98 civic erratic idle

Discussion in 'Civic' started by loewent via CarKB.com, Oct 3, 2007.

  1. Good day,

    98 civic LX 5 spd with 285000kms.

    After being on the highway during my 35km commute, when I pull up at a red
    light, my RPMs stay at around 2500. After a few seconds, or if I pump the
    gas pedal, the RPMs go down to about 1200-1500.

    This just recently started happening. Don't know if its related, my AC
    recently stopped cooling. Sounds like the compressor doesn't come on. Is
    there anything in the AC mechanism that affects idle speed?

    Also, have recently done the following, all with OEM parts from the
    dealership:

    Spark plugs
    Distributor Cap
    Distributor Rotor
    PCV valve
    Air Filter
    Front wheel bearing
    rebuilt all struts
    all new suspension components front and rear
    4 wheel alignment

    When I did the distributor cap, I actually had to remove the distributor so I
    could drill out 2 of the bolts holding the cap on. (They were rusty and
    broke). I was expecting the removal of the distributor to be harder, but it
    was pretty much idiot proof. It appears that you can only put the
    distributor back in the block either the correct way or 180 degrees wrong.
    So if you are careful, you should be OK.

    Also, since my distributor had never been removed before, it was easy to put
    it back exactly the way I had removed it as I could see where the washers for
    the adjustment bolts had been before (good old corrosion at work here again).
    Checked the timing with a timing light after, and all is well.

    Note that the idle fluctuations occured before I did the tune up work (which
    was overdue anyway).

    I am also fairly certain the car is running pretty rich. Fuel economy is
    relatively poor (around 11-13km/liter or 25-30 US MPG or 31-36 UK MPG), and
    the exhaust pipe is pretty black. I have run several bottles of injector
    cleaner and Lucas Oil Upper Cylinder lubricant over the past few tanks and
    seen no real improvement here.

    The car has great performance, when you want to step into it, it accelerates
    really well. However, I have also measured fuel economy on a light foot, and
    the mileage is about the same.

    Driving pattern is mostly highway, we live about 20km outside the city.

    Any ideas of what I could check would be greatly appreciated.

    Thanks
    Terry in Winnipeg
     
    loewent via CarKB.com, Oct 3, 2007
    #1
  2. my suspension parts were aftermarket, not from the dealership... though I
    doubt that has any bearing on my idle issue.

    t
     
    loewent via CarKB.com, Oct 3, 2007
    #2
  3. loewent via CarKB.com

    Jim Yanik Guest

    Still too high.
    A switch to tell the ECU to increase the idle.
    No plug wires? They don't last forever.
    ECU trouble codes? your's is an OBD-2 model.
    you're probably overdue for a new O2 sensor(they last ~60-100K miles),and
    you need to get the ECU trouble codes read;a rich condition should set a
    code,light up the MIL light.
    Perhaps a bad throttle position sensor for the idle problem?
     
    Jim Yanik, Oct 3, 2007
    #3
  4. I agree the 1200-1500 is way too high.

    No trouble codes, I have a code reader.

    Plug wires have less than 100k kms on them. They are lifetime warranty bosch,
    and I did a continuity test and a resistance test on them, they are good.

    Where is the switch for the AC? I need to test it.

    I will check the TPS. any pointers?

    Thanks
    t


     
    loewent via CarKB.com, Oct 3, 2007
    #4
  5. are my symptoms indicative of a MAP sensor failure?

    t
     
    loewent via CarKB.com, Oct 3, 2007
    #5
  6. loewent via CarKB.com

    motsco_ Guest

    ------------------------------

    I think you've got air in your cooling system. I'd fill the reservoir to
    MAX and observe where it is each morning. Add more until is stays at MAX
    each morning.

    When the coolant temp sensors are high-n-dry, the computer has no idea
    where to set the timing / mixture.

    'Curly'
     
    motsco_, Oct 3, 2007
    #6
  7. Went for lunch and this is what I observed:

    RPMs = ~1800 when cold.

    After driving for 10 minutes, RPMs were around 1800-2200.

    I got to my lunch spot, and turned the car off. Then started it immediately.
    RPMs were at 600-700 (normal). Then I turned it off and went for lunch.

