Trouble Starting and Rough Idle on Start Up



I have a 2005 Nissan Sentra with 74,000 miles on it, and it has had trouble starting for 2 or 3 years. When it started, I would turn the key and the car would almost, but not quite, start, and simply turning it off and trying again would work immediately. I had the battery replaced and the spark plugs at ~50,000 miles to no avail. About a month ago, I started my car and it had a really rough idle for about 15 - 30 seconds and the check engine light came on (registered an emission issue), but it ran fine. I had to get a routine oil change and emissions test anyway and they checked the spark plugs as a first measure. They all had some wear, but one was almost worn down to nothing, which the mechanic said was a result of the spark plugs (autolites?) so they replaced them with the Nissan recommended NGK kind. The next day my car didn’t start the first immediately, but on second try worked. A week later I noticed my car sometimes rumbling on idle right after start again, so they replaced the fuel filter and the fuel pump. Didn’t work, I still have a rumble about 30% of the time when I start, and just two days ago the check engine light came back on (I haven’t had time to get it diagnosed yet). Without knowing much about cars, it feels like the engine isn’t getting enough fuel or something. Could it be dirty/clogged fuel injectors? Should I be worried that my spark plugs were worn down after just 25,000 miles?

Sorry that explanation is a little long, thanks in advance for any help!


No, a spark plug shouldn’t be worn to the nub after 25,000 miles. Something is amiss there. Autolite makes a good spark plug. The problem, if there was one associated with the Autolite, is that that Autolite specific part number may not be recommended for your car. Its also possible is was a sample defect since the other plugs were ok. First thing, double check that Autolite part number is in the list of acceptable spark plugs per your car’s owner’s manual. Besides that, it would just be a guessing game until you’ve had the DTC codes read and posted them here. It wouldn’t be at all unusual that an emissions code would also cause the symptoms you are having.


If the Autolites were regular copper core plugs it’s possible they could be worn in 25k miles but one being worn down to nothing as it’s described would be a concern and possibly point to something else doing the plug in. This is all assuming the condition has not been exaggerated.

Erratic fuel injector or air leak affecting that cylinder could do a plug in. About all I would suggest at this point is at least get the codes pulled and see what the CEL is all about. The chain type parts houses such as AutoZone will do this for you free except in CA and Hawaii I think it is.

At the time of the plug change to NGKs, my personal preference would have been to run a vacuum test, compression test, and fuel pressure test; all basic procedures that are easy to do.
Everyone has their own methodogy but the spark plugs are out; the compression/vacuum test is another 5 minutes and could answer some questions.


I will try to hit the AutoZone tonight after work and post an update when I do. The mechanic did do a fuel pressure check and found it was a little low, hence the new fuel pump. I don’t know about vacuum/compression checks, though. I can’t remember the exact part number for the Autolite plugs, but they were the “acceptable” list, but just not the best choice (again according to the mechanic).

Thanks for the responses.


fyi to OP, I use the NGK plug recommended by Toyota for my early 90’s Corolla and never had an ounce of difficulty. I change them out at 30K, and they look practically good as new when I pull them, except that the gap has widened slightly, but still within Toyota specs. It’s a very inexpensive plug, I get them for about $2 each. Sometimes I do have to order them from the warehouse though, as the retail parts store doesn’t keep a lot of them on hand.

Sometimes mechanics will put in a different than recommended plug b/c it is claimed to be almost the same, and the recommended one they’d have to order and wait for it. But me, I only use the exact part number recommended by Toyota. If I have to wait a week to get it, then I wait a week. I figure when I purchased the car, I paid the guy who figured out which spark plug was best for my make/model/year, so since I paid him, I might as well follow his advice.

The combination of difficult to start and one plug – and only one – being worn to the nub makes me think, like @ok4450 mentions above, you may have a leaking injector. The fuel rail is sort of like a balloon. The fuel pump inflates it when the engine is running, and it is supposed to stay inflated, even when you turn the engine off. When you turn the key off, the fuel pressure is supposed to remain at around 35 psi for most cars. And stay at 35 psi for days on end, so when you start the car the next time, there’s plenty of pressure to inject the gas needed to start the engine. There’s two common ways the rail can loose pressure. One is through the fuel pump check valve, in which case the fuel goes back into the tank. That would make it hard to start, but would affect all the cylinders, not just one. The other is if the fuel injector leaks b/c it is stuck slightly open. Then all the rail gasoline leaks into that particular cylinder. The car would then be hard to start b/c the fuel rail pressure was low on the next start, and that particular cylinder with the leaking injector would be running rich, which could well burn the spark plug over time.


Hmmm…thanks for the explanation. It sounds like I need to get my fuel injectors looked at, or at least its a leading candidate. I also had my “service engine soon” code read at AutoZone last night, it was P0304 - Misfire.


“Misfire” means the computer expected the spark plug (no 4 in this case) to ignite the gas in the cylinder at a specific time in the cycle, and the resulting explosion to thrust the crankshaft forward with a certain amount of force, speeding up the rotation a bit, but when the computer measured how fast the crankshaft actually turned, it measured that the explosion didn’t happen for some reason, and the crankshaft actually slowed down instead of speeding up. That could definitely cause hard starting, rough idling, and poor engine performance. Esp on a 4 cylinder engine.

It’s possible a leaking injector could cause this, or an injector that wasn’t injecting like it should, as well as some other things, like a bad or clogged spark plug, bad spark plug wire, ignition system problem, etc. It could well be an emission issue too, as misfiring can result in high HC’s or NO’s. You might want to take a look at this link for some ideas. At the minimum, make sure your mechanic does a careful visual inspection of the high voltage wires and spark plug connector and spark plug for no 4. Any insulation cracking or signs of carbon tracks, good idea to replace the problem part. The no 4 injector remains suspect too. Best of luck.


The 304 is a misfire on cylinder No. 4 and while a 74k miles Nissan should not have compression low enough to create at problem it’s also a distinct possibility.
That’s why the mention of a compression test while the spark plugs are out.

A misfire on that cylinder could be spark plug, coil (COP), fuel injector, injector or coil wiring (not likely), or low compression.

If a compression test is run you should expect in the 180 PSI, give or take a bit, on all cylinders.


The plug that was worn down, was the tip really clean? Did it look like it had just been sand blasted or something, no carbon build up, no brown deposits?

Are you losing any coolant?


I got all the spark plugs back, and they were definitely worn and somewhat dirty. I haven’t noticed any leaks and that’s something I usually watch for. I dropped my car off at the mechanic this morning so they’ll run some diagnostics. Thanks for the posts, now I’ll have some idea of what I should expect.


So the mechanic had my car all weekend and said it started up and drove perfectly every time. They ran some more tests this morning and it tested fine. So, after all that he said he was going to switch the coil from cylinder #4 to cylinder #1, then if the CEL comes back on he’ll have a better idea of what caused the misfire. Seems reasonable to me.

I did put a bottle of water remover and fuel injector cleaner during my last fill up before I took my car in, but I find it hard to believe that would completely fix the problem. Especially since I’ve only gone about 15 miles on that tank.