‘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]

I read those pages earlier today and successfully didn’t get my head around it!
Bottom line for the tests conducted today. Both vacuum lines are staying connected. Good that what you’ve found confirms that stance.

Also, just tried a cold start and I’m right back to where I was before the spark plugs. I’d be really annoyed right now, if it wasn’t for the fact that the car is running so much better! I’m inching ever closer to getting all 76 ponies back in action! Getting plugs that seat properly made a noticeable difference and then retiming added a little more.
I mean it’s all good right? But as far as low idle on cold start, I’m right back to where I was after solving the high idle mystery.

Oh, one other thing. I used my fancy new timing light to get an empirical rpm measurement. When it starts I get a 700rpm idle. As it warms up, it climbs to the 850rpm I have set. It takes about two minutes to increase that 150rpm.
I’m aware that this is an inference, but 2min is how long it took the AAR to close when I bench tested it a few weeks ago.

Ugh, I hate being dumber than the mid-70’s!

[wonkipop]

I read those pages earlier today and successfully didn’t get my head around it!
Bottom line for the tests conducted today. Both vacuum lines are staying connected. Good that what you’ve found confirms that stance.

Also, just tried a cold start and I’m right back to where I was before the spark plugs. I’d be really annoyed right now, if it wasn’t for the fact that the car is running so much better! I’m inching ever closer to getting all 76 ponies back in action! Getting plugs that seat properly made a noticeable difference and then retiming added a little more.
I mean it’s all good right? But as far as low idle on cold start, I’m right back to where I was after solving the high idle mystery.

Oh, one other thing. I used my fancy new timing light to get an empirical rpm measurement. When it starts I get a 700rpm idle. As it warms up, it climbs to the 850rpm I have set. It takes about two minutes to increase that 150rpm.
I’m aware that this is an inference, but 2min is how long it took the AAR to close when I bench tested it a few weeks ago.

Ugh, I hate being dumber than the mid-70’s!

thats pretty close to how mine behaves on the cold start Van.
mine might even be a little weaker than that for the first 30 seconds/1 minute or so.

i should time it this weekend when i cold start.
will give you a comparison time for mine before it stabilises at its set warm idle around 850.

we will probably crack it eventually.
i'm trying to find that info i tracked down on aux air regulators/valves.
i know its the same as the one put into 924s and 944s.
but that doesn't get you any better off as its NLA for those cars too.
but there are a lot of very similar AAVs that ought to bolt straight in.
the only difference between them all is the rate at which they close and the size of the opening passage when cold.


only other thought i have is the electrical connection (wire) to the CHT.
you have a new CHT and got no difference.
i tested my CHT and it was ok.
but maybe the connection back to the ECU.
i'd have to look that up how to test at the other end.
have you done it?