Sentra GA16DE bouncy idle and coil specs

[HonganOs]

Please forgive me if I didn't manage to use the right search terms to find the answer to this question. I've been working on this for weeks, and my brain is pretty much fried at this point.

'93 Sentra SE (GA16DE), California model with a subtly bouncing low idle after reaching operating temp. (500-650 in drive is a little on the low side, right?) Only 67k miles, but...you know. It's old and only used for short stop-and-go trips.

I'm not sure I should waste your time with the list of things I've already tried, but I'll mention as many as I can remember in no particular order. Cleaned MAF and tested per FSM. All clear. Cleaned throttle body. Tested TPS per FSM. All clear. Cleaned EGR system, replaced EGR gasket and all of the vacuum lines I could find. I didn't test the EGR, because I don't have the equipment. Still, the diaphragm looks solid and doesn't appear stuck in either position. Cleaned IACV assembly. Replaced O2 sensor. Tested coolant temp sensor per FSM, but I only tested it cold. Checked out. Should probably test it at operating temp eventually. Used throttle body cleaner to check for vacuum leaks. No idea if I hit all the relevant areas, but I never heard a change in idle. Replaced fuel filter. Replaced PCV, but I didn't expect that to make a difference. Same with recent oil change. Recently picked up a new cap and rotor (Duralast, which I know isn't really the ideal choice, but I somehow doubt it's that's huge of a deal in the scheme of things). Air filter's clean, only a few thousand miles on it. Checked for codes on the ECU, got a 55. All Clear. After all that (and probably more) the idle's still a bit shaky, but it doesn't feel like it's going to stall anymore. Don't know if all of that was really necessary, but I went with the idea of doing the cheap stuff that probably needed to be done anyway.

Little more info. I made the mistake of letting a mechanic do a tuneup maybe 6k miles ago, and he used Belden wires and Autolite plugs. The plugs look to me like they've got some mild dry fouling going on, so I went ahead and ordered some NGK plugs (part# BKR5E-11, as I don't put enough miles on this thing to justify iridium) and wires (stock# 9889). What's more, the gap on the Autolites looked way too small, so I opened them up a bit to about .042.

But checking the plugs got me thinking. I tested the coil, and the primary was right on the money per the FSM – .9 (taking into account the resistance of the meter wires). But the spec for the secondary should be 13,000, and I got about 13,220 on a room temp coil. Could that be part of the problem? Or maybe the whole problem? The coil's just out of spec and needs replacing, and the situation only becomes apparent when the engine, and the coil along with it, starts to warm up?

Sorry if I babbled too much, and thanks for your patience if you got this far.

[frapjap]

Welcome to NICO!

It sounds like you really love your Sentra.
When the idle dips, does the engine try to stall? Any misfiring? (I'm guessing not).
Honestly, the only thing you might have left to do is to check the timing with a light. If its spot on, you can just chalk it up to being an older engine that you can enjoy for ages.

[HonganOs]

Thanks very much for the welcome!

Do I love my '93 Sentra? Well, let's put it this way. I was head-over-heels in love with my old '85 Sentra, and I really miss being a 20 year old who worked in an auto parts store. Also, I'm totally obsessive about problems I can't solve, and the only mechanic I trust around here is insanely expensive and charges for everything from diagnostics to "misc shop equipment." But yeah, I'm learning to love my '93. I just wish she'd be a little more cooperative.

Nope, it doesn't stall. It felt like it wanted to before I did the stuff I mentioned in my first post, but it smoothed out a little at a time as I did the jobs I listed.

As for a misfire, I'll be honest. I don't think so, but I'm not 100% sure. I've never experienced the condition myself, so I've never had to diagnose it. But I did a bunch of reading after you asked (great question, BTW). It feels and sounds a bit that way when idling at operating temps, but there haven't been any CEL's and it still accelerates just fine. So, if it's a random misfire problem, my ears are too inexperienced to know exactly what they're hearing. If that's what's going on, do you think plugs, wires, and/or a coil would correct it? Or maybe a vacuum leak I haven't tracked down?

Timing was going to be my last check after I replaced the plugs and wires, as I figured it would be a good idea after 60k anyway. Naturally, I don't have a timing light. Any suggestions as to a brand/model that won't break the bank, assuming the problem isn't handled by the NGK's?

Incidentally, I have one or two other questions, but they're unrelated to the idle problem. Would you prefer that I start new threads for those? Again, thanks for the welcome, Frapjap! This forum has been an invaluable resource.

[frapjap]

No worries man, we're glad to be here and to help others.
If you've got some unrelated other issues, post them up separately. But in case I miss them, just put a link here, too.

Good thinking about a potential vacuum leak. That test is cheap and easy to do. If you want to test for vacuum leaks, buy some carb or choke cleaner. Spray it around any/all vacuum lines or suspected vacuum lines. If you hear the engine rev up, investigate the area more closely to see if you can pinpoint the leak.

As for your diagnosis of the misfire- if you have one, you'd know it. Acceleration would be really poor and the engine would idle really, really badly. Its much more easy to detect a misfire in a 4 cylinder than a V6 or an V8.

However, if you're still wondering, there is a simple test you can do. While the engine is running, pull off the spark plug boot of each cylinder (one at any given time) and listen/watch for a difference in sound and how well the engine runs. When you remove a boot/wire that is operating correctly, the engine will run very poorly. If this happens, this will tell you that cylinder is working correctly and isn't the problem. If nothing changes, than that cylinder has a bad plug or wire. Repeat until you've pulled each cylinders plug wires one by one.

There are a few models of timing lights. You can spend about 30 bucks at harbor freight and get the type that clamp around the wire. http://www.harborfreight.com/timing-lig ... 40963.html
There is another style, but its a pain in the butt to use and you'll be happy you spent the extra $10.
Take a peek at the FSM link in my signature and check your year/make/model for the correct degree of timing. It should be in some of the first pages or be under "ignition timing."

[HonganOs]

Again, many thanks for the tips. All info is great appreciated.

Great to know that the misfire would be pretty obvious under acceleration. That condition isn't present, so I'll take it off the table for the time being. Might still try the plug pulling test, but only if the NGK wires and plugs don't take care of the problem.

Tried the carb cleaner test for vacuum leaks. I didn't hear anything change, so I'll set that aside, too.

As for the FSM, I managed to find a copy when this began, and I've been using it ever since. For anyone else who might need some help, Frapjap's right on the money. Take a look at his sig and study the FSM. It's an incredibly helpful reference for all sorts of specifications.

Timing light looks great, and the money's fine -- even for someone as cheap as I am. Thanks again!