Idle issue upon warmup..dies!

[tcesar888]

Hello!

Specs: 78 911SC Targa - stock!
Recent Change: Installed Cat-bypass
Normal idle: 900

Had a minor issue this morning… I warm up the car as normal (I live in Hawaii @ 75deg). I get to my initial intersection, and it dies idling while waiting for the light. I have had this happen a few times before; prior to the by-pass install...

What happens is the idle goes really low and eventually dies. Upon restart(s) it seems to not be able to find an idle; the tach "sweeps" between 0 to 2K (ie: vroom-pause-vroom-pause-vroom-pause-vroom-pause…dies…). I have to keep my foot on the gas to keep it from shutting down.

After the car seemingly warms up (more), everything is perfect!

When this happened before (intermittantly, and prior to the by-pass install), I figured I'd simply adjust the idle (up). You think its too rich due to the cat bypass?

Any thoughts or ideas?

Thanks in advance!

Tom

[ianc]

Same old story; get the pressure gauges and check your cold control pressure, then associated warmup items such as auxiliary air valve\regulator.

ianc

[tcesar888]

Thanks ianc! Will do...

[tcesar888]

Fix Update!

Narrowed the problem down to my Warm-up Valve Regulator Unit. The bottom/side vacuum port was not functioning... Working with a local shop I was able to replace the base (used) with a working valve. I reinstalled and readjusted the mixture and idle. Bam! Done!

If anyone knows...

In the process we determined I have a (033) Warm-up Unit verses the more desirable (045) unit. Does anyone have any background on the difference and reasoning? BTW, I replaced the base with a (045) base...everything works perfect.

Also, is it common for these to break or go out? Our host sells them for $500-$600...

Thanks again!

Tom

[Paulporsche]

Tom,

Great work!

There really is nothing more or less desirable per se for any given WUR. There is merely a spec for ea year. The 033 is for earlier 70s 2.7s and the 045 is for the later 70s 3.0s. It is more important to get the right control pressures for your engine than which WUR you use since, as you can see, they can be adjusted within a pretty wide range. also, if you overlay the graphs for various years, you will see there is a lot of overlap. The important thing is to have the vacuum hoses connected correctly.

You will also notice if you do a search, that most WUR malfunctions are due to simply being out of spec after so long in use, or from dirt accumulation in the filter, or some metal fatigue of the lever, rather than downright failure.

BTW I have been using an Audi 5000 WUR for my engine for several years. After all, who knows what control pressures a long stroke 3.2 should have? I've never seen any published.

[tcesar888]

Originally posted by Paulporsche
Tom,

Great work!

There really is nothing more or less desirable per se for any given WUR. There is merely a spec for ea year. The 033 is for earlier 70s 2.7s and the 045 is for the later 70s 3.0s. It is more important to get the right control pressures for your engine than which WUR you use since, as you can see, they can be adjusted within a pretty wide range. also, if you overlay the graphs for various years, you will see there is a lot of overlap. The important thing is to have the vacuum hoses connected correctly.

You will also notice if you do a search, that most WUR malfunctions are due to simply being out of spec after so long in use, or from dirt accumulation in the filter, or some metal fatigue of the lever, rather than downright failure.

Hi Paul,

Thanks for the clarification. With that, speaking with my tech... He said that there is an additional modification, with regards to the WUR, that I can make by basically routing the flows to and from the tank properly etc. He said that it is currently setup "backwards" (of sorts) to meet emmissions or something... He said that if I perform this mod I would improve performance and responsiveness. He said it intails drilling a small hole... I hope I am explaining this correctly. Are you aware of this additional modification? What and how?

Thanks again,

Tom

[Paulporsche]

I'm not sure about that. I can tell you that diferent WURs have their vacuum lines routed differently. Some have the vacuum attach to the top and the atmosphere to the bottom port, and some are the opposite. If you look @ the parts diagrams on this site you will see this. IIRC the vacuum line @ the bottom is to enrichen the mix during hard acceleration. That is why there is no line on the 80+ WURs. This function is performed by the lambda system, not mechanically.

If he is talking about fuel lines, then that's something else.

If you do this modification, please do a writeup w/ pics and post it.

[tcesar888]

Thanks Paul! I'll get some details upon my next visit and post something... THX, Tom