Question about 1991 Honda Civic

2 Answers

Idle fluxuates up and down consistantly - 1991 Honda Civic

Posted by on

2 Answers

  • Level 3:

    An expert who has achieved level 3 by getting 1000 points

    All-Star:

    An expert that got 10 achievements.

    MVP:

    An expert that got 5 achievements.

    Vice President:

    An expert whose answer got voted for 100 times.

  • Master
  • 662 Answers

Check the Idle Control System

Idle speed is controlled by the Idle Air Control Valve (IACV). The IACV changes the amount of air being bypassed to the intake manifold, in response to electric current controlled by the ECM. When the IACV is activated, the valve opens to maintain proper idle speed.

Symptom and Subsystems to Check:

1. Difficult to start engine, when cold--check Fast Idle Thermo Valve.

2. Fast idle out of spec, when cold:
a. Check Fast Idle Thermo Valve.
b. Check IACV.
c. Check idle adjusting screw (see Section C).

3. Rough idle:
a. Check hoses and connections.
b. Check IACV.

4. RPM too high, when warm:
a. Check IACV.
b. Check Fast Idle Thermo Valve.
c. Check hoses and connections, check Power Steering Pressure Switch Signal, and check idle adjusting screw.

5. RPM too low, when warm:
a. Idle speed is below specified rpm, with no load--check IACV and idle adjusting screw.
b. Idle speed doesn't increase after initial start up--check IACV.
c. Idle speed drops in gear (automatic transmission)--check automatic transaxle gear position switch signal.
d. Idle speed drops when AC is on--check air conditioning signal and IACV.
e. Idle speed drops when steering wheel is turned--check power steering pressure switch signal and IACV.
f. Idle speed fluctuates with electrical load--check hoses and connections, IACV, and Alternator FR Signal.

6. Frequent stalling, while warming up--check IACV and idle adjusting screw.

7. Frequent stalling, after warming up--check idle adjusting screw and IACV.

Additional Steps:

. Check Alternator FR Signal. Have alternator inspected, if idle speed fluctuates with electrical load. The FR signal communicates to the ECM how "hard" the alternator is working to meet the electrical demands of the car, including the battery and any loads which aren't monitored by the ELD. This square-wave signal varies in pulse width, according to the load on the alternator. The ECM places, approximately, 5 reference volts on the wire. The voltage regulator will drop this signal to approximately 1.2 volts, in proportion to alternator load. The ECM compares the electrical load (ELD) signal with the FR (Charging Rate) signal from the alternator and uses that information to set the idle speed and turn the alternator on and off. This helps fuel economy.

. Clean main ECM ground on thermostat housing.

. Reset ECM, by removing the 7.5 amp Back Up Fuse, in the under-hood fuse box, for 10 seconds.

. Replace PCV Valve, cleaning hose with brake cleaner spray.

. Substitute a known-good ECM. If symptom goes away, replace original ECM.

Check the ICM (Erratic RPM and PGM-FI System)

When the engine is cold, the air conditioner compressor is on, the transmission is in gear (automatic transmission only) or the alternator is charging, the ECM controls current to the Idle Air Control (IAC) Valve to maintain correct idle speed. Here's an overview of how the PGM-FI System works.

Background:

Various inputs to the ECM are TDC/CKP/CYP Sensor, MAP Sensor, ECT Sensor, IAT Sensor, TP Sensor, HO2S, VSS, BARO Sensor, EGR Valve Lift Sensor, Starter Signal, Alternator FR Signal, Air Conditioning Signal, Automatic Transmission Shift Position Signal, Battery Voltage (Ignition 1) Brake Switch Signal, PSP Switch Signal, ELD, and VTEC Pressure Switch.

Inputs are received and processed by the ECM's Fuel Injector Timing and Duration, Electronic Idle Control, Other Control Functions, Ignition Timing Control, and ECM Back-up Functions. These are the primary functional areas within the ECM.

Outputs from the ECM control Fuel Injectors, PGM-FI Main Relay (Fuel Pump), MIL (Check Engine Light), Idle Air Control (IAC) Valve, A/C Compressor Clutch Relay, Ignition Control Module (ICM), EVAP Purge Control Solenoid Valve, HO2S Heater, EGR Control Solenoid Valve, Alternator, Lock-up Solenoid Valve A/B (A/T), VTEC Solenoid Valve, and Interlock Control Unit.

Idle RPM:

Once you understand how the PGM-FI system is configured, it's easy to see how the ECM, Idle Air Control Valve, and the Ignition Control Module affect idle rpm. If the ECM's Electronic Idle Control function is not working properly, then it cannot properly control the IAC Valve. Likewise, if the ECM's Ignition Timing Control function is not operating properly, it cannot properly control the ICM (igniter). Obviously, idle rpm will also be affected if there's a problem with the IAC Valve or the ICM. As stated above, the ECM controls current to the Idle Air Control (IAC) Valve to maintain correct idle speed. This cannot happen if the IAC Valve is failing. The same situation exists if the ICM is failing. The ECM will tell the ICM to open and close the primary voltage circuit going to the coil and it won't respond properly. The result will be erratic spark plug firing and erratic rpm.

Conclusion:

If you are experiencing erratic idle rpm, try and isolate whether the problem is caused by the ICM (ignitor), IAC Valve, or the ECM. My experience has been that a failing ICM is usually responsible for the problem. Keep in mind that tachometers are connected directly to the ICM. Therefore, a fluctuating tachometer needle is often a dead giveaway. Heat and poor preventive maintenance (causing high secondary voltage to be discharge on internal distributor components) frequently causes the ICM (and coil) to fail. Besides performance, this is another reason why it's important to regularly replace spark plugs, spark plug wires, rotors, and distributor caps. Electricity will always follow the path of least resistance, even if it isn't the intended one. Our job is to ensure the intended path is the path of least resistance.

