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2001 sentra GXE idles like garbage, no check engine light

I have a 2001 sentra that appears to be running extremely rich. New spark plugs it runs great, give it a few days around town and they look like crap again and with that it bucks at speed off and on, idles like garbage.

Now for the storyand what’s been done. I got it in July, it ran like this then. After changing injectors, MAF sensor, and O2 sensors. Scan tools showed the above was bad. Now, there is no check engine light but it’s still running rich. We also found that the gas was tampered with, no clue with what but it was bad and not cleaning up. Because of that, I also replaced the tank and the unit in it with pump, filter, regulator, and suck in it. I got the tank from another car that’s known good after an extreme cleaning and the car it came from, with the old tank in it, cleaned well, runs perfect.

I’m running out of ideas, with new spark plugs, it runs perfect for a couple days then they get fowled, it looks like running very rich, on all 4 of them though one did look a little worse than the rest. Does anyone have any ideas what I should look at next? idle is right where it should be in RPM. I believe the AC compressor is locked but that shouldn’t have anything to do with it.

Other unrelated things I notice but maybe it means something to someone, the headlights dim and come back as if the alternator is going but that’s new, the concerning problem is not and voltage looks fine so far with a volt meter. AS I said AC compressor appears locked up but I just haven’t used the heat or anything yet so that’s not an issue. It also starts hard when the spark plugs get fowled but not with clean ones in there so I think that’s a result, not a cause. I think everything’s OK electrically, I want this fixed before winter sets in. Anyone have any ideas? I have another car ti pickparts from, I can’t register it at this time so I can pull parts off it to try but being an extremely active 1 car family I need this thing straightened out before something serious happens because of it. Thanks, John

This isn’t going to sound nice, but it needs to be said . . .

Right from the start, you should have paid somebody competent for a proper diagnosis and repair

From what you described, that is not at all what happened

Do yourself a favor and immediately stop throwing parts at the car. It’s not working, because whoever is doing the diagnostics, if you can even call it that, doesn’t know what they’re doing

Bring this car to a reputable independent shop for that proper diagnosis and repair, which I already mentioned

You said the scan tool said all those parts were bad . . . Not so. You clearly had a bunch of fault codes, which do NOT say “This part is bad, replace it.” The fault code is just a starting point in the diagnostic process.

From the sound of it, your fuel trims are extremely positive, but that’s not really the point right now

The point is this . . . whoever has been attempting to fix this car needs to stop and hand the reins over to a professional who knows what they’re doing

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It was a pro with the best reputation in town who changed the injectors, MAF sensor, and found the bad gas. He also told me to change the tank myself, which I did because it wasn’t worth the labor cost involved. It was another pro before I got the car who cross threaded 2 of the O2 sensors horrible, put the power steering belt on wrong and wrecked that belt, and I’d bet it went to him for the same thing I’m now dealing with.

I’m looking for help, not criticism, if that’s the best you can do is tell me to see a pro, I’d say you’re the one who has no clue what he’s doing and I’d thank you to not reply so those who actually want to help me reply and I don’t miss it in your crap. Likely I’ve been working on cars a lot longer than you and always figured it out, this is the only one I’ve struggled with and seen so many reports of this online. Before I throw away more money so a “pro” can keep throwing parts at it and my money, I’ll swap over the rest of the fuel system from the other car I have, same car, or the whole engine. I wish I could register the other car, it’s the better of the 2 but I can’t.

Even though irlandes and I have our disagreements from time to time :stuck_out_tongue_winking_eye: this is one case where I have to wholeheartedly agree with him

This is exactly what he’s always talking about . . . if you bring your car to the wrong guy(s) or the wrong shop(s) it’s going to get very expensive and very ugly

I apologize for nothing, because there’s nothing to apologize for

I hit the nail on the head . . . if that’s not the kind of answer that was sought, so be it

In a perverse way, I agree with OP in one regard . . . that he used the term “pro” with parentheses

But apparently I have no clue what I’m doing, as per OP :laughing:

That actually made my day and put a smile on my face, as I’m typing this :slight_smile:

I’ll leave this thread to the other regulars . . . you can have it :wink:

I’m sure you didn’t laugh as hard as I did when you said the same of me. I’ll ask again, if you’re not going to post a response that has to do with actually helping me fix this car, can you not bother replying at all? I did not come to a board looking for help fixing it myself to be told take it to a mechanic I can’t afford and don’t trust to fix the problem. It’s my experience the number of mechanics you can trust can be counted on one hand with fingers left over.

Making insulting remarks about mechanics is probably not the best way to receive answers . This forum has quite a few really well versed mechanics who can only use descriptions provided.


