Adjusting Idle Speed & Mixture – Civic ’92-95

by NinjaX on June 21, 2010

Adjusting Idle speed and mixture applies to Honda Civic 1992-1995.

Idle Air Control (IAC) Valve

Engine idle speed is controlled by IAC and fast idle valve. IAC varies amount of air by-passing throttle plate (into intake manifold) in response to signals from ECM. After engine starts, IAC opens for a short time to increase idle speed. Activation time is dependent upon engine coolant temperature. When coolant temperature is low, IAC is held open to obtain proper fast idle speed. After engine reaches normal operating temperature, IAC is activated only to maintain minimum idle speed.

Idle Air Control (IAC) Thermal Valve

Formerly called fast idle valve, IAC thermal valve allows additional air to by-pass throttle plate into intake manifold. Increased idle speed prevents engine from running erratically during warm-up. Valve is controlled by a thermowax plunger, which contracts when cold and expands when hot.

Idle Mixture

Idle mixture is computer controlled and is not adjustable. Maximum CO level is .1%.

Idle Speed

  1. Start and run engine under no-load condition at about 3000 RPM until cooling fan comes on. Let engine slow to idle. Turn engine off. Connect a tachometer. Disconnect 2-wire Idle Air Control (IAC) valve connector.
  2. Start and run engine at about 1000 RPM until engine speed stabilizes. Slowly release pedal until engine idles. Check idle speed under no-load conditions. Ensure all accessories, cooling fan and lights are off. If necessary, adjust idle speed by turning idle adjusting screw.
  3. Turn ignition off. Reconnect 2-wire IAC connector. Remove BACK-UP fuse from underhood relay box for 10 seconds to reset ECM. Restart engine. Check idle speed (after ECM reset) with all accessories off and transmission in Neutral or Park. Idle speed should be stable and within specification. Turn engine off.
  4. Start engine and idle engine for one minute with various accessories on. Check idle speed. Idle speed should be stable and within specification. If idle is not within specification, check vacuum hose connections. Check idle adjuster screw, fast idle valve and Idle Air Control (IAC) valve for proper operation.
  5. If idle components are okay, check MAP sensor, Electronic Load Detector (ELD), fuel injector circuit, A/C signal circuit, EGR system and lock-up control solenoid (if equipped) for proper operation. On Civic VX there has been a revision as per TSB Number HSN-0894-02 dated August 1994. Idle engine for one minute with headlights (low) ON, and check idle speed.


  • Honda Civic 1992-1995
    • Before ECM Reset (1): 370-470 RPM
    • After ECM Reset:
      • No Load:
        • Auto tranny: 650-750 RPM
        • Manual tranny:
          • Except D15Z1 MT: 620-720 RPM
          • D15Z1 MT: 550-650 RPM
      • Under Load:
        • Except D15Z1 MT: 700-800 RPM
        • D15Z1 MT: 650-750 RPM
  • Civic Del Sol
    • Before ECM Reset (1): 370-470 RPM
    • After ECM Reset:
      • No Load:
        • Automatic Tranny: 650-750 RPM
        • Manual Tranny:
          • Except B16A3 MT: 620-720 RPM
          • B16A3 MT: 650-750 RPM
      • Under Load: 700-800 RPM

Got questions or comments on how to adjust idle speed and mixture on 1992-1995 Honda Civic? Leave them below!

{ 14 comments… read them below or add one }

brandon June 28, 2010 at 5:31 pm

My 94 civic runs around 800 with no load but drops to about 400 with the a/c on. Isn’t the rpm supposed to increase with an added load?

spartanix June 29, 2010 at 1:02 pm

Could be a dirty or a bad bypass air control/idle speed control valve. Can’t recall what they call it on Civics. I’d say try cleaning out the throttle body first.

CHRIS October 23, 2010 at 8:42 pm

i just want to share my problem with 95 honda civic,maybe you can help me out there to fix this problem. My civic idle runs 700 rpm with no load when the aircon is on the rpm becomes low at around 300 to 400 rpm, sometimes the engine is off. What i’ve known/learned is, it should increase the rpm if the aircon is on. Isn’t it?
Please help!!!!!!!!!!!!!

spartanix October 26, 2010 at 2:28 pm

Check this out. It may provide some answers to your problem:

chris October 28, 2010 at 11:14 am

i did already diagnosis in the list of autorepair you’ve sent. This is a long time problem w/ my civic since i purchased 5 yrs ago. No problem w/ engine running with all accessories are on.headlight, sterio, fog lamp, except when the a/c is on(cold air). The rpm normal operation is 700 rpm but if the a/c is on it down to 300 rpm. and it ups to 500 rpm in neural or park. When i stepped on the gas to revolution the engine w/ a/c on the niddle of rpm down drastically to 100 to 200rpm and it back to 500rpm normal idle while in park or neutral.
Some say’s i have to replace the tbs or throttle position sensor and some say’s the idle air control. and some say’s its normal when a/c is on because of additional load. i’m kinda confused…sigh…..

raj November 14, 2010 at 10:37 pm

i have a 92civic 1.5l auto & in park or in gear it starts hesitating between 1500-2000rpm.I am disabled & am on a fixed income &don’t have lots of money.Can somebody PLEASE help me.Any advice will be greatly appreciated.Thank-you in advance

spartanix November 16, 2010 at 5:34 pm

Basic maintenance usually solves common problems associated with your civic. Replacing the spark plugs, air filters, vacuum hoses, etc should help. If you can take your car to the shop and have someone take a look at it. Get an estimate before you commit to any repairs.

john April 23, 2011 at 6:31 am

how to adjust the idle adjusting screw, left or right position, is this means by high to low. if im in front of the idle adjusting screw what is the proper position to adjust, either high or low or maximum to minimum

Justin May 12, 2011 at 3:36 pm

I have a fully built turbo d16z6 and my air/fuel ratio keeps goin between 16.7 and 16.8, and when i crank it up it idles about 2500 rpms, when i hit the gas a little bit it wants to bog down, is thats a good air/fuel ratio? if not how do i turn it up or down?

Doug February 20, 2012 at 10:17 am

My 1995 honda civic, 1.5, will not idel and is running rich, the exhust is building up black sult, runs rough, what do you think is going on. need help

robert May 5, 2012 at 9:39 pm

hi my name is Robert, and i’m having a problem with my Honda civic 1994.i start the car when in the morning and it start pretty good.but when the engine get hot and i turn off the engine then it doesn’t want to start again.i have to wait so i can start it .do you think is the iac motor?

zack October 24, 2012 at 9:22 am

Just had an engine replacement in 94 Civic EX, keeps throwing engine code 14 IAC valve. Replaced the valve, ECU still throwing code, idle impossible to adjust because of overheating/idle surge. Please HELP???

andy November 4, 2012 at 9:10 am

Its help for my idle problem

jose May 19, 2013 at 10:56 pm

95 honda civic ex runs good but , first when warm up,and run a/c steering wheel shakes help

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