Ignitor (ICM) and Coil Replacement:

1. Disconnect negative battery cable.
2. Remove hex head machine screws, securing distributor cap to housing, using an 8 mm nut driver.
3. Move distributor cap and wires off to the side.
4. Remove machine screw securing rotor to shaft, using a #2 Phillips head screwdriver. It may be necessary to "hit" the starter once or twice, in order to rotate rotor for access to mounting screw.
5. Remove rotor and leak cover.
6. Unfasten ignitor wires, remove coil mounting screws, and set coil aside. Note: Removing coil first improves access to igniter.
7. Unfasten screws securing igniter to housing.
8. Remove ignitor from distributor and unfasten screws mounting ignitor to heat sink.
9. Coat back of new ignitor (or old igniter, if reusing) and male connectors with silicone grease. Silicone grease increases heat transfer to heat sink. Failure to apply silicone grease will cause the ignitor to quickly fail.
10. Mount ignitor to heat sink and reinstall ignitor, igniter terminal wires, coil, coil wires, leak cover, rotor, and distributor cap. Ensure female ignitor terminals fit snugly--crimp with pliers, if necessary.

AutoZone can test ICMs and coils for free. If you plan to keep the car, I would replace the ICM due the age of your Civic.

Posted on Sep 15, 2010

  • Level 1:

    An expert who has achieved level 1.

  • Contributor
  • 1 Answer

I had the same problem and adjusting the throttle position sensor worked for me..

California Lemon Law

Posted on Dec 24, 2011

1 Suggested Answer

6ya6ya
  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

Hi,
a 6ya expert can help you resolve that issue over the phone in a minute or two.
best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
the service is completely free and covers almost anything you can think of (from cars to computers, handyman, and even drones).
click here to download the app (for users in the US for now) and get all the help you need.
goodluck!

Posted on Jan 02, 2017

Add Your Answer

Uploading: 0%

my-video-file.mp4

Complete. Click "Add" to insert your video. Add

×

Loading...
Loading...

Related Questions:

1 Answer

What sensors will cause engine idle to fluxuate


intake air control valve,map or maf sensor.pcv valve or leak from vacuum hose.damaged or perished air box to throttle body pipe

Dec 24, 2015 | 1996 Ford Explorer

1 Answer

2005 GMC 2500 6.6 LLY I have rough idle, up and down, fluxuating. And my ECT gauge is all over the place too, but engine is not hot! Please help, it's my daily driver. No smoking either.


have the OBD codes read as will tell you which sensor/switch is at fault ,this will save you time and money as could be a number of things

May 07, 2014 | Chevrolet 2500 Cars & Trucks

1 Answer

Idle fluxuates up and down, stalls, ck engine does not come on. took on a trip, put 900 miles, ck engine lite came on. read a code maf/map p0068 came up. what to do


replace the throttle position sensor when this sensor fails the idle speed fluxuates may cause the trans to shift oddly also

Aug 22, 2010 | 2004 Dodge Durango

1 Answer

1996 ford bronco 5.8 litre, auto, engine idle has


Do you have a check engine light on? First thing I would do is unplug the IAC motor when the engine is warm. If the idle speed doesn't change you have a vacuum leak or a bad IAC motor. If the idle speed goes down you might have a bad TPS or IAC

May 31, 2010 | 1996 Ford Bronco

1 Answer

99 cabrio starts ok but dies when idling at stop light, hesitates under load sometimes also. intermittant idle fluxuation.


My first guess would be a bad idle air control valve if an inspection shows nothing apparent.

Dec 29, 2009 | 1999 Volkswagen Cabrio

2 Answers

Stalls at idle no fluxuation in voltage at iac


It is most likely the EGR (Exhaust Gas Recirculation) valve.
The valve is supposed to close when the car is idling and open other wise.

Inspect it / Replace it.

Hope this helps!

Sep 17, 2009 | 2003 GMC Sierra

2 Answers

1999 pontiac grand am 4 cylinder rough idle, rpms fluxuates


Most likely your throttle position sensor is faulty. You could have a vacuum leak as well. Most probable cause is a bad sensor. Is your check engine light on? Have you checked your engine codes? You can go to autozone.com and register for full free online repair manual.

Sep 14, 2009 | 1997 Pontiac Grand Am

1 Answer

Idle s 2300rpm when cold, then revs between 1500-2000, while..


maybe vacuum leak or intake manifold leak. sounds like components are doing there job adjusting to air intake, matching the amount of air brought in with the amount of fuel that it would demand to produce correct emmission quality. check this out. you can use carb cleaner to spray around your throttlebody and intake manifold and if the engine idle fluxuates you have a leak.

Apr 15, 2009 | 1991 Mazda 626

1 Answer

1997 ford probe engine fluxuates when idling


Hi jbloco, few things can casue this problem. Basic things first. Check your ignition componants like , spark plugs, wires,cap,rotor(if applicable). If you car runs good off idle then your Idle air control valve might be bad.

Aug 20, 2008 | Ford Probe Cars & Trucks

Not finding what you are looking for?
1991 Honda Civic Logo

1,908 people viewed this question

Ask a Question

Usually answered in minutes!

Top Honda Experts

yadayada
yadayada

Level 3 Expert

75744 Answers

Colin Stickland
Colin Stickland

Level 3 Expert

22114 Answers

Jeff Turcotte
Jeff Turcotte

Level 3 Expert

8123 Answers

Are you a Honda Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides

Loading...