83 911sc just started to run slightly rough.
 

My 83 sc recently started to run slightly rough. I change the cap and rotor, but still running slightly rough. There is a valve gasket leaking oil, would that cause any vacuum leaks? I don't drive my car as a daily driver anymore. But I have it service every 6 month (minor service). Could it need a valve adjustment? It does not sound like the valves are making a different kind of noise? Any suggestions?
Thank you, JMAN :confused:

rough at idle or all the time?

It idle slightly rough, and as I drive it feel as if the engine is running on 5 cylinders. I notice at idle it smells sort of rich?

JMAN,

It just may be telling you that you need to drive it more. Or that the temps have dropped and you have a lean condition during warmup. Valve cover gasket will not cause a vacuum leak, but they are plently of potential leaks on old CIS, injector sleeves, o rings, boots, hoses, the best way to find them is with a propane torch. My suggestion would be to pull the spark plugs and take a look at them, clean and gap if OK, check wire ends, fire it up, run it until hot +10 miles, then hook up a analog dwell meter to the test plug and the CIS lambda will tell you what is going on. Much better than smelling rich, which is out of fashion lately. If you have a cold start stumble, my first recommendation is to disconnect the vacuum retard and reset the timing to 5 BTDC @ 950 rpm and the mixture to 30-40 dwell, this usually give the best cold start performance. If you still have a problem, you need to check the cold and warm control pressure and the system pressure.

Mine started running rough - mostly at idle, but also a little under acceleration. RPMs were down at idle as well. I ended up discovering an oil breather hose that was split. Fixing that fixed the rough running problem.

Thanks guys for the information, could you tell me where to look for that oil breather hose? Thanks...

Look behind the oil filler neck on the right side of the engine bay. There are two hoses about 1inch in diameter that are attached to the oil tank there and route back behind the engine. One can be replaced without too much trouble, the other will require at least a partial engine drop to get to. I did a temporary patch with parts from Home Depot until the new hoses arrived from our host. Now, it is a matter finding the time to partially drop the engine and install the hoses (they arrived this week). If this is your problem, good luck with it.

Sounds like the symptoms I had. The RPM's should drop slightly when you remove the oil filler cap, no change could be an indication of a vacuum leak. I found 2 intake gaskets leaking.

My symptoms were: Popping exhaust, rought idle, no idle change when oil cap was removed, could not adjust Idle with idle screw.

Good Luck!

plugs?
did it backfire? popoff valve installed or not closed properly? i found the pin sliding out on mine and have heard of others looking like they are closed but are not

fuel filter