993 surging after starting

[mart993]

Hi Everyone,

My 993 has a problem that I just cannot find a reason for. Most times after you start it, cold or warm, it will run fine for about 4 or 5 seconds, then start to surge, just as if you had pulled the choke out! It does this for between 10 to 30 seconds, then runs perfectly.

I have had the car 6 months, and carried out a full service a couple of months ago with new plugs, air filter, fuel filter, drive belts (genuine Porsche) distributor caps and rotor arms. It has just had a new clutch and DMF but the fault was there before this. The previous owner replaced the plug leads last year. I have replaced the DME relay, and checked the various temperature sensors. I have checked all pipes for tightness in case of vacuum leaks. When the car is surging, the resonance vacuum motor opens and closes the resonance valve. I have cleaned the Idle Control Valve which wasnt that dirty. A readout at the Porsche main dealer failed to locate anything. I dont have a fault code reader (could I build one?) and the car is a european (GB) version which I believe doesn't have a check engine light.

Any thoughts?

Mart

First holiday with the 993 - Loch Lomond, February

[Stealth 993]

Common, for it to rev up & down for a bit on cold start, more so on 95's. Mine will start go up to about 12-1400, then oscillate for about 3-5 times, then settle down.

If you think it is to much, pull out the ICV & clean it, a little search will tell you how, it's super simple.

[sml]

He said ... "I have cleaned the Idle Control Valve which wasnt that dirty"

[dlpalumbo]

I assume the surging is at idle. The resonance valve should be closed. If its cycling with no codes I'd suspect a wiring fault. Unplug the motor and see if the problem goes away. If the problem does go away, check wiring, or the motor itself.