately die. So first start has a low rev then second start high rev. I'm guessing it has something to do with fuel pressure, but would like to make sure the idle adjustment screw is set in a tolerable range.

Are you sure you're not just running on the cold start injector? Is the fuel pump coming on when you lift the sensor plate?

run the screw out a few turns. you should be able to keep it runing with the gas pedal until you can set the idle properly

are you giving it gas when you start it? is there a return spring on the throttle body? is the throttle sticking? any big air leaks? all vacuum lines back on? what about all the vacuum lines in the back that go to the decel valve and AAV?

On the first start it ran off the cold start valve. I had a big back fire through the intake. Pop off valve was a life saver. I then pulled all the injectors and lifted the sensor plate till there was fuel spray on all injectors.

vacuum lines and intake runner boots are all new. I have a CIS fuel pressure tester on order as of yesterday. In the mean time i'll just need to tinker till then.

Should there be immediate fuel spray when the sensor plate is lifted (micro switch disengaged) or is there a small amount of travel before the injectors fire? You would think it should be instant in order for the car to idle. This is assuming the plate is only lifted slightly at idle.

[QUOTE=T77911S;6251642]... is there a return spring on the throttle body? is the throttle sticking?... QUOTE]

My worse sticking point was the pivot point on the thansmission. Took it appart, clean and now it pivot freely.

[QUOTE=JJ 911SC;6252349] No it all moves freely. There's a brand new spring on it so it's got a good amount of tension on it.

Will update later after more trouble shooting.

Is proper timing set with leading edge or lagging edge of the rotor at the distributor mark? Leading edge would make sense due to arcing, but the 101 projects shows lagging.

The only time my 81 SC had big monstrous backfires through the intake was when the brass tube pulled out of the back of the throttle body. I do not know if the 80 has this.http://forums.pelicanparts.com/uploa...1315963171.jpg

The 80 does have that same tube.

the plate should have resistance as soon as you lift it, provided the FP is running. if you can lift the plate and there is a gap before there is resistance, the plunger is stuck.

update:

Finally got my CIS pressure tester in.

System pressure was dead on. Control pressure was 3.8bar with wur warmed up. I'll need to wait till tomorrow to check it cold. I adjusted the CO mixture screw (clockwise - richer) so that the slightest movement of the plate would fire the injectors. Before the plate needed to be moved almost a 1/4in before the injectors would pop.

Next I started it and it fired right up and stayed running. Although the idle was at about 2.5k rpm's and wouldn't respond at all to the idle adjustment screw. I let it run for 15-20mins while the smoke of the freshly rebuilt engine barreled through the neighborhood like a thick swamp fog. It seemed to run really well, but rich for sure. At least it sounded rich, but pulling the plugs showed otherwise. They were white/greyish which tells me a good mixture or on the lean side.

Only issue now is that I can't get the idle to drop. I've checked up and down for vacuum leaks and everything seems to be good. Checked the aux air regulator by applying 12v's and watching it close. Although it took around 5mins, but closed tight for sure. Another issue is the fuel system doesn't hold up to 1bar of pressure after shutoff. I'm suspecting a leaky cold start valve.

Next things to check are aux air valve and cold start valve (possible leaky cold start). Anyone have any tips or tricks on getting the cold start valve out without taking the motor out?

Matt

If you had a spare plug you could run 12v to and you should hear it click. Or maybe put your fuel pressure gauge on that line and see if it loses pressure.

Have the throttle stop screw been touched during the rebuild? On my car someone had adjusted this screw and the result was that the car didn't respond to the idle adjustment screw. Have a look at this thread:

http://forums.pelicanparts.com/porsche-911-technical-forum/625887-startup-idle-rpm-all-time-1977-2-7-cis.html

check your timing with a timing light

Forgot to mention in the update that I was able to set the timing with a gun once the motor would stay running. It was slightly retarded from my static guess.

That's a good point. I did completely disassemble the throttle during the rebuild. While reading the bentley lastnight, it says to turn the screw all the way out till the plate rests then turn it back in till it no longer rests on the throttle body. I'll double check it.

Update:

Removed throttle body and reset the plate stop and checked that the throttle switch was set correctly.

Checked the cold start valve for leaks which showed none.

Put everything back together and it fired right up, but I still could not adjust the idle. I then pulled the cap off the small nipple that goes to the aux air valve and the idle dropped to about 1k rpm and then seemed to respond to the idle adjustment screw.

I'm starting to wonder if the AAV is toast. Does anyone else have an 80 that can verify whether there is a cap on the nipple that goes to the AAV?

Matt

On the 80' you have the two "pancakes" one on top of the other. Only the bottom gets a vacuum connection. It's confusing because they both have nipples on the 80' which from every car after 80' that I've seen only the lower has the connection.

If you connect ported vacuum to that connection it does raise the idle, a lot. It's creating a bypass of the AAR when it's open. I only know this because I did the same thing. Years ago I thought my PO had left that disconnected, connected it and the idle jumped up. Of course CIS is "mystical" so I thought I had fixed one problem that was covering for another.

I did only have the decel valve connected to vacuum.

Main thing I'm trying to figure out is if the aav needs to be capped or left open. I take it yours is left uncapped?

Bently states that during starting the aav allows air to flow through the center port on the valve and once vacuum is present the valve shuts.

Mine doesn't/didn't have a cap, but I have no way of telling if it ever did.