Engine At 100 Rpm When A/c On

funky · #1 05-23-2005, 12:27 PM

My 94 Honda Accord LX 4-dr 2.2l engine shakes the entire car when below 500 rpm. This mostly happens when the A/C is on and I have the car in D4 (sometimes it happens when in park, but not usually).

What do I need to do to fix this? I do not know much about engines. Is this a big problem or is this easy to fix? tune-up?

thanks!!

AccordCodger · #2 05-23-2005, 02:04 PM

Most likely, motor mounts.

funky · #3 05-23-2005, 02:14 PM

the car idles normally at 500 rpm, with A/C on it drops to 400rpm, lately down to 200 or 100 rpm.

AccordCodger · #4 05-23-2005, 08:21 PM

bad motor mounts and a dying compressor?

funky · #5 05-23-2005, 09:30 PM

when the compressor dies, does it draw more power from the engine? is that what you are saying? sorry, i'm not a mechanic of any sort :|

i was thinking that the engine was just not idling fast enough...

excoupe23 · #6 05-23-2005, 11:00 PM

your normal idle is suppose to be at 750 you can vierify that but looking at the diagram on your hood. Raise the idle w/ a screwdriver. It should be on the throttle body like on my 91 accord.

funky · #7 05-24-2005, 06:52 AM

sorry for being stupid, but where is the throttle body and what does it look like?

thanks so much

ProMan · #8 05-24-2005, 08:32 AM

Motor mounts has nothing to do with the engine RPM. The shake is due to the low idle.

Normally when the AC is on, the engine RPM will be pulled up to compensate the load generated by the compressor. It's done by either an idle-up valve or directly by the idle speed control valve. So, since your RPM drops when you turn on the AC, your compressor should be working fine. And, before you find the real problem, I suggest you don't adjust the idle speed yourself. You can bring the idle speed up but may adversely affect the engine performance.

Another guess, since the engine drops to 100 and shakes badly with load, it's possible that one of the cylinders is not working. You can check it by pulling out the spark tubes one at a time to disable that cylinder. The engine should jerk when you disable a working cylinder. If the engine runs without any noticable difference when you pull out one spark tube, that cylinder does not work already. Let me know the results if you are able to test it.

If you don't know too much about vehicles, I suggest you find an honest mechanic for help.

funky · #9 05-24-2005, 08:39 AM

i'm going to take it in to a mechanic this afternoon. will let you know what he finds. btw, does anyone have any recommendations for a good mechanic in the sarasota/bradenton, fl area?

jeffcoslacker · #10 05-24-2005, 04:35 PM

If I'm not too late, take a look at this thread.

http://www.automotiveforums.com/vbul...d.php?t=408653

jeffcoslacker · #11 05-24-2005, 04:38 PM

P.S., yes, your idle is too low, if all cylinders are firing properly.

Idle will pick up as the mixture is richened. Then set base idle once an even idle mix is achieved. You may not even have to mess with the idle.

One other possibility is a vacuum leak, which will lower idle speed, increase idle roughness, and make it prone to stalling under load at idle (i.e. A/C on, etc) If the problem came on suddenly, this would be the first thing I'd check.

funky · #12 05-24-2005, 08:36 PM

thanks for the help everyone...i had a mechanic increase the idle rpms up a notch and the car is running smoothly now.

the 94 honda accord throttle body is a bit different, and it was quite hard to adjust the idle rpms -- had to really have 2 people, one to hold the throttle out of the way while the other adjusted the screw/nut. not very straightforward. we basically adjusted it until the idle with A/C on was at 750 rpms.

i was wrong by saying it was idling at 500 rpms, i mistook the light notch on the dash for 500, not 750. it was idling (without A/C) at 750rpms. after the adjustment, it idles at about 850-900 rpms without A/C, 750 with A/C. works like a charm.

ProMan · #13 05-25-2005, 09:33 AM

Well, this looks like work fine. But I don't think the mechanic really found the problem. By increasing the idle rpm, it may look ok, but I believe this is not a real fix casue it's not the way the engine should work. The idle should be controlled by ECM and when the AC is on, the idle should be kept about the same.

I would suggest you to get a 2nd opinion from another mechanic and see if he can identify the real cause of low rpm. Or for the long run, you may experience some problems with your engine.

Good luck.

funky · #14 05-25-2005, 10:36 AM

thanks for the tip. by the way, why would you suspect a problem with the engine by just raising the idle up a hundred rpms? the car is actually smooth running now, i would think the shaking of the engine would have caused long term problems.

ProMan · #15 05-25-2005, 10:57 AM

Oh, it's just a huntch and a suggestion from my experience with cars and shops. I am not an expert on engines, just go by feelings. First, the idle rpm is not right at 850. It's correct at around 750 as you stated, so for your car it's not an idle problem. Second, the rpm should not drop when the AC is on. The engine should compensate the load and keep the rpm. What failed to compensate the load should be where the problem is located. So, adjust the idle may be a quick way to fix it, but I don't think high idle is good for the engine. Hey, just my guess. Don't be too worried about it.

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