Hello all,
I have a 1990 accord with an idle issue. The car runs great but once it gets warmed up, the idle drops. The drop doesn't seem to be the problem (it's at about 700) but when the fan kicks on, it puts a big strain on the engine. Sometimes it drops it to 500 and makes the hood physically shake. Once the fan is on, it seems to even out but there is still an overall vibration until it kicks off. No rattling, just a vibration. Furthermore, it seems to be more noticeable when I'm level versus on a slight incline. It doesn't seem to affect anything else since once I start driving, the rpm increase takes all symptoms away. I originally thought it was a battery issue but my battery was a little over 14 volts when I tested it. Does anyone know of something else I could check/test for this? Thanks in advance.

 

your issue would go away if you could increase your idle speed.
On carb'd cars 'twas easy - a screw at the carb, but don't know how to adjust idle on fuel injected cars.
I had a '93 MT with same concern, somehow went away, but can't now recall how/what. If I recall I'll post it up.

 

The idle speed is self-compensated by ECU, if the idle air control valve (IACV) and throttle body are clean.

Suggest going to DIY forum and read how to clean IACV and throttle body (both sides of plate and bore) w/ throttle body cleaner. Also check that IACV is functional (movement when 12V is applied directly).

Usually cleaning will restore correct idle control, however the base idle speed (idle speed w/ IACV disconnected) can be adjusted by turning the air bleed screw (near TDC on the throttle body entrance) to get idle speed near spec (600 rpm +/- 50 rpm not sure of spec).

good luck

 

Personally I would check the standing voltage on the battery. I would say it is lower than 12.5 volts. If the battery is on its way out when the fans kick on the extra amperage draw pulls hard on the stock alternator which adds a strain to the motor, thus causing the vibration at idle.

I def agree that the IACV should be checked and cleaned as well.

How old is the battery? Is their corrosion on the terminals?

 

If the airconditioning is running, that's not just the load of the fan. It's the AC compressor dragging down the engine. Maybe the AC is overcharged or the compressor is going bad?

 

Thank you all for the replies. Sorry for the delay but it took me a bit to get back to it. I cleaned out the IACV and there is a noticeable difference. The pull on the engine is significantly better but there is still a vibration as soon as the fan kicks on. It only lasts a second now since the idle is immediately adjusted but in that second, the hood and steering wheel still shake (not as much as before). Once the idle adjusts and the fan is going, the vibration is gone and the car is running fine. The battery is about 4-5 years old. Any thoughts on checking something else to get that initial shake to go away?

 

No, the AC is not running

 

Does the check engine light turn on when you first turn the key to the II position for about two seconds to do the bulb check?

Does the check engine light turn on or the D4 light start flashing when driving?

Are the maintenance items up to date like the spark plugs, air filter, distributor cap, distributor rotor?

 

The check engine light works fine but is not on or flashing. The distributor is new and the air filter and plugs look good. I did, however, find out that I need a new valve cover gasket set when I checked the plugs.

 

Check front and rear motor mounts.

Front mount is visible and easy to detect damage.

Rear mount can be seen from passenger side w/ a good light looking below behind throttle body. Following is procedure I used to find broken rear mount. Pull emergency brake and have a trusted helper (wife work's nicely!) to hold the foot brake securely. Start engine and place trans in reverse and goose rpms briefly to 1500-2000. Observe rear motor mount lift and you should be able to detect damage. I was able to observe the broken part and excess movement.

Replacement of rear motor mount is not terrible, but not easy either. Let us know if you plan to DIY this job for more instructions.

good luck