Idle adjustment questions

[ngc414]

My manual shows the idle adjustment screw is on the left side of the throttle body and to turn in to lower and turn out to increase idle. Is that correct for a 79 911sc 3.0? Should the idle be adjusted while the car is running?

[dlagerstrom]

Yes. The idle adjustment is a large screw on the drivers side of the throttle body. I can turn mine with fingers, a screwdriver is not required.

While this will change the idle, you have to consider the other parts of the system as well. The idle, timing, and mixture are all adjusted together in the course of setting up the engine. I am still chasing some minor air leaks on my CIS system and it is tough to get the idle right with any air leaks.

Looks like you are in the process of getting yours up and running. What have you done?

[ngc414]

The car had a surging idle and was poping through the pop off badly at low rpm. I replaced the plugs, wires, fuel filter, dist cap/rotor with no luck. I checked the timing and it was fine. next I turned the richness 1/4 turn. the problem almost went away. I turned it a bit more and now it is alot better. I still hear a poping in the exhaust now every once in a while, but at least im moving in the right direction. Now the car idles around 1500 so I planned to bring it down a bit.

[dlagerstrom]

You should check your mixture with an exhaust gas analyzer or some such. I ended up getting the LM-1 to set it all up as I like to do it all myself but you can also take it to a local Porsche mechanic and have them set it up with a gas analyzer. I hear it only takes a few minutes to get it right.

[ngc414]

Originally Posted by dlagerstrom

You should check your mixture with an exhaust gas analyzer or some such. I ended up getting the LM-1 to set it all up as I like to do it all myself but you can also take it to a local Porsche mechanic and have them set it up with a gas analyzer. I hear it only takes a few minutes to get it right.

I found that the idle adjusment was already turned all the way in. Is the LM-1 a type of exhaust analyzer? where did you get yours?

[dlagerstrom]

Pelican used to have them but they are NLA. I got mine from a different web site that still had a few of the original ones. There is a new one coming out that looks nice but I don't know if it is available yet.

It has a wideband O2 sensor that takes goes in the exhaust to tell you what your air/fuel ratio is. With your 79, there won't normally be a bung on the exhaust so you would have to get one welded in.

Looks like the new LM-2 is out and shipping. I'm sure Pelican can get it for you.

http://www.innovatemotorsports.com/products/lm2.php

[dlagerstrom]

I posted in haste last time and didn't really address the clue you left.

If your mixture screw is in all the way, it is probably trying to compinsate for air leaks. The CIS system needs to have all the air going into the intake metered through the system. If there are air leaks, you will have to run extra 'rich' to compensate. In this state, you will not be able to get a good idle. If your system is original, you will want to look at all of the vacuum hoses, check if the airbox is cracked, check the boots that connect the airbox to the intake runners etc. I am guessing you have some pretty major leaks that are probably a combination of the above.

You have done the major tune-up items, but this needs to be sorted out.

Dig into it and let us know the state.

[ngc414]

Originally Posted by dlagerstrom

I posted in haste last time and didn't really address the clue you left.

If your mixture screw is in all the way, it is probably trying to compinsate for air leaks. The CIS system needs to have all the air going into the intake metered through the system. If there are air leaks, you will have to run extra 'rich' to compensate. In this state, you will not be able to get a good idle. If your system is original, you will want to look at all of the vacuum hoses, check if the airbox is cracked, check the boots that connect the airbox to the intake runners etc. I am guessing you have some pretty major leaks that are probably a combination of the above.

You have done the major tune-up items, but this needs to be sorted out.

Dig into it and let us know the state.

I think it may be a cracked air box like you suggested. I did find some good news. I was messing with the car and my neighbor (only met one other time) walked over. He said he was a porsche mechanic up until 2 years ago when he started at an audi shop.

[dlagerstrom]

Very Cool!!

My neighbors all seem to work for Best Buy and Target. Nice, but no help in the car department.