Ask Experts Questions for FREE Help !
Ask
    jtenny's Avatar
    jtenny Posts: 2, Reputation: 1
    New Member
     
    #1

    Jan 28, 2008, 09:04 PM
    1990 Honda Accord Fluctuating RPM in idle
    I have a 1990 Honda Accord that is fluctuating between 900 and 1400 rpms while idling and after the car has warmed up. What is going on?
    TxGreaseMonkey's Avatar
    TxGreaseMonkey Posts: 16,761, Reputation: 5597
    Uber Member
     
    #2

    Jan 28, 2008, 09:12 PM
    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 Accord.
    ntorrs's Avatar
    ntorrs Posts: 1, Reputation: 1
    New Member
     
    #3

    Feb 26, 2008, 01:00 AM
    I have the same car a 1990 Honda Accord. My car idles from about 800 to 2300 rpms. I have already had the distributer replaced (three times, then again with a dealership part) but that was when the car wouldn't start at all before at that time it would randomly not start right away but then it would after trying to start it about three or four times, waiting a few seconds between tries. I took my car to a different car care place and paid them to tell me why it is idling this way and they told me it was because I need to replace the throttle body or they could try and fix it for me. So I just replaced the throttle with one from a wrecking yard, and at the same time replaced the fast idle thermo valve but the car is still idling the same. I don't really understand how the whole ECM, IAC, ICM system works but I have a manual from autozone, a vacuum tester pump, and an new ohm meter. Does anyone have any suggestions of where to start or should I just take my car to a shop and have them fix it for me and let them charge me a swearword amount of money to do it and probably not even fix the cause of the problem?
    82-3870's Avatar
    82-3870 Posts: 1, Reputation: 1
    New Member
     
    #4

    Mar 10, 2008, 02:44 AM
    Quote Originally Posted by ntorrs
    I have the same car a 1990 Honda Accord. My car idles from about 800 to 2300 rpms. I have already had the distributer replaced (three times, then again with a dealership part) but that was when the car wouldn't start at all before at that time it would randomly not start right away but then it would after trying to start it about three or four times, waiting a few seconds between tries. I took my car to a different car care place and paid them to tell me why it is idling this way and they told me it was because I need to replace the throttle body or they could try and fix it for me. So I just replaced the throttle with one from a wrecking yard, and at the same time replaced the fast idle thermo valve but the car is still idling the same. I don't really understand how the whole ECM, IAC, ICM system works but I have a manual from autozone, a vacuum tester pump, and an new ohm meter. Does anyone have any suggestions of where to start or should I just take my car to a shop and have them fix it for me and let them charge me a swearword amount of money to do it and probably not even fix the cause of the problem?
    Sounds like you have a vacuum leak. Check all vacuum hoses for leaks. If you canít find any leaks remove the 2 bolts that hold the IACV on and pull it away and twist it enough that you can get into the back side and clean the ports with carb or brake cleaner & a toothbrush & flush it real good & put it all back together. If that doesnít work replace the IACV.

    If you are still having a problem with randomly not starting but works fine otherwise, replace the main relay located above the control box for the cruise control up under the dash. When these relays get old they cause the random wonít start problems like you described.
    graywhale's Avatar
    graywhale Posts: 4, Reputation: 1
    New Member
     
    #5

    Apr 28, 2008, 02:37 PM
    I had the same behaviour on my 1989 Honda Accord LXi - rev up and down when warm. Very annoying. But the fix was easy:

    What you most likely have is a dirty IACV a.k.a. Idle Air Control
    Valve that causes this. The sensors there can get dirty sending erratic signals. So I cleaned it without even uninstalling the thing, just loosening the two bolts and using a straw from the spray cleaner to get inside and in between the crack to clean the sensors and viola, the engine runs like new.

    Just be prepared for the rubber gasket to fall out. You'll have to fish it out and place it back as best you can before tightening the two bolts again.

