Idle Speed and Air Temp/Humidity Options

[StarBear]

As getting ready for the 2022 Northeast Gathering, I'm encountering a semi-recurring idle issue on my 1974 1.8L LJet FI. When outside air is cool and dry, idles just fine at 950-1000 rpm. When outside air is warm and humid, after warmup the idle falls off to barely running. I've just been adjusting the air flow screw (maybe 1.5-2 full turns) to open it. Of course, the reverse happens - if I preadjust the screw it idles near 1800 then settles down to 1100 after the engine gets totally warm (15 mins or so).
I presume (?) there SHOULD be some regulation, perhaps with the ECU or AFM, to monitor air temp and humidity and make adjustments automatically? I didn't have to manually do this adjustment in the past.
The AAR works and tests out fine. Just annoying to have to pull over after running a while and adjust the screw. (IMG:style_emoticons/default/dry.gif)
Your thoughts @Van @Van_B and @Wonkipop ?

[StarBear]

Update: Had a nice 30+ minute run today including highway. Air temp in mid 70s; a bit humid but not yet oppressive.
Car started at 1000 rpm then by 2-3 blocks rose to 1600 (my new seasonal initial preset). After 10+ min idle had dropped but only down to the desired 1000 rpm. Stayed in that mode until after highway and full time.
So, a) tightening the oil filler cap seems to have helped things from being so extreme and b) can live with a minor seasonal manual adjustments until a more permanent problem identification and solution.
(IMG:style_emoticons/default/dry.gif)

[wonkipop]

Update: Had a nice 30+ minute run today including highway. Air temp in mid 70s; a bit humid but not yet oppressive.
Car started at 1000 rpm then by 2-3 blocks rose to 1600 (my new seasonal initial preset). After 10+ min idle had dropped but only down to the desired 1000 rpm. Stayed in that mode until after highway and full time.
So, a) tightening the oil filler cap seems to have helped things from being so extreme and b) can live with a minor seasonal manual adjustments until a more permanent problem identification and solution.
(IMG:style_emoticons/default/dry.gif)

not saying its a temp sensor issue with yours @StarBear .

I'd have to find the reference again describing what happens when it does go out.
symptoms a little more extensive.

but the temp sensor is basically making an estimate of air density (via temp) and this triggers different amounts of enrichment by the ECU. so maybe this could be something going on.

there is a test for the AFM for our 74s in the factory manual.
its not really definitive as what it is testing is that mixed (modified) signal coming out of the AFM already adjusted. but its a basic test.

looks like the master @clayperrine has confirmed what its taken me 30 years to finally learn. so a slightly misbehaving temp sensor might cause some problems. not exactly sure how since idle conditions are set off the throttle switch and the afm is out of the picture i believe (at least at idle). i'm thinking the temp sensor comes into play off idle given that any signal from the AFM about temp has to get mixed in with the AFM flapper position signal. but what would i know. maybe that temp sensor does feed in somehow even at idle.

it was 10 C (50F) in your language yesterday when i cracked the 914 out. probably one of the coldest starts i have done since recommissioning it. did the usual start. nothing out of the ordinary. fell into its little hole for 2 minutes and then came on good.
5 minute warm up and then out for a drive. roof off, heater on. into a just spectacular sunset sky here thanks to the tongan volcano last year.

(IMG:style_emoticons/default/beerchug.gif)


as a thought, is it possible a misbehaving decel valve is causing this problem you have.
ie its getting stuck. sure fits a decel vavle high idle. but rather than being consistent and requiring adjustment its doing it intermittently? a thought.