Undercurrent

My car's behaving kind of wierd and I was wondering if anybody has any insight into what's causing this behaviour:

When it idles with just the engine going, it idles fine and the tach reads about 750 rpm, but if I have the A/C going, it oscillates between 700 and 800 rpm about once a second. 700 is (I speculate) near the stall point for the engine, so there's a little shaking at the bottom of the cycle, and then it bounces back to 800.

So, does this strike anyone as a "holy living fuck, the next time you turn the key it'll blow up" problem, or a "what the fuck are you doing bothering us with this trivial shit" problem? Right now I'm looking at it as a "<quizzical grunt> That's probably not supposed to do that" problem.

keyser_soze

Make, model, engine type, aspirated or injected, etc...We really need to know more. But no, it does not sound like an immediate problem. Is this at first startup, does it do it when it is cold, or warm, when it's been running a while, only at night, etc...We need a tone more info.

echidna

Most motors will automatically increase the idle speed (via the carburetion system), to adjust for the increased load. If it's an oldish car then it sounds like it just needs a tuneup / service, manually tweaking the idle speed would be the crude quick-fix.

Not too much to worry about though, just the annoyance of the occasional stall when cold. Lightly rev it in neutral at the lights to prevent this if necessary.

Evangelion

If you have the a/c on, you can expect some variation in the idle speed (the a/c is pretty demanding), so don't freak out if the needle takes a jump.

But if there's a bit of bounce between idle speeds, you might want to check your timing. Could be due for a tune-up.

Thor Q. Mada

Your stationary is a bit low. Just get it up a bit to 900 or even 1000 and she will do fine. The ac starting gives quite a sudden load increase to an engine. But a few more details as indicated by the others might be handy . Also, have you tried praying??

Evangelion

Actually, I'm a bit disturbed that all our suggestions so far have been so reasonable. It's not like guys to be realistic about cars.

We need someone to insist that he needs a nitrous kit!

Godless Dave

There's no poll option for "something minor that should be fixed soon". Minor problems have a tendency to turn into major ones if left alone too long. (If I had replaced my cylinder head when I still only had a minor oil leak I would have saved at least $125, the cost of a tow). But it sounds to me like you just need a tune-up. If you don't know already, you should get a maintenance tune-up every 30K miles and a full tune-up every 60K.

Undercurrent

Thanx for thr the replies. It is a fairly new car (2001 Saturn SC1) and has just been in for its 30000 mile service. I pointed out this thing to them, and they said that they'd have to take my car apart to access all of the sensors for a diagnostic without even listening to my description of the problem (and since the dealership is in Albuquerque and my apartment is in Santa Fe, leaving my car there overnight on short notice is not really an option). Irritated the fuck out of me, since I figured knowing what the problem is would at least narrow the search somewhat.

I certainly wouldn't mind a little bounce in the tach when the AC goes on -- resonable to expect that when you add a load to the engine, it takes a bit to adjust. But the oscillations never damp down, just 700, nearly stall, 800, 700, nearly stall, 800, 700, nearly stall, 800, 700, &c until the light goes green.

So where can I get a nitrous kit for a saturn, anyway?

Godless Dave

Try a mechanic other than the dealer. Some Saturn dealerships have great service departments and some don't.

Saturnspeed.com

Daggah

Depends on the car. My car's idle speed is ~750 RPM normally too.