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Jim
Grant has been working in the automotive industry for over twenty
years. In addition, Jim is an ASE Master Technician with advanced
L/1 certification. He works as manager and technician in his
family's automotive business in New Hampshire. He writes weekly
automotive consumer columns and is editor of an automotive newsletter
that is circulated throughout North America. |
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Jim Grant's Tech Tips
92
Honda Accord EX, Embarrassing Rattle and Idle problems
Q: I have a ‘92 4 door Honda Accord EX with
116k miles on it. It has been a good car except for a few things and I
think they might be related. When Idling the car vibrates like crazy!
It makes a very embarrassing rattling noise and sometimes while idling
the cooling fans will come on and turn off, repeatedly which makes a lot
of noise. The RPMS will rise and fall constantly.. anywhere from 400 to
1100 RPMS. I want it very badly to idle constantly at around 800 and not
rattle. If you can help me I would be so thankful! I've tried everything
and paid everyone to get it fixed but nothing seems to work.......Bobby
Byrd
A: More
often than not the rattle you’re describing is due to a loose exhaust
shield. The vehicle should go up on a lift and the exhaust should be inspected
for loose shields or brackets. Usually a little welding or stainless clamps
will fix the offending clatter. As for the unstable idle, there may be
underlying factors. When the computer in your vehicle senses additional
load, something that slows the idle speed, it will compensate by increasing
the engine’s idle speed. Additional loads come in different forms, like
the electrical load of the cooling fans, rear window de-icer or the A/C
system. Most of these components have a direct communication link to the
computer to let it know that a decision has been made to activate. The
computer knows that additional load is going to be added so, in response,
it will elevate the idle speed of the engine. Pretty smart, huh? Well
here’s where it gets dumb. All the computer understands is it’s either
time to up the idle speed or drop the idle speed. It has no clue that
there may be a bad switch causing the system to cycle on and off. A perfect
example is a failing cooling fan switch or an A/C system that is low in
refrigerant, (note that many A/C systems are activated when the defrost
mode is selected at the heater control). It is probable that if you have
the cycling cooling fan problem diagnosed you’ll like be on the right
track for correcting your unstable idle speed.
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