So I’m driving to the airport for Christmas when I notice the car is idling high - not that unusual, it’s pretty cold out and I really didn’t give the car five minutes to warm up. But as I get closer to the airport I notice the red battery light flickering on. Not steady, but a flash now and then. I then took the car out of gear and coasted a bit. This time the idle was high, but when it would get to about 1800 rpm it would quickly jump back down to 1000 or so. The car did this repeatedly… kind of freaked me out.
On the way back a week later (it’s about 15 degrees warmer in Boston than it was two weeks ago) the light has not re-lit itself but the weird idling thing happened when I was in bumper-to-bumper traffic on I-93.
What might this be? I haven’t had a tune up in about a year, but I drive perhaps 3000 miles a year… could it be time already?
You may have developed a bad ground, probably the engine block to frame. It is causing your voltage regulator to freak out, which trips the battery charge indicator, and the computer is getting bad sensor readings. I would suspect corrosion and check both ends of your battery cables, and maybe have all the ground strap bolts checked and tightened.
I had something similar happen on a Mitsubishi automatic a few years ago and ignored it because it was intermittent. One day on the freeway the revs shot way way up and the engine just died. It was some part of the electronics system called “the unit” I believe. My mechanic, a very honest guy, told me I had been foolish to ignore it.
While it could be a voltage isue (and I would for sure do a complete charging system check first), it could also be an idle air control valve (IACV) that is sticking and hanging high.
Joey P - the tachometer measures RPMs, right? The two correspond.
I think I’ll scrub the battery posts and see if that makes a difference. It’s probably time for a tune up so that’s on the calendar as well. Thanks for the advice all!
If by tune up you mean spark plug replacement, the service interval is at least 30,000 miles. If it was done last year and you only drive 3,000 miles a year, you’ve got a life left on them.
Tachometers can act strange when the battery is going bad. When it happened to me, the tach needle jumped but the engine speed didn’t actually change. In my case, I had a bad cell in the battery.
That’s why I asked.
I had a friend who’s speedo (coulda been the tachometer but I don’t think it was) would just down to zero and back up. He took it in and they told him his transmission cap was loose. I never knew it could do that. Anyways, I asked because if the tacho and the RPM’s arn’t the same then the problem is with the tacho and not the engine (well not as much anyways), ya gotta know these things, you can’t make assumtions when diagnosing a car over the internet. It’s just soooo much harder when you’re not there to hear/feel/smell etc…
Yeah, I was on the highway once when the speedometer dropped to zero even though I was still moving along. It was a wire loose down behind the engine (sorry I can’t be more specific–the mechanic said he had seen it before and it would have affected the headlights if I had been driving at night :eek: )