2003 Honda Civic Vibrates With AC On

[JavierG]

My buddy is looking into purchasing a used Honda Civic with 78k miles on the engine. He said that the dash vibrates excessivley whenever the AC is turned on. When the AC is off, there is no vibration.

What do you folks think it could be that is causing this? TIA.

 

[eljefino]

Low idle speed and/or bad motor mounts. Not a huge deal, likely.

 

[Smoky14]

MOTOR MOUNTS or compressor going out.

 

[Tegger]

Originally Posted By: JavierG
My buddy is looking into purchasing a used Honda Civic with 78k miles on the engine. He said that the dash vibrates excessivley whenever the AC is turned on. When the AC is off, there is no vibration.

1) What year and model?
2) Is the Check Engine light on?
3) Does your model have a tach?

Could be the A/C idle-up signal is not working. It's VERY unlikely to be the engine mounts.

 

[stockrex]

just raise the idle and see if that takes care of it.

 

[63Marauder]

If it's just the dash and not the car it could be the blower motor.

 

[2oldtommy]

A/C idle up signal would be the first place to chech as mentioned above. FWIW--Oldtommy

 

[Tegger]

Originally Posted By: stockrex
just raise the idle and see if that takes care of it.

ABSOLUTELY NOT.

The OP's Civic has an "idle up" circuit that is supposed to cause the PCM to raise the idle when the A/C kicks-in to compensate for the load on the engine from the compressor. OP should check the things I mentioned in my last post, then go from there. Under NO circumstances should he monkey with the idle speed (if he can at all) save making sure it's properly adjusted (if adjustable).

 

[rjundi]

Originally Posted By: stockrex
just raise the idle and see if that takes care of it.


Yeah just pull the round air cleaner off the carb to get at it. That's the ticket!

 

[berniedd]

The "idle up" circuit mentioned above is the idle air control valve (IACV). It is essentially an additional air bypass that is mounted ahead of the throttle plate. It is opened up by the computer when an additional engine load is sensed, like for example turning the aircon on. It can get clogged by dirt. It is easy to clean.

 

[Tegger]

Originally Posted By: berniedd
The "idle up" circuit mentioned above is the idle air control valve (IACV). It is essentially an additional air bypass that is mounted ahead of the throttle plate. It is opened up by the computer when an additional engine load is sensed

That's the point: the load must be sensed before the IACV is commanded to open by the ECM/PCM! The IACV doesn't just open up on its own! The A/C signal is sent to the ECM, the ECM thus becomes aware that the A/C has been activated, then it commands the IACV to open (and adjusts the fuel mixture to match) so the idle will remain steady.

If the ECM/PCM is not told that the A/C is on (no A/C signal sent), then it won't know to boost the idle to compensate for the load and you'll get idle vibration. If the vehicle has a tach, this problem will be very obvious, as the needle will drop and not recover. The Check Engine light may also be on.

And the OP never said what year Honda. Earlier vehicles had more secondary air inputs than just the IACV.

 

[hypervish]

Originally Posted By: Tegger
Originally Posted By: berniedd
The "idle up" circuit mentioned above is the idle air control valve (IACV). It is essentially an additional air bypass that is mounted ahead of the throttle plate. It is opened up by the computer when an additional engine load is sensed

That's the point: the load must be sensed before the IACV is commanded to open by the ECM/PCM! The IACV doesn't just open up on its own! The A/C signal is sent to the ECM, the ECM thus becomes aware that the A/C has been activated, then it commands the IACV to open (and adjusts the fuel mixture to match) so the idle will remain steady.

If the ECM/PCM is not told that the A/C is on (no A/C signal sent), then it won't know to boost the idle to compensate for the load and you'll get idle vibration. If the vehicle has a tach, this problem will be very obvious, as the needle will drop and not recover. The Check Engine light may also be on.

And the OP never said what year Honda. Earlier vehicles had more secondary air inputs than just the IACV.


It's a 2003 according the subject title.

 

[JavierG]

Originally Posted By: hypervish
Originally Posted By: Tegger
Originally Posted By: berniedd
The "idle up" circuit mentioned above is the idle air control valve (IACV). It is essentially an additional air bypass that is mounted ahead of the throttle plate. It is opened up by the computer when an additional engine load is sensed

That's the point: the load must be sensed before the IACV is commanded to open by the ECM/PCM! The IACV doesn't just open up on its own! The A/C signal is sent to the ECM, the ECM thus becomes aware that the A/C has been activated, then it commands the IACV to open (and adjusts the fuel mixture to match) so the idle will remain steady.

If the ECM/PCM is not told that the A/C is on (no A/C signal sent), then it won't know to boost the idle to compensate for the load and you'll get idle vibration. If the vehicle has a tach, this problem will be very obvious, as the needle will drop and not recover. The Check Engine light may also be on.

And the OP never said what year Honda. Earlier vehicles had more secondary air inputs than just the IACV.


It's a 2003 according the subject title.

Yup, it's a 2003. No check engine light but apparantly the SRS light comes on (oh great another issue). Thanks for all of the advice guys. I'm going to print this out and let my buddy read it so he knows what to look for and what may be the cause of his issue.

 

[Tegger]

Originally Posted By: JavierG
Yup, it's a 2003. No check engine light but apparantly the SRS light comes on (oh great another issue). Thanks for all of the advice guys. I'm going to print this out and let my buddy read it so he knows what to look for and what may be the cause of his issue.

Other things you can try in order to narrow down the problem:
1) Turn the steering wheel all the way to its limits. At full-lock, there ought to be no more engine vibration than usual.
2) Turn on the headlights and the rear window defogger. There ought to me no more engine vibration than usual.

If both turning the wheel to lock and turning on the headlights/defogger result in the SAME vibration as when the A/C is on, then there may be other issues.

 

[JavierG]

Originally Posted By: Tegger
Originally Posted By: JavierG
Yup, it's a 2003. No check engine light but apparantly the SRS light comes on (oh great another issue). Thanks for all of the advice guys. I'm going to print this out and let my buddy read it so he knows what to look for and what may be the cause of his issue.

Other things you can try in order to narrow down the problem:
1) Turn the steering wheel all the way to its limits. At full-lock, there ought to be no more engine vibration than usual.
2) Turn on the headlights and the rear window defogger. There ought to me no more engine vibration than usual.

If both turning the wheel to lock and turning on the headlights/defogger result in the SAME vibration as when the A/C is on, then there may be other issues.

Sounds easy. Thanks. Will do.

 

[MarkM66]

The SRS light is probably a factory recall issue. My '01 had it, dealer fixed it.

 

[artificialist]

I would have the SRS light scanned and fixed first. The car may have been damaged in a serious crash, and you wouldn't want it.

Sometimes cars run like that when the spark plugs are worn. Since it is a 2003, you have distributorless ignition, that reduces time needed to diagnose weak spark.