Cold Start Valve problem?

On cold starting the rpms fluctuate from 800 to 1500 within a span of 1-2 seconds....any ideas? No other problems....once warm, five minutes, no hunting for revs and it is steady at 900 rpms at idle....symptom of cold start valve going?

83, 3.0 with CIS...

Michael Zois
Santa Barbara CA
PI# 18892
REA# 05214
'83 Cabriolet, euro

In California at this time of year, your cold start valve should not be activated at all. It is temperature triggered, it only operates in fairly cold temps (I think in the 50 degree range, but I'm not certain without looking it up).
In fact, in California, it hardly ever gets cold enough so that the cold start valve should operate.
I think it is something else.

Sounds like your mixture is a little off. If everything else is in order, you can try setting it by feel by inserting a 3mm allen wrench into the access hole on top of the fuel distributor. There's probably a plug of some sort in the hole to keep dust out. Mine looks like a wire with a loop on the end. Yank it out. put the wrench down into the hole and engage it into the screw (it's pretty deep into the hole). Note your starting position so you can undo. Don't push down on the wrench or the car will stall. Small amount of turn does alot. Go for smoothest (not fastest) idle. Adjust idle speed screw to maintain idle speed as you go. There are a few components that can cause this when they're faulty. If the symtom came on fairly suddenly, one of them may be bad.

Hope this helps,
Leon 78SC

[This message has been edited by leon (edited 09-04-2000).]

I doubt the Cold Start Valve would come on after the engine is already started. At least I've never heard of that.

My spec book shows no values of temperature and operation of the Thermo-Time Switch which, I believe, runs the Cold Start Valve. My experience with these (on water cooled VW systems of the same generation which seem very similar) is that the Cold Start Valve suirts most or all of the time on startup. Even with my engine warm, startup rpms go instantly to about 1500 for just a second, then down to normal. In colder situations the suirting and high idle can go as long as ten seconds.

Idle hunting has been a complaint with SCs before. Perhaps I'll look for an article (the Bruce Anderson kind). Leon is our ace closer for these CIS systems so I'd listen to him. I believe the articles I might find will identify problems with the Warm Up Regulator and that pesky Decel Valve. Plus, CIS systems have such HUGE air boxes that cavitation is present leading to irregular idle. My oxygen sensor system naturally causes a loping idle because of the fluctuations in O2 readings. It's kind of rhythmic but swings only a couple hunred RPM.

Again, larger swings have been reported and discussed in Pano or Excellence

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'83 SC

How long should the thermotime switch be on? I always get a very strong start, but then a very rough low idle for 3 or 4 secs (some times it stalls). It's almost like the cold start valve is injecting only when the ignition is in the on position, but as soon as the engine fires and I release the ignition, it stops squirting. Is this normal operation?

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Bill Krause
'79 911SC Euro

Mike, your car has an oxygen sensor taht makes it easy to adjust the mixture using just a dwell meter and the 3mm allen tool. I can provide the instructions if you need them.

But it sounds like your car runs fine when warm. Of course it always makes sense to check timing and mixture, but yours may be fine.

Various cold starting systems can be little gremlins that just need to be looked at one by one. I just read through the Anderson articles. It turns out that many SCs have cold running problems due to the Warm Up Regulator not getting the mixture rich enough. There is a procedure for adjusting them, and there is also a european version that fixes the problem. Dealing with this device is a slightly higher level procedure because it really should be done using a fuel pressure gauge. Again, procedures are available.

Auxiliary Air Regulators are easier to check. You measure resistance across the terminals. You can juice the terminals and time the closing of the valve. Use a light and a mirror if the device is hard to remove.

CIS troubles are usually just some device not working properly. I'll check my O2 sensor during cold startup today. I believe it gives a solid reading until hot. At temperature, they fluctuate very regularly. Maybe yours is fluctuating cold.

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'83 SC

My high idle at starup is at 1800 rpms, for 50 seconds! Does this mean my thermotime sensor needs replacing? It doesn't get very cold in Hawaii, but I know the cold start valve works upon startup all the time. Any suggestions? Thanks!

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Jeff
1976 911S

The high idle speed during warm up is not controlled by the thermotime switch, but rather by the aux. air regulator. The thermotime switch, cold start valve, and the control regulator work together to provide an enriched air/fuel mixture during cold starts and warm ups, the aux air valve, and the aux air regulator provide throttle body bypass air to increase RPM during warm up.

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Bill Krause
'79 911SC Euro

Ended up being too lean....thanks for the suggestions....narrowed down my search.