    Here's more on this issue:
    How To: Clean Your IACV - Team Integra
    jtenny's Avatar
    jtenny Posts: 2, Reputation: 1
    New Member
     
    #6

    May 1, 2008, 09:54 AM
    Well, I appreciate all of the answers and they have helped me understand how my car works. Nothing was working so I took my car into a mechanic that I trust and come to find out the idle screw was sticking all the way out and so all he had to do was adjust the idle screw. I was trying to understand how this could have happened and realized that I had taken my car into the dealer a couple of weeks prior to the fluctuating idle for a different problem. It seems to me that this was created by the dealer. I have not liked their service and would not recommend taking a car into the dealer if you can help it.

    Again, thanks for the responses.
    builtontherock's Avatar
    builtontherock Posts: 58, Reputation: 1
    Junior Member
     
    #7

    May 7, 2008, 12:13 PM
    To my experince,on the top of the intake towards the back of the engin more to the drivers sid there is a little silver plate with two phillip screws take them off and they have a little plastic sleeve inside take two screw drivers and turn them down all the way.it will stop ideling up and down.
    Ambzc's Avatar
    Ambzc Posts: 2, Reputation: 1
    New Member
     
    #8

    Jul 23, 2008, 12:43 PM
    I have had the same problem with two honda accords, a 1990 and 1991. The fix both both was simple and inexpensive. There are two Valves that control the flow of your engine coolant, inside them there are springs that controls the flow. Basically it behaves like that because one of the springs has broken or worn out. If you shake the Valves you'll hear which one is broken and just replace it. Mine I replaced with a used one, it cost me $100 Canadian including labour.
    scapmetal's Avatar
    scapmetal Posts: 1, Reputation: 1
    New Member
     
    #9

    Aug 22, 2008, 08:35 PM
    Quote Originally Posted by Ambzc
    i have had the same problem with two honda accords, a 1990 and 1991. The fix both both was simple and inexpensive. There are two Valves that control the flow of your engine coolant, inside them there are springs that controls the flow. Basically it behaves like that because one of the springs has broken or worn out. if you shake the Valves you'll hear which one is broken and just replace it. Mine i replaced with a used one, it cost me $100 Canadian including labour.
    What valves?where?be more desriptive and thorough please!
    :mad:
    DonaldM_23's Avatar
    DonaldM_23 Posts: 86, Reputation: 10
    Junior Member
     
    #10

    Aug 28, 2008, 01:50 PM
    Quote Originally Posted by jtenny
    I have a 1990 Honda Accord that is fluctuating between 900 and 1400 rpms while idling and after the car has warmed up. What is going on?
    The answer is simple... Change your Vacuum control Box, Intake Manifold Gasket and Idle Air Control Valve... This will solver your problems
    Adrianpaul32's Avatar
    Adrianpaul32 Posts: 3, Reputation: 1
    New Member
     
    #11

    Oct 12, 2008, 12:40 PM
    So awhile back, I had some problems with my daughters car over heating. I take it to National Auto to have a radiator replaced, as well as a head gasket. I get the car back in about a week with additional problems. They broke a hose at the vacumn advance module, replaced costing 60 bucks. They failed to hook up a hose to the egr valve. Fixed. Then about a week or so, my daughter complains that there is something else wrong with the car. I take it out for a spin, and the engine light is on, and the rpms jump up and down, and I was beside myself. After looking at all vacumn hoses, I gave up. I jumped on line to see if I could trouble shoot it here. Found this forum about IACV and said that seems like the problem, so I pull it off. Guess what? Where it bolts onto the intake plenum, they had cut a small thin piece of metal and plugged it. I pulled the metal plate off, cleaned up the IACV, and her car purrs like a kitten. I am sooooooo mad at national auto!! :mad::mad::mad: I will never take any vehicle back there ever again.
    freequansee's Avatar
    freequansee Posts: 3, Reputation: 1
    New Member
     
    #12

    Oct 25, 2008, 08:26 PM
    I have 89 accord that had sperratic rpm. There is a bleed off for the coolant.if the cooling system has air in it it will cause the motor to run rough(rpm high and low).crack open the bleeder while the motor is running,let the air purge out ,tighten the bleeder and adjust the idle.
    player857's Avatar
    player857 Posts: 3, Reputation: 1
    New Member
     
