On Sun, 11 Mar 2007 19:48:39 -0700, jim beam
<spamvortex@bad.example.net> wrote:

>Hachiroku $B%O%A%m%/ wrote:
>> On Sun, 11 Mar 2007 21:00:58 -0500, the phelper wrote:
>>
>>> 1999 Civic EX 5spd
>>> 140k miles
>>>
>>> At idle, such as at a red light, *sometimes*, maybe 1/3 of the time to 1/2
>>> of the time, the tach will show the RPMS going up a few hundred, then back
>>> down several hundred more. Up and down, up and down... Only when the AC
>>> is on. Sometimes the RPMs have dropped significatly, and the engine seems
>>> to shake as if starved for gas or air or whatever.
>>>
>>> Vaccuum leak in the AC system?
>>>
>>> PS... not that it matters, but the AC control unit is on the frizt... this
>>> is the dealie next to the stereo, with the 3 knobs that control a) Which
>>> Vent, B) Temperature, C) Fan Speed. During the fall, I started having
>>> trouble with it, then in the winter all the fan speed knob stopped
>>> working. Temps have warmed up with Spring at hand, it works better now.
>>> I'll think about replacing it during the fall unless it dies in the
>>> summer. Mentioning this...just in case....
>>
>>
>> Off the top of my head, two things came to mind:
>> You have a vacuum problem, like you mentioned.
>> Your Air Flow sensor needs cleaning.
>
>honda don't have an air flow sensor. they have two air pressure sensors
>and they measure the differential between them. no cleaning required.
>
>>
>> Look for vacuum leaks or a stoppage, and you can try to cleanthe AF sensor
>> with carb cleaner or Lectro-motive (keep away from rubber or plastic).
>>
>> But, since you mention the AC problem, try turning the HVAC system OFF
>> totally and see if it goes away. If the compressor is off, then when the
>> system turns on, it may be loading the system too much and causing your
>> problem.
>>
>> As far as the fan control, these are controlled by a resistor pack,
>> usually located in the fan or behind the control; it looks like three or
>> four little springs. Does it work on some speeds but not others?
>>


Thanks Guys. Yep, it only happens with the AC on.

I don't know thing one of checking for leaks. Any ideas what that
should run costwise?

Thanks again.