Cold idle

[heimtun]

When cold my car starts with ease and idles for about 20 seconds then stalls. I can keep it running with gas pedal. I can restart with ease but need to keep idle up with gas pedal for about minute or two to keep it from stalling. After this initial low idle - all good until the next cold (overnight cold) start.
Thoughts?

[stlrj]

Might need to up your idle speed setting to give your gas pedal a rest.

[T77911S]

the above is one solution but you could just be covering up a problem
need to check for
air leaks
fuel pressures
mixture
ignition-plugs,cap,rotor timing. (always check when running bad before getting into fuel)

[boyt911sc]

Originally Posted by heimtun

When cold my car starts with ease and idles for about 20 seconds then stalls. I can keep it running with gas pedal. I can restart with ease but need to keep idle up with gas pedal for about minute or two to keep it from stalling. After this initial low idle - all good until the next cold (overnight cold) start.
Thoughts?

Wayne,

You don't need to touch the accelerator pedal to get the engine to start in the first place. Place the gear in NEUTRAL, handbrake ON, get out of the car and reach for the ignition switch through the window. The engine should start without any further assistance. If the engine failed to start, you got some troubleshooting to do.

Check the following:
Fuel pressures
Ignition (sparks)
Source of unmetered air

And if you have been tinkering the fuel mixture setting lately, you got another thing to consider. Keep us posted.

Tony

[heimtun]

Thanks all!
No tinkering lately except first refresh was a new fuel filter. Will check ignition, timing and maybe new plugs next.
Again, I do appreciate input, but please read OP - car starts fine, idles fine for approx 20 seconds and then stalls with low idle. When warm - all OK including idle.

[stlrj]

Might check your pop-off valve to make sure it's seated and sealing properly, assuming this problem happened all of a sudden without any warning.

[heimtun]

No, not a sudden new problem - more of an ongoing getting better problem. New air filter and recent new fuel filter have improved the situation. Originally, the car would start easily (it has always started easily) and then stall right away - now it runs for about 20 seconds before it stalls. I'm assuming that instead of one major problem I have a number of smaller issues. I've checked for vac leaks and it seems that there are no major ones - there maybe some smaller ones that need to be tracked down. Removing oil filler cap when engine running does effect idle.

[boyt911sc]

Originally Posted by heimtun

No, not a sudden new problem - more of an ongoing getting better problem. New air filter and recent new fuel filter have improved the situation. Originally, the car would start easily (it has always started easily) and then stall right away - now it runs for about 20 seconds before it stalls. I'm assuming that instead of one major problem I have a number of smaller issues. I've checked for vac leaks and it seems that there are no major ones - there maybe some smaller ones that need to be tracked down. Removing oil filler cap when engine running does effect idle.

Wayne,

Do you have a set of fuel pressure gauge kit? This is a mandatory tool for fuel injection diagnostic test and if you don't have one, you will be wasting a lot of your valuable time looking for this mysterious culprit/s. Keep us posted.

Tony

[ossiblue]

Originally Posted by heimtun

No, not a sudden new problem - more of an ongoing getting better problem. New air filter and recent new fuel filter have improved the situation. Originally, the car would start easily (it has always started easily) and then stall right away - now it runs for about 20 seconds before it stalls. I'm assuming that instead of one major problem I have a number of smaller issues. I've checked for vac leaks and it seems that there are no major ones - there maybe some smaller ones that need to be tracked down. Removing oil filler cap when engine running does effect idle.

First, take Tony's advice and get a fuel pressure gauge set if you do not have one.

The immediate start you have always had is due to the cold start valve doing its job. The rapid dying--and now 20 second dying-- of the engine sounds like fuel "starvation" either through an air leak or insufficient fuel delivery. You've said air leaks are not the issue. To diagnose the fuel issue, to eliminate it as the cause, you will need the pressure gauge set. Of course, ignition, timing, and valve adjustments should be in spec before moving into the fuel delivery tests. Keep us updated.

[heimtun]

Thanks all for your recommendations. And I do have a fuel pressure test kit.
I've decided to run a bottle of fuel injector cleaner (BG 44K) though the system before my next move, which will include a fuel pressure test, etc.
I don't drive the car that much - so it might be a while before I go through a full tank of gas.

[Newfie911s]

I have the same problem, once the car warms up its not an issue.

Fuel Pressure Issue when cold is what I figure it is. I'm willing to live with it for now.

[Bob Kontak]

Originally Posted by heimtun

Thoughts?

One thing you might want to do is "cheat" the WUR leaning out by unplugging the connector to it when stone cold and before start.

The WUR takes 60-90 seconds, depending on SC model, to get to full lean when the thing is plugged in.

If you unplug it, it delays the transition from rich to lean.

Not the fix but if you miraculously have 60 seconds vs 20 of running well before the engine falters, you are on to an over lean situation necessitating the mentioned pressure gauges.

Side note. The $125 you spend on gauges is mandatory for DIY trouble shooting.

I bought a new -90 Bosch WUR for my 81 in the late 90's. Never ever has fallen out of spec. I know that because I have gauges.

[boyt911sc]

Wayne,

Next time you get a chance to work on your car, check the resistance (Ohms) reading of the heater for the WUR. BTW, do you have a -072? Keep us posted.

Tony

[heimtun]

Originally Posted by boyt911sc

Wayne,

Next time you get a chance to work on your car, check the resistance (Ohms) reading of the heater for the WUR. BTW, do you have a -072? Keep us posted.

Tony

Tony,
How do I ID the WUR? What resistance should I expect?
Wayne

[heimtun]

Here are two photos of my WUR. It would appear that mine does not have a vacuum line. Resistance is approx 10 ohms. Removing power to WUR did not improve cold idle. Folks mention a 3 digit WUR number... which 3 digits are they referring to on my WUR?

[gazzerr]

I think you have a 0 438 140 072.

[heimtun]

Originally Posted by boyt911sc

Wayne,

Next time you get a chance to work on your car, check the resistance (Ohms) reading of the heater for the WUR. BTW, do you have a -072? Keep us posted.

Tony

Looks like I do have a ...072 Resistance is approx 10 ohms. Your thoughts on 072?

[heimtun]

Originally Posted by gazzerr

I think you have a 0 438 140 072.

Yes.

[Jesse16]

I had this exact thing happen on my 87 this past weekend while visiting GA for a track day. Happened in the morning leaving the hotel until warmed up after a few miles. Then had it happen several times waiting on pit lane to go out. That time, the car was warm but not hot, never happened after car was fully warm. Is there a recommended fuel pressure set that has the right fittings to attach to the rail ?
I have a new fuel pump, could something else tell the fuel pump to stop working ?
The relay under my seat ?? That's an easy replacement also although can't see why engine temp would matter.

[boyt911sc]

Originally Posted by heimtun

Looks like I do have a ...072 Resistance is approx 10 ohms. Your thoughts on 072?

Wayne,

Your engine will always have this cold idle problem until you get a good working WUR. That's the reason I asked for your WUR's resistance. Check your cold control fuel pressure from start up to the time CP becomes WCP (warm CP) 4 mins. max. No need to run the engine just the FP with a fully charged battery. Record the control fuel pressure from start (zero sec.), and every minute after the start until the control fuel pressure stabilized to WCP. Do you have a set fuel pressure gauge kit?

I could lend you a good WUR-072 to try and test in your car. PM me if you are interested.

Tony