‘74 1.8L L-Jetronic Cold Start Low Idle, Mystery solved! Options

[Van B]

Ok fellas, here’s the run down Aux Air Regulator (AAR) and Cold Start Valve (CSV)/injector both work fine. Many of you have also been keeping up with my high idle issue that we figured out.

But yet, when the car is cold, i.e. room temp, I don’t get the high idle I should on start-up. Instead she cranks a bit and then lumbers to life. Idle lopes around 700-800rpm and then smooths out as it warms.

In all other aspects of operation, the engine seems to be pretty happy.

Thoughts? Experience? (IMG:style_emoticons/default/confused24.gif)

-Van

See post #419 on page 14 for a synopsis of the outcome.

[Van B]

The temp switch is an interesting point. If in fact it's set for what humans would call cold weather and not what an engine would consider cold, then I may not have ever had it cold enough to truly activate the cold start. I found some document that covers some decent detail on the 912E L-Jetronic system and it mentioned exactly what you said.

Cold Start Thermo-switch:

912E = 30C/95F
914 = 15C/55F

That temp for the 914 makes zero damn sense!

I also found some wires on my dual relay that were loose. I don't understand how one side has the plastic plug and the other side looks like a hack job of different clips and pig tails?

[wonkipop]

The temp switch is an interesting point. If in fact it's set for what humans would call cold weather and not what an engine would consider cold, then I may not have ever had it cold enough to truly activate the cold start. I found some document that covers some decent detail on the 912E L-Jetronic system and it mentioned exactly what you said.

Cold Start Thermo-switch:

912E = 30C/95F
914 = 15C/55F

That temp for the 914 makes zero damn sense!

I also found some wires on my dual relay that were loose. I don't understand how one side has the plastic plug and the other side looks like a hack job of different clips and pig tails?

here is what i have Van.
From a L - Jet fuel injection manual for VWs generally.
see attached illustration.

3 different thermoswitches for the cold start valve are covered and listed with different bosch part #s.

would seem to imply fitting thermoswitches to suit different climate zones?
all three have different temp ranges but all having same spread of 18F between coldest and hottest.

but just to throw that off, I have another L jet guide that says the thermoswitch opens fully at 50F and closes above 104F. ?????? to me the 50 to 104 makes the most sense, as i would define an engine sitting at 104F as "cold" and needing a tiny squirt of start up fuel? or am i wrong.

anyway - all that means is thermoswitch opens cold start injector for full max timing at lowest temp, does not open it at all above the highest temp and in between its a diminishing amount of time the switch opens and the injector delivers.

in the 914 factory manual the test mentions the switch when tested below 50F should not open for more than 20 seconds. so 20 seconds is max amount of cold start injector delivery?

the truth is its really just got to work and more importantly switch the cold injector off.
to me its just a machine doing a synthetic couple of pumps on the gas pedal as you do for a carby car?

however -- thats not the fast idle warm up enrichment that takes over after the cold start injector does its job.

i know my cold start injector works, yours does too, but the enrichment cold idle phase is not quite right.





warm up enrichment is really controlled by 3 things as far as i can tell.

temp sensor 1 - in the intake air sensor of the Air Flow Meter. (intake air temp)

temp sensor 2 - the cylinder head temp sensor. (engine temp)

AAV - supplying the additional air for warm up.

and its kind of analogue like a clock, especially the AAV.

so one of those things is probably playing up and giving me the no fast idle warm up like you have on yours as well.

we tested all three of mine back 2 years ago and they all appeared to be working but i think this christmas i might re test and go over them maybe more closely.

i don't really worry about it at this stage as i know its running fine when its warm and i can put up with the little hitch starting the car cold every weekend and letting it get up to speed - and i never have to touch the gas pedal to start the car or keep it going during the warm up, so i figure its almost still all working after half a century and thats not too bad a situation for now.

[emerygt350]

The temp switch is an interesting point. If in fact it's set for what humans would call cold weather and not what an engine would consider cold, then I may not have ever had it cold enough to truly activate the cold start. I found some document that covers some decent detail on the 912E L-Jetronic system and it mentioned exactly what you said.

Cold Start Thermo-switch:

912E = 30C/95F
914 = 15C/55F

That temp for the 914 makes zero damn sense!

I also found some wires on my dual relay that were loose. I don't understand how one side has the plastic plug and the other side looks like a hack job of different clips and pig tails?

here is what i have Van.
From a L - Jet fuel injection manual for VWs generally.
see attached illustration.

3 different thermoswitches for the cold start valve are covered and listed with different bosch part #s.

would seem to imply fitting thermoswitches to suit different climate zones?
all three have different temp ranges but all having same spread of 18F between coldest and hottest.

but just to throw that off, I have another L jet guide that says the thermoswitch opens fully at 50F and closes above 104F. ?????? to me the 50 to 104 makes the most sense, as i would define an engine sitting at 104F as "cold" and needing a tiny squirt of start up fuel? or am i wrong.

anyway - all that means is thermoswitch opens cold start injector for full max timing at lowest temp, does not open it at all above the highest temp and in between its a diminishing amount of time the switch opens and the injector delivers.

in the 914 factory manual the test mentions the switch when tested below 50F should not open for more than 20 seconds. so 20 seconds is max amount of cold start injector delivery?

the truth is its really just got to work and more importantly switch the cold injector off.
to me its just a machine doing a synthetic couple of pumps on the gas pedal as you do for a carby car?

however -- thats not the fast idle warm up enrichment that takes over after the cold start injector does its job.

i know my cold start injector works, yours does too, but the enrichment cold idle phase is not quite right.





warm up enrichment is really controlled by 3 things as far as i can tell.

temp sensor 1 - in the intake air sensor of the Air Flow Meter. (intake air temp)

temp sensor 2 - the cylinder head temp sensor. (engine temp)

AAV - supplying the additional air for warm up.

and its kind of analogue like a clock, especially the AAV.

so one of those things is probably playing up and giving me the no fast idle warm up like you have on yours as well.

we tested all three of mine back 2 years ago and they all appeared to be working but i think this christmas i might re test and go over them maybe more closely.

i don't really worry about it at this stage as i know its running fine when its warm and i can put up with the little hitch starting the car cold every weekend and letting it get up to speed - and i never have to touch the gas pedal to start the car or keep it going during the warm up, so i figure its almost still all working after half a century and thats not too bad a situation for now.

Great stuff. I would add that as you find all the gremlins, stuff that used to behave badly often starts behaving well. Don't necessarily assume something is broken. I have found many of the simpler things (cht, aar) were working perfectly, just not when the hoses are messed up or there is a vacuum leak.