'83 911 SC: Starts and runs, but won't idle

[Woodyhfd]

I'm trying to revive a 1983 911 SC that has been sitting for a long time.

It starts right up, but won't idle smoothly and stumbles on throttle tip in. When I get the revs up to 3000 rpm or so, the engine sounds great. I tried to drive it, but it was bucking badly. It felt like the timing was off.

I have confirmed that I have compression, spark and fuel. I've checked the resistance of all the plug wires and they're in spec, cleaned the contacts in the cap and rotor, changed the spark plugs and confirmed that the timing is not 180 degrees out of phase and that all the plug wires are in the proper place. I've cleaned all the contacts and relays in the fuse boxes, every ground wire that I have found and any other electrical connector that I come across.

I should also mention that the car has Carrera tensioners.

Where do I look next?

[psalt]

Is the CIS Lambda system working ? If you are not familiar with this, search this site and read a little. Check the fuse and relay, then check with a dwell meter at the test port. If the system powers on and the FV is pulsed, then check the K Basic part, system pressure, control, etc.

[vash]

I bet your mixture is off.

[fred cook]

Check the coil wire for external arcs. Easy to do, put car in a dark spot and open the lid with the engine running. If you see a minature lightning show, replace the coil wire. Another place to check is to make certain that your oil filler cap is sealing. A vacuum leak there will affect the idle. Hope this helps!

[Dave Colangelo]

I dont know what you have done yet but I would advise getting a new distro cap and rotor, fresh spark plugs, change the oil, oil filter, fuel filter and air filter. This will only cost you maybe 100$ but can be the solution to some seemingly serious issues.

I would also check for vacuum leaks these cars can be very sensitive to vacuum issues. Typically it is the lines that go bad over the years and they can be replaced some what simply.

Once you have done these things you can start to consider other issues. The lambda system could be an issue, I have a 78SC which does not have the lambda system so I dont know much about it other than that it exists.

Regards
Dave

[70SC]

H2O in fuel

[Woodyhfd]

Fixed!

New relay under the passenger seat and the engine runs smooth as silk.

Thanks for the suggestions.