    #13

    Oct 27, 2008, 11:26 AM

    I have a 1990 civic hatchback si and when it starts it idels rough then the check engine light come on and it idles smooth but when you go to giv it gas it cuts out half throttle and won't go any more it also tops out at 55 in 5th gear and when you go to down shift to get more acceleration it cuts the fuel out till it slow down to the speed it wants to opperate at what could be wrong?
    freequansee's Avatar
    freequansee Posts: 3, Reputation: 1
    New Member
     
    #14

    Oct 27, 2008, 05:01 PM
    Maybe you have a bad 02 sensor or fuel filter(filters) are clogged.
    player857's Avatar
    player857 Posts: 3, Reputation: 1
    New Member
     
    #15

    Oct 29, 2008, 08:55 PM
    No I put in new ones
    freequansee's Avatar
    freequansee Posts: 3, Reputation: 1
    New Member
     
    #16

    Oct 30, 2008, 07:04 PM

    Catylilic converter
    gto247's Avatar
    gto247 Posts: 1, Reputation: 1
    New Member
     
    #17

    Oct 13, 2009, 01:55 PM
    I am currently working on a similar problem with a 1990 honda accord.When starting cold it goes up to about 2000 R.P.M.S and then it starts surging between 850 to 2000 until it warms up.I plugged off the brake booster checking for vacuum leaks and it stopped surging.I replaced the booster and now it surges only a third of the time.Apparently this has helped.The cold idle is still too high,around 2000.It should be about 1600.I checked the air starting valve and found that the diaphragm on the
    Valve is leaking.The manual says to replace if leaking.I will be installing a new air starting valve soon.Maybe this will fix the
    Problem.Ill post the results soon.
    marcdam9's Avatar
    marcdam9 Posts: 1, Reputation: 1
    New Member
     
    #18

    Jun 24, 2011, 03:07 PM
    I went through just about everything that was said and just as I was going to replace my intake and IAC valve, fast idle valve, I checked my PCV valve and that was the vacuum leak into the intake. Replaced it and fixed the flucuating idle problem. Luckily, I found out it was the PCV valve and not anything else. Timed it, set the idle and now it purrs like kitty...
    mcgill1104's Avatar
    mcgill1104 Posts: 1, Reputation: 1
    New Member
     
    #19

    Feb 25, 2012, 09:57 AM
    1988 honda idles high have to put feet under gas pedal to bring it down and it cuts off every time you slow down or come to a complete stop.
    Waoky's Avatar
    Waoky Posts: 1, Reputation: 1
    New Member
     
    #20

    May 13, 2012, 10:12 PM
    I have a1990 Accord that Idles high when moving and shifting gears, also at idle as well. I have cleaned the Idle air control valve (IACV) and the Fast Idle Thermo Valve (FITV) which is right next to it. I have also cleaned the Air boos Controller which is right next to that. None of this helped the Idle except for the fast idle valve but it now idles up anyway even after retightening it. Any suggestions out there?

Not your question? Ask your question View similar questions

 

Question Tools Search this Question
Search this Question:

Advanced Search

Add your answer here.


Check out some similar questions!

1990 Honda Civic DX Auto Trans Idle Issue [ 3 Answers ]

I just got allot of work done on my Honda (new battery, tune-up, oil change, frans flush, radiator flush, ect). The car sat for a while with a broken axel, and drum. All this work is complete, but my question is this. What would cause the idle to stick (I think between 1.5K and 2k.. I have no...

93 Honda Del Sol Fluctuating Idle & Stalling [ 5 Answers ]

I have a '93 del Sol SI and for the past few years it's had a very rough idle, bouncing between around 1k rpm and 2.5k when the weather is normal to hot, and occasionally between 2k and 4k rpm when it's cold out or the engine is cold. Lately I've been having a serious stalling problem. Once my...

2003 Honda Civic has high idle 3000 RPM [ 2 Answers ]

My 2003 Honda Civic LX with 47,000 miles has worked perfectly until now. Since yesterday, every time I start it, the engine revs up to 3,000 rpm in neutral or park and 2,000 rpm if in drive. I can control the car with the brake, but it runs away with me if I stop braking. So I can't drive it...

2000 honda civic idle rpm [ 1 Answers ]

Does anyone know how to adjust this and what is the normal idle rpm


View more questions Search