I was refering to my experience so far. My family has been screwed by
many mechanics and I know many people in every field around my area
are not trust worthy. That’s why I do everything I can myself and if I
need help I try to go out of my area to ask for it. Sadly I’m not sure
there is anyone who can actually help me with this situation based on
response so far. At least it didn’t cost me anything to ask, I’m sick
and tired of throwing money at it to have it improve a little but not
a lot and still have spark plugs look like crap in a week. At least no
codes come up on a scan anymore, that’s progress. I’ll either keep
throwing stuff at it since no one else knows what to tell me or start
putting my money in to registering the other one.

Fuel pressure regulator failed…

The flip side to the all mechanics are crooks argument is that there is a certain segment of customers whose cars are best not touched…

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I thought the fuel regulator is in the tank in this car so was swapped
with the tank. Is there another one in the fuel rale?

If it’s on the fuel rail, it should be easy to see.

Here’s what the fuel pressure regulator looks like.

Remove the vacuum hose, and if gas leaks out, replace the regulator.


It’s not obvious on either car. Looking online, some say there is one, some say there isn’t. I don’t know if that has to do with the CA emissions verses not or what, there is so much misinformation on the internet when it comes to these cars, or conflicting info.

I see it, I’ll give that a shot.

In looking close on both cars, I see nothing at all like this on the fuel rale. I dont’ even see any difference in the 2 like one’s different from the other or anything.

This is a drawing of the fuel rail, the fuel pressure regulator is top left in the drawing, passenger side on the vehicle.

OK, somewhere I got the idea it was on the other end of the fuel rale. I found it and no fuel in the vacuum line. A little Oder of gas but none physically comes out and if I disconnect the vacuum line while it’s running it runs about the same if not the same. There is vacuum though at that line. I’m not so sure that hasn’t been worked with or replaced before though, on the other car there are rusty security screws on it. On this car I’m working on, they’re Philips as is about everything under that hood and the fitting for the vacuum line is very clean.

First off, have a fuel trim measurement done. This is needed to confirm it is actually running rich. Fouled spark plugs could be caused by other problems too.

What does the inside of the end of the tailpipe look and feel like? Gritty sand-like carbon deposits? Does it feel greasy at all?

This problem could be caused by a faulty pcv system aslo. So double check that. Might be a good idea to just replace the pcv valve, see if it helps. Inexpensive.

If it is proved to be running rich, rich operation is most often caused by vacuum or exhaust leaks. Check all the vacuum hoses, especially where they connect to something. Next check all the vacuum operated devices that they hold vacuum, especially the brake booster, which is a common vacuum leak source. And check the entire exhaust system for leaks. And for leaks in the intake air path, usually there’s an accordion like boot between the engine air filter box and the throttle body. That all has to be air tight.

Edit: Please clarify. Your tag says “Toyota” but you say in the OP it is a Sentra. That’s a Nissan, right?

I just noticed it says Toyota, I don’t know why. It is a Nissan though, I’ll have to see if I can change that.

Exhaust is good, no leaks and actually looks normal as far as I can tell at the tail pipe but I’ll double check in the morning. Vacuum system looks OK, I’ll check it closer tomorrow though and see for sure. The accordion from the air box to throttle body is fine, not cracked, dried out or anything.

The spark plugs look like it’s still running rich but if something else can make them look exactly the same, maybe I should check in to it. Reason I say that is, these cold New England mornings, when you start any car cold, it smells rich. This one doesn’t. When I first got it and had the codes, it did, black smoke, the whole 9 yards. Exhaust looks and seems normal other than that, it’s getting through to the tail pipe so there’s no blockage anywhere. It doesn’t smell rich on these cold mornings though and that’s confused me too, especially where the unregistered 2000 one does as I would expect it to. I checked the PCV valve a couple months ago, no signs of anything with it but true, it’s cheap and looks easy, no reason not to just change it and eliminate that possibility.


This past summer I had a lean/high idle speed problem w/my truck that was caused by a faulty pcv valve. So they do go bad sometimes. Another idea, oil getting past the piston rings or the valve stem guides can foul spark plugs. Do you seem to be using an abnormal amount of oil? More than one quart per 1000 miles? Concur, it is sort of unusual you aren’t noticing a gasoline odor on the first cold start of the day. I have always noticed that on my Corolla, which I presume to be normal operation. Sort of opposite of what you’d expect for a rich condition, but may be some kind of clue to what’s happening anyway. If you only have time to check one quick thing, check to make sure the brake vacuum booster is holding vacuum to 20 inches. Requires an inexpensive hand held vacuum pump w/gauge. Best of luck.

Well, nothing’s open to get a gauge today but the old check of , pump the peddle hold it and start the engine, the peddle does go down when it starts so in that way it looks good. I can’t get a gauge to really check for sure until tomorrow. It’s not losing any oil at all, it’s been at the full line for 2000 miles, 4 months, it hasn’t dropped at all. From my experienced the plugs look like charcoal, not oil fowled but the lack of smell on cold start is starting to make me really wonder. Idle is in range it should be for RPMs but just rough though I was noticing last night it a little up and down, maybe fluctuating 100 rpms or so, not drastic , I’d expect a drop like that when it’s at its roughest though.