Suddenly, after warm-up: bouncing idle and overheating???

Discussion in 'General Motoring' started by M, Jul 17, 2004.

  1. M

    M Guest

    Hi. I'm baffled. I was planning (still am) to lend this car to a
    friend of mine in school who really needs a car. Any suggestions?

    My '91 Accord LX was running like a champ, smooth and steady. This
    morning, after not driving it for about two weeks, I started it and
    let it warm up. For the first four or five minutes, it was idling
    rock-steady at 1500RPM, typical for its warm weather warm-up.

    The temp gauge started to climb, and once it reached the usual
    temperature where the idle drops, it dropped. But instead of sitting
    at the usual lower RPM, the idle instantly started jumping up and down
    between 1100RPM and 1600RPM. Up, down, up, down. It was like a
    metronome.

    I pumped the gas a few times, and of course it revved, but it went
    right back to bouncing. It seems that when I put it in gear, either
    drive or reverse, it's perfectly steady again at the usual 600 or so
    RPM in-gear idle. Put it back in park or in neutral, and it starts
    bouncing again. One other brand new symptom to go along with this
    behavior: after another 4 or 5 more minutes, the temperature gauge
    suddenly starts climbing fast to overheat. I shut off the engine
    before it gets there. Did notice that only the passenger-side
    radiator fan appears to be running.

    Tried restarting the car a number of times, with and without letting
    it fully cool -- this behavior is consistent. Normal warm-up, idle
    starts bouncing the instant it drops the first time, 4 or 5 more
    minutes go by, then the engine starts to overheat.

    Help?! Many thanks for advice. (Besides, "take it in!" Yes, I'll do
    that if I have to.) Please post your idea(s) in this forum.
     
    M, Jul 17, 2004
    #1
  2. M

    Eric Guest

    The info below is from one of my prior posts regarding an '88 Accord LXi.
    The basic information still holds true for your '91. The link embedded in
    the TinyURL link likely won't work right now since the
    http://www.hondaautomotiveparts.com has been down most of the day (at least
    I can't access it). The cold start valves are basically the same on the two
    cars but they may be located in different places. If I remember correctly,
    on the '91 Accord it's the valve which is the furthest on the right on the
    front of the intake manifold as you're facing the engine and has two coolant
    hoses going to it at the bottom.

    [prior post]

    The most common problem associated with the idle cycling up and down is
    usually due to a lack of coolant flowing through the cold start valve. The
    valve is item number 8 in this diagram http://tinyurl.com/xj18. If the
    valve doesn't warm up as the engine warms up (from coolant flowing through
    the bottom part), the PGMFI system will misinterpret the condition and idle
    cycling results. The first thing to due is to check the valve and make
    sure that the lower part of the valve gets hot as the engine warms up. If
    the valve doesn't get hot, try bleeding the coolant and make sure that
    coolant is flowing through the valve. You can double check the valve as a
    source of the cycling by removing the two screws from the top along with
    the oval shaped plate and push down on the inner valve/plunger in the
    center. The cycling should stop if the valve is the problem. If the valve
    is getting hot and pushing the inner plunger down stops the cycling, then
    the valve likely needs to be replaced.

    Eric
     
    Eric, Jul 18, 2004
    #2
  3. M

    Eric Guest

    The info below is from one of my prior posts regarding an '88 Accord LXi.
    The basic information still holds true for your '91. The link embedded in
    the TinyURL link likely won't work right now since the
    http://www.hondaautomotiveparts.com has been down most of the day (at least
    I can't access it). The cold start valves are basically the same on the two
    cars but they may be located in different places. If I remember correctly,
    on the '91 Accord it's the valve which is the furthest on the right on the
    front of the intake manifold as you're facing the engine and has two coolant
    hoses going to it at the bottom.

    [prior post]

    The most common problem associated with the idle cycling up and down is
    usually due to a lack of coolant flowing through the cold start valve. The
    valve is item number 8 in this diagram http://tinyurl.com/xj18. If the
    valve doesn't warm up as the engine warms up (from coolant flowing through
    the bottom part), the PGMFI system will misinterpret the condition and idle
    cycling results. The first thing to due is to check the valve and make
    sure that the lower part of the valve gets hot as the engine warms up. If
    the valve doesn't get hot, try bleeding the coolant and make sure that
    coolant is flowing through the valve. You can double check the valve as a
    source of the cycling by removing the two screws from the top along with
    the oval shaped plate and push down on the inner valve/plunger in the
    center. The cycling should stop if the valve is the problem. If the valve
    is getting hot and pushing the inner plunger down stops the cycling, then
    the valve likely needs to be replaced.

