Question: Higher idle after spark plug replacement

[thornburg]

Originally Posted by dkjones96

It's possible for this to happen. The more efficient combustion from the new parts can cause the engine to run a little higher at idle.

We get this at work all the time on older carbbed engines and notice that the IACV closes a little more at idle. If you have a EFI you should take a look at your IACV to make sure it's working correctly.

There don't seem to be any directions relating to the IACV on autozone's onine manual... I haven't checked my Hanes yet. Where do I find it, and how do I check it?

Jay2TheRescue: Perhaps I'll see if I can borrow a timing light... I looked at the timing procedure, and it looks like I don't need to take off the timing cover. It mentions (if necessary) loosening the "pinch bolts" on the distributor and twisting it to adjust the timing... The pinch bolts aren't regular screws, are they? I'll have to figure out what those are... The stupid autozone manual only has pictures of what it wants to have pictures of, and the haynes book has only a few pictures and they are mostly of different engines than mine.

[Jay2TheRescue]

Originally Posted by thornburg

There don't seem to be any directions relating to the IACV on autozone's onine manual... I haven't checked my Hanes yet. Where do I find it, and how do I check it?

Jay2TheRescue: Perhaps I'll see if I can borrow a timing light... I looked at the timing procedure, and it looks like I don't need to take off the timing cover. It mentions (if necessary) loosening the "pinch bolts" on the distributor and twisting it to adjust the timing... The pinch bolts aren't regular screws, are they? I'll have to figure out what those are... The stupid autozone manual only has pictures of what it wants to have pictures of, and the haynes book has only a few pictures and they are mostly of different engines than mine.

Its usually a bolt with a U shaped bracket that clamps down on the distributor to keep it from shifting. On most cars you can't get straight at it. You will probably need a distributor wrench to get at it. They are cheap and available at any parts store. A good thing to have if you plan on working on your own cars.

-Jay

[guest001]

well, just a little theory. advancing the timing increases rpm. If your cap, rotor, plugs, wires where all out of spec/worn or one or two where in not so great condition, I could see a slight increase in rpm after bring all these components back up to new condition. less resistence, technically the spark would fire sooner. increasing the rpm as if you increased timing. Interesting though, I've never really seen this, but it makes sense.

[thornburg]

I couldn't get any time to look at the car last night, but I did have an idea this morning...

The car was a little hard to start this morning (didn't take more than one try, but it cranked longer than usual before starting, and sounded a little different). Last night, I filled up at the gas station a little less than a mile from my house, so the car was started, and then not run for very long.

What if my battery is dying? If the battery is toast, that would cause the alternator to run more, right? Would that increase idle RPM? I'm building a house of cards here, since I know very little about cars/engines...

I have no idea how old the battery is. The positive terminal was all covered in crud, so I cleaned it & the connector with a wire brush while I had the battery out for the distributor cap.

[Jay2TheRescue]

Originally Posted by thornburg

I couldn't get any time to look at the car last night, but I did have an idea this morning...

The car was a little hard to start this morning (didn't take more than one try, but it cranked longer than usual before starting, and sounded a little different). Last night, I filled up at the gas station a little less than a mile from my house, so the car was started, and then not run for very long.

What if my battery is dying? If the battery is toast, that would cause the alternator to run more, right? Would that increase idle RPM? I'm building a house of cards here, since I know very little about cars/engines...

I have no idea how old the battery is. The positive terminal was all covered in crud, so I cleaned it & the connector with a wire brush while I had the battery out for the distributor cap.

How old is the battery? I don't think this is your problem though. Have you considered the possibility that you got a bad tank of fuel? Maybe there was some water in the tanks at the station.

-Jay

[kamesama980]

I'd get the battery tested, most shops and parts stores will do it for free. if they say it's bad, get a new one.

Other than that, I wouldn't worry about it, especially only 90 rpm. It's probably that with all your new parts your car has the power to idle higher with a load (IE: in gear, foot on brake). Hell, my truck varies +/-100 rpm just from a mildly dirty IACV.

[guest001]

load test without a vat 40 ;-)

[Ford Man]

Harder starting and/or rough idleing could be another sign of a vacuum leak. I don't think the battery would be an issue in this, but I guess anything is possible. Does your car have an idle speed control motor or idle air control valve? I have had them go bad before and the engine idle would change, but if that was the problem your ECU should be sending a code.

[Jay2TheRescue]

Originally Posted by Ford Man

Harder starting and/or rough idleing could be another sign of a vacuum leak. I don't think the battery would be an issue in this, but I guess anything is possible. Does your car have an idle speed control motor or idle air control valve? I have had them go bad before and the engine idle would change, but if that was the problem your ECU should be sending a code.

I remember years ago following my grandfather to the dealer to get his Grand Marquis worked on. It barely ran, was hard to start, and idled like crap. yeah the car was 8 years old, but only had 40,00 miles on it. The dealer called back a few hours later. The problem: a $0.89 vacuum tee had fatigued and snapped. They replaced it, and charged him an hour for diagnostic services and labor. The car ran great after that.

[thornburg]

Thanks for all these tips. I should have some time tomorrow night and/or Friday to actually look into it.