Question about 1996 Honda Prelude

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Increase then decrease idle when engine is cold especially

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Cold engine idle surge. (problem)
RPM range of surge not stated
300-700 or 800 to 1500? (range is critical to diagnosis)

bad fuel
running summer fuel in winter (running old fuel?)
needs a tune up bad, see the list in the operator guide.
idle speed controller,sticking or EGR valve same. (clean them)
location not stated, so cant guess about local air temps.?
no other symptoms, lack of engine power? etc?
was it ok last week, or better, when was the last time it was OK?
1week, 1year?
surge , causes, on a tuned engine might be:
1: too lean. so lean the ISC can not control idle. rpm low, stalling
2: too rich, flooding, stalling, spark plugs foul (look at them)
3: weak compression in 1 or more cylinders.
4: bad spark.
5: air leaks, in the plenum causing , ISC to lose control.
why high RPM?

especially?
well that means it fails hot too.
and there is a simple tests. for hot surge.
is engine fully hot? 180F and holds solid there?
say rpm is about 800
and you turn on head lights, heater fan and (not AC) and defrost.
the RPM must hold or the ISC is failing.
ISC -= idle speed controls. (all EFI has this function)

Posted on Nov 02, 2013

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Posted on Jan 02, 2017

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Anonymous

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SOURCE: 1986 Honda Accord DX - too high idle on cold start

1986-1989 Honda Accord with Carburetor have a very bad habit that is little known even by most mechanics but easily fixed at home. The vacuum port on the choke opener that is connected to the intake manifold and both vacuum ports on the fast idle unloader get plugged up with nasty hard carbon almost as hard as metal. When this happens the choke sticks closed and the idle sticks on fast idle when the engine is cold and nobody can figure out why. All you have to do is attach a small drill bit to the end of a flexible socket-driver extension and put it in a variable speed drill that will let you run it real slow and carefully drill out the vacuum ports that are plugged. After they are nice and clean use a vacuum pump tester to make sure the choke opener and fast idle unloader are working before putting it all back together. It's amazing how much better the car runs after cleaning out those ports.

Posted on Sep 27, 2009

Anonymous

  • 388 Answers

SOURCE: the engine rpm's increase and decrease when in

Does your van have the V-Tec engine? If it does, you will have to take it to a dealer to get it fixed. What is happening is one or more of the solenoids under the valve cover is malfunctioning. The result is the surge in rpm's and the rough transition. You could try an indy mechanic but any mech worth his salt will tell you to take it to the dealer.

Posted on Oct 28, 2009

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Correct code P0504?


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I have a 1991 pontiac trans sport with a cold start engine surge. At cold start up the engine will increase and decrease in the rpm and sometime die but ofter the van worms up it seems to run ok.


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