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 ?

[Van B]

Steve, sorry for the delay, I’ve been traveling for work and forced to do things like socializing after hours lol…
Anyway, next time it’s all hot and steamy, you should grab hold of the throttle body and try to force the butterfly closed. If the idle drops back to where it’s supposed to be then I think you may have a worn TB that’s not seating and reveals itself when the metal heats and expands just enough to not seat properly.

[StarBear]

Steve, sorry for the delay, I’ve been traveling for work and forced to do things like socializing after hours lol…
Anyway, next time it’s all hot and steamy, you should grab hold of the throttle body and try to force the butterfly closed. If the idle drops back to where it’s supposed to be then I think you may have a worn TB that’s not seating and reveals itself when the metal heats and expands just enough to not seat properly.

I’m actually having the reverse problem - when hot and humid the idle drops. Sort of as if the less dense air and added moisture yields less O2. I checked the LJet guide and 74s don’t have the air temp sensor in the AFM.

[wonkipop]

Steve, sorry for the delay, I’ve been traveling for work and forced to do things like socializing after hours lol…
Anyway, next time it’s all hot and steamy, you should grab hold of the throttle body and try to force the butterfly closed. If the idle drops back to where it’s supposed to be then I think you may have a worn TB that’s not seating and reveals itself when the metal heats and expands just enough to not seat properly.

I’m actually having the reverse problem - when hot and humid the idle drops. Sort of as if the less dense air and added moisture yields less O2. I checked the LJet guide and 74s don’t have the air temp sensor in the AFM.

thats interesting about the sensor I in the AFC.
what L jet guide is that steve?

i have the service guide to the 74 model i downloaded from mr b's website - guide says its there. and it tells you how to check it - adding that it cannot be replaced.

factory workshop manual also says its there in the EFI section.

i mistakenly called it sensor 2 in posts above. sensor 2 is the cht.

hmmmmm?


not a bad theory of Van's that the AAV is playing up.
bloody things. a bit like a half century old pop up toaster when you think about it? (IMG:style_emoticons/default/smile.gif)