What is the problem if carburetor idles high even when valves (mixture, idle) are at low adjustment?

Did you adjust the idle mixture screws ? Is this a two or four barrel carburetor and what make carb. Carter , Holley, Quadrajet etc.. What make vehicle is it ? Normally the idle mixture screws should be opened 1 and a half turns to two turns . counterclockwise from fully seated . Then you can set the idle screw to what the idle should be 600 rpm to 750 in drive . Most cars have a decal somewhere under the hood telling all these things !

Idling is adjusted differently on different vehicles. There are diesel engines, and two main types of injection, either from a high pressure pump to the injectors, or the so-called common rail injectors where injection is supplied by a high pressure pump but controlled by electronic signals.
Gasoline (petrol) engines have either carburetor systems where the carburetor turns the fuel into a gas before it enters an intake manifold which supplies the intake valves with combustible gas, or a common fuel injector which does basically the same, but the gas is produced by a single computer controlled sprayer. The final way of getting gas into the cylinder is to use injectors similar to diesel injectors, such as the VW Jetronic or K-tronic system.
Idling is adjusted on most engines by controlling the amount of gas which is allowed by a butterfly valve to pass into the intake system.
On an old style carburetor there is an air needle valve at the base of the carburetor which must first be adjusted to get the correct gas/air mixture necessary for the engine to idle, then the butterfly stop screw, which is also mounted on the base of the carburetor, but which is open to see. This will physically open or close the butterfly valve to increase or decrease the engine rpm.
However, we are moving more and more into the era of computer control, and the best answer to your question is, Take It To A Specialist!

there is a set screw in the front of the throttle body, to adjust it, but first why do you need to adjust it ? if low idle then it could be your TPS or IDLE AIR CONTROL VALVE, this valve is on the back of the TB and should be cleaned first, take the two.screws out which are torx heads and I think.a 25, once you have it out, take TB cleaner and a non lint towel and spray and clean, also clean the port where it sits in to, on these Dodges they are known for these to be carboned up, this would give low or high idle, also check to see if you have your 5volt reference on this sense, the TPS and crank sense, this one is hard to get to, it sits on top of your transmission bell housing on pass side. before you go touching the.idle set screw, check these and clean.idle air control valve first

High HC counts are due to a rich mixture, too much fuel. How does the truck run normally? To adjust the fuel mixture at the carburetor, make sure the truck is at operating temperature. Turn the idle mixture screw clockwise until the engine starts to lag then turn the screw back just until it runs smooth. Also make sure you have fresh oil as this could cause high HC's as well since fuel gets into the oil and make sure your PCV valve is operating correctly. If you can't get it adjusted correctly, you may have to pay a shop to hook it up to the emissions machine to get the mixture correct, unfortunately.
Hope this helps. Good luck!

High HC counts are due to a rich mixture, too much fuel. How does the truck run normally? To adjust the fuel mixture at the carburetor, make sure the truck is at operating temperature. Turn the idle mixture screw clockwise until the engine starts to lag then turn the screw back just until it runs smooth. Also make sure you have fresh oil as this could cause high HC's as well since fuel gets into the oil and make sure your PCV valve is operating correctly. If you can't get it adjusted correctly, you may have to pay a shop to hook it up to the emissions machine to get the mixture correct, unfortunately.
Hope this helps. Good luck!

Possible causes are clogged idle jet/fuel circuit in your carb.

Idle mixture too rich or too lean

Idle speed set too low.

2 airflow sensor out of operating range 3 coolant temp sensor out of operating range 4 oxy sensor indicates full rich 5 throttle potentiometer/airflow sensor... (low throttle pot signal with high airflow sensor signal) 6 throttle pot/airflow sensor...... (high throttle pot signal with low airflow sensor signal) 7 throttle pot...idle fuel adjustment failure(idle speed??) 8 intake air temp sensor...open or shorted circuit to sensor 11 Throttle pot at idle: Throttle pot idle trim out of normal range 12 Airflow meter: MAF signal out of range 14 Coolant thermistor: Resistance out of range or static during engine warm up 16 Air thermistor: Resistance out of range 17 Throttle pot: Out of range 18 Throttle pot/Airflow: Low throttle pot signal at high airflow 19 Throttle pot/Airflow: High throttle pot signal at low airflow 22 Fuel pump drive: ECU output to fuel pump relay 23 Fuel supply: Engine running too rich 24 Ignition Drive: ECU output to ignition Amp 26 Air leak: Engine running too lean 29 ECU self check 33 Injector Drive: ECU output to injectors 34 Injector: Looks for Injector dribble 37 EGR Drive: ECU output to EGR switching valve 39 EGR check sensor: EGR not working (normally pipe blocked) 44 Lambda (O2) sensor: Poor mixture control rich or weak (or misfire) 46 Idle speed Control valve: ECU output to Coil AB 47 Idle speed Control valve: ECU output to Coil CD 48 Idle Speed Control Valve: Stepper motor grossly out of position 66 Air pump: ECU output to air pump relay 68 Road speed sensor: Seen speed < 5km/h at high engine airflow 69 Drive/Neutral switch: Seen cranking in "D" or high airflow in "N" 89 Purge Valve drive: ECU output to purge valve
this is all I could find

carb problem or vacuum leak at carb base gasket or intake manifold

Isn't it fuel injected? More likely:
Pull plug wires one at a time, the one that has no effect isn't firing. Bad plug or wire.

Before you start check the status of your choke. One that is stuck on will cause a high idle. If the choke checks out, proceed to the following:


You should have what's called a 2 needle carburetor. A larger screw adjustment for idle, and a smaller for high speed.

Start by adjusting your low speed (idle) needle until you reach the desired idle. I prefer about 850rpms. Do this with the engine running and adequately warmed so that your adjustments are not thrown off by the automatic choke.

Next slowly open up the high speed needle. As you open it your idle speed will gradually increase. Adust it in 1/8 turn increments, pausing after each adjustment to allow the changes to take affect. Keep opening it until you stop increasing your rpms, then take it back 1/8 of a turn.

Next readjust your idle mixture screw so that your idle is back down to 850rpms.