    Eric
     
    Eric, Jul 18, 2004
    #3
  4. M

    Edmechanic Guest

    Well I think many things could cause a fluctuating idle but the
    overheating sounds ominous to me. I suspect a blown head gasket.
    Unscrew the oil filler cap and look for chocolate milk like residue
    (coolant in oil), also look at oil dipstick for chocolate milk. Also
    take out spark plugs and look at firing tips. Look for plugs that are
    inconsistent with others, greenish tint on insulator is coolant, also
    steamed clean look is bad sign.
    When engine is cold, remove radiator cap and look for oil, also
    leave cap off of cold engine and start it, if coolant shoots out right
    away could be combustion gases leaking into coolant system, probably
    at cylinder head.
    If this fails to find anything then concentrate on overheating.
    Is it a bad thermostat, clogged radiator, bad water pump(eroded
    blades), or maybe a jumped timing belt.
    A secret of good mechanics is that they can feel a missfire also.
    Also your varying idle and overheating could be due to an airleak
    .. An airleak could cause a varying idle and might smooth out with
    higher rpm. And a lean mixture runs hotter but in my experience not a
    real fast overheat.
    Hope this helps
     
    Edmechanic, Jul 18, 2004
    #4
  5. M

    Edmechanic Guest

    Well I think many things could cause a fluctuating idle but the
    overheating sounds ominous to me. I suspect a blown head gasket.
    Unscrew the oil filler cap and look for chocolate milk like residue
    (coolant in oil), also look at oil dipstick for chocolate milk. Also
    take out spark plugs and look at firing tips. Look for plugs that are
    inconsistent with others, greenish tint on insulator is coolant, also
    steamed clean look is bad sign.
    When engine is cold, remove radiator cap and look for oil, also
    leave cap off of cold engine and start it, if coolant shoots out right
    away could be combustion gases leaking into coolant system, probably
    at cylinder head.
    If this fails to find anything then concentrate on overheating.
    Is it a bad thermostat, clogged radiator, bad water pump(eroded
    blades), or maybe a jumped timing belt.
    A secret of good mechanics is that they can feel a missfire also.
    Also your varying idle and overheating could be due to an airleak
    .. An airleak could cause a varying idle and might smooth out with
    higher rpm. And a lean mixture runs hotter but in my experience not a
    real fast overheat.
    Hope this helps
     
    Edmechanic, Jul 18, 2004
    #5
  6. M

    Eric Guest

    OK, here's the a link for a picture depicting the valve for a '91 Accord,
    http://tinyurl.com/5yuk8. Honda lists it as a fast idle valve, item #8 in
    the diagram. This diagram shows the coolant hoses going to the fast idle
    valve, http://tinyurl.com/5ht67. If there's air trapped in the system, then
    it could block coolant flowing through this valve. Low coolant could also
    explain your overheating symptoms. You need to bleed the coolant using the
    coolant bleeder valve which is on top of the thermostat housing. Once
    you've done this and topped up the coolant to the correct level, you'll need
    to check the operation of the valve as in my prior post. Note that blocked
    coolant flow through this valve can also occur for other reasons besides low
    coolant. On one car I discovered rust plugging up the coolant passages in
    the electronic air control valve (EACV) which sits just to the left of the
    fast idle valve.

    Eric
     
    Eric, Jul 19, 2004
    #6
  7. M

    Eric Guest

    OK, here's the a link for a picture depicting the valve for a '91 Accord,
    http://tinyurl.com/5yuk8. Honda lists it as a fast idle valve, item #8 in
    the diagram. This diagram shows the coolant hoses going to the fast idle
    valve, http://tinyurl.com/5ht67. If there's air trapped in the system, then
    it could block coolant flowing through this valve. Low coolant could also
    explain your overheating symptoms. You need to bleed the coolant using the
    coolant bleeder valve which is on top of the thermostat housing. Once
    you've done this and topped up the coolant to the correct level, you'll need
    to check the operation of the valve as in my prior post. Note that blocked
    coolant flow through this valve can also occur for other reasons besides low
    coolant. On one car I discovered rust plugging up the coolant passages in
    the electronic air control valve (EACV) which sits just to the left of the
    fast idle valve.

    Eric
     
    Eric, Jul 19, 2004
    #7
  8. M

    Jason Guest

    Eric,
    Excellent two posts. Keep up the great work.
     
    Jason, Jul 19, 2004
    #8
  9. M

    Jason Guest

    Eric,
    Excellent two posts. Keep up the great work.
     
    Jason, Jul 19, 2004
    #9
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