Idle issue when warm

[Monkeybackpack]

Need some advice on where to start looking. I have a 1987 DX 3 door without AC. stock carb. issue is high idle when the car is warmed up. approx. 1500rpm. Fast idle unloader works and will drop idle when cold to approx 900rpm. after driving idle creeps up to approx 1500. I have replaced all the vacuum hoses and checked the diaphragms, and everything appears to work correctly or not leaking vacuum. carb float works and idle mixture appears to be correct. I am stumped.
Here are replaced parts
thermovalve B
intake manifold gasket
waterpump
all coolant hoses
radiator cap
thermostat
all vacuum lines
fast idle unloader
choke opener
fuel filters (both)
fuel lines

just to clarify, system functions as it should when its cold but once it warms up is when the high idle issue presents itself. I have searched the forum and could not find a place to start looking. additionally, I have searched for a vacuum leak and have not found one. Any assistance or advice would be greatly appreciated.

[Howlite]

first check the dashpot diaphragm for leaks using a hand vacuum pump, the manual states

"If the dashpot diaphragm in the throttle controller is damaged or vacuum to the dashpot diaphragm
is blocked or leaks, correct idle speed can not be obtained. The idle speed will be excessively high after warming up the engine."

After that check the other diaphragms for leaks using the hand vacuum pump (don't forget about the advance timing diaphragm on the distributor)

check for vacuum leaks on the base of the carburetor and the intake.

Lastly you could do the brake booster test that is in the manual, perhaps it has vacuum leaks

Good luck, this vacuum sh*t is a pain

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[RI86DX]

I've been having the polar opposite issue. Car idles at just below 1k, like 900rpm, roll up to a stop light or stop in a driveway or whatever...bogs down to 150-200rpm and wants to die but keeps idling. This either happens after 10-15-20 seconds or sometimes it's instant. Pull off and I feel the car "lunge" forward a bit because it's suddenly getting a steady stream of fuel and is no longer struggling. This seems to only happen once the motor has warmed up just like in your case.

[Howlite]

I've been having the polar opposite issue. Car idles at just below 1k, like 900rpm, roll up to a stop light or stop in a driveway or whatever...bogs down to 150-200rpm and wants to die but keeps idling. This either happens after 10-15-20 seconds or sometimes it's instant. Pull off and I feel the car "lunge" forward a bit because it's suddenly getting a steady stream of fuel and is no longer struggling. This seems to only happen once the motor has warmed up just like in your case.

I am not 100% sure, but i feel like your carb either needs adjustment or rebuilding

You can adjust it by following A20A1 reply
https://www.3geez.com/forum/showthre...djusting-Order

But keep in mind if it is done incorrectly, it might make things worse

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[Howlite]

You could also try changing the fuel filters if it has been long since they were last changed

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[RI86DX]

My last episode of wonky idle woes was solved by Seafoam. I tried that this time except I made the mistake of putting it in with a full tank of fresh gas...should've put it in before the new gas and drove around and see if it did anything. The two fuel filters are new Fram units installed last year...I've heard bad things about Fram however.

[Oldblueaccord]

https://www.3geez.com/forum/showthre...tick-Dieseling

always check for loose boosters as well. All the keihin carbs had this problem. Sorry there are not pictures any more.

As far as the original poster make sure your car is running at operating temp. If you have the thermostat out and your car runs cold the carb could start getting into the cold run circuit with choke and high idle.

[RI86DX]

Will do, if I can't get the Keihin to stop flipping out I have the Weber K728 kit bookmarked on Carbs Unlimited..

[Oldblueaccord]

Carbs are pretty weather related,and elevation too, makes them frustrating to trouble shoot.