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1990 Honda Accord engine idles up an down

Tiny
ROSE2010
  • MEMBER
  • 1990 HONDA ACCORD
Engine Performance problem
1990 Honda Accord Front Wheel Drive Automatic 120000 miles

my car is getting the spark plugs black and the engine idle is not steady it goes up and down and the car is trowing black smoke. And if I clean the spark plugs they will turn black again, no oil on plugs just carbon black, like coated with heavy smoke. My idea is that it might be the idle control valve, but I could be wrong, anyone here no the right answer?
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Tuesday, June 2nd, 2009 AT 9:00 PM

1 Reply

Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
Hi rose2010,

When idling surges, it usually is due to excessive air getting past the throttle body and it could be due to :

1. IAC ( EACV)
2. Vacumn leakages, PCV, dislodged vacumn hoses, faulty brake booster etc.
3. Idle speed adjusted too high.
4. Clogged coolant hoses to IAC and Fast Idle Valve or insufficient coolant.

Plugs running black could be due to injectors, throttle position sensors, fuel pressure or ignition timing.

Testing would have to be carried out to verify the source.
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Saturday, June 6th, 2009 AT 3:46 AM

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