    Coming back to work, the RPMs were back up at around 1500-1800. When I got
    to my parking spot, I popped the hood and fiddled with the throttle a bit.
    By turning the throttle I was able to get the RPMs down to 600. So I'm
    wondering if this is a problem in the throttle body?

    As far as the coolant, all appears normal, rad is full to the top and
    resevoir is a little below normal. I haven't done any work on the cooling
    system for quite some time, so I doubt that an air pocket would develop
    spontaneously. I'll keep an eye on it.

    t
     
    loewent via CarKB.com, Oct 3, 2007
    #7
  8. loewent via CarKB.com

    Tegger Guest


    Have a look at your injectors. Do you have air lines running to each
    injector?

    How clean is your throttle body?

    How old is your thermostat?
     
    Tegger, Oct 4, 2007
    #8
  9. loewent via CarKB.com

    Jim Yanik Guest

    Maybe the throttle body has varnish built up and is keeping the plate open
    more occasionally? A thorough cleaning would correct that.
    Have you ohmed the TPS sensor? It could be getting worn at the "closed" end
    of the pot.
    there are ohms tests for MAP sensors.

    I had a CTS open on my 94 Integra GS-R.
    It's just a thermistor,an ohmmeter will verify it.
    Service manuals should list the ohms ranges for the various sensors.


    I'd like to note that O2 sensors can get "slow" near the end of their
    life,and not set a trouble code,but still affect operation.
     
    Jim Yanik, Oct 4, 2007
    #9
  10. Got some Throttle body cleaner, sprayed the throttle plate and tube. Also
    lubed the throttle spring where the cable attaches. Seems to be OK now.

    Is there a way to test my O2 sensors to see if they are bad? (or slow as you
    put it)

     
    loewent via CarKB.com, Oct 4, 2007
    #10
  11. No air lines that I can see.
    Not. I will clean it up good tonight, I did a basic cleaning to free up the
    spring and the throttle plate.
    Original. I have a new one, haven't put it in yet.
     
    loewent via CarKB.com, Oct 4, 2007
    #11
  12. loewent via CarKB.com

    Jim Yanik Guest

    I've read that you can use a oscilloscope to check them.
    Never done it myself.

     
    Jim Yanik, Oct 4, 2007
    #12
  13. loewent via CarKB.com

    Tegger Guest



    Then you don't have "that" kind of injectors.



    Make certain that thrpottle body is squeaky clean. There shoyuld be NO
    traces of gum or carbon ANYWHERE, especially in the tight sports.

    Use a brick or something on the gas pedal to prop the throttle plate
    open. Do not spray the cleaner dirtectly into the TB, bt spray it on a
    tothbrush and use that to scrub the carbon. Wrap an old T-shirt around a
    dry toothbrush and use that to wipe.


    I hope it's OEM and not aftermarket.

    An old thermostat can fool the ECM into thinking the engine is colder
    than it actually is. The ECM will then go into "warmup" strategy,
    feeding the engine excessive air and fuel, leading to a high idle.

    Fix the simple stuff first. Don't tackle hi-falutin' things like the TPS
    when the problem is about 99.99% certain to be a lot simpler than that.
     
    Tegger, Oct 5, 2007
    #13
  14. Yes, its OEM. I bought about $600 worth of parts last time I did my timing
    belt, and the t-stat is one of 2 leftover... I also have an oil pan gasket
    I've been meaning to use.

    Have doused the spring assembly where the throttle cable hooks up with a good
    cleaner, and have now lubed it using a good spray lube (no WD40!). The
    problem seems to have gone away.

    Definitely doing the simple stuff first. The shop manual says the TPS is not
    serviceable... IE the Throttle body has to be replaced.... OUCH. I start
    with cleaning the original assembly.
     
    loewent via CarKB.com, Oct 5, 2007
    #14
  15. loewent via CarKB.com

    Tegger Guest



    The linkage is not your problem. You should not have ANY grease there at
    all, as it will eventually attract dirt and begin to gum up, causing more
    grief.

    Clean that grease off the outside of the throttle body and leave it bone-
    dry.

    Make 100% certain the INSIDE of the throttle body is cleaned according to
    my previous (badly typed) instructions.

    If I were you, I'd replace the thermostat anyway. It's simply too old for
    comfort.
     
    Tegger, Oct 5, 2007
    #15
Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.