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93 Nissan Sentra SE rough low idle
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HonganOs
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Mar 8, 2015, 4:22 AM
Post #1 of 9
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93 Nissan Sentra SE rough low idle
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'93 Sentra SE (GA16DE), California model. Only 66-67k miles, generally used only for short stop-and-go trips.
Problem: Once the car reaches operating temps, the idle is low (500-650) and somewhat rough. Not sure if there's a random misfire (never experienced one before), but there is a random sounding sort of light pop in the exhaust once it's warmed up.
So far I have done the following, in no particular order:
Disassembled and cleaned the IACV.
Replaced all of the small diameter vacuum lines. I figured that was a good idea after 20+ years anyway.
Cleaned MAF and tested per FSM. Looks good physically, and the resistance is within spec.
Cleaned throttle body and tested TPS per FSM. All clear there.
Removed and cleaned EGR valve and replaced EGR gasket. 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.
Replaced O2 sensor. Again, seemed like a good idea after 60k miles and 20 years.
Tested coolant temp sensor per FSM, but I only tested it cold. Checked out. Should probably test it at operating temp.
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.
Oil change, but I didn't expect that to make a difference.
New cap, rotor, plugs, and wires. (Duralast on the cap and rotor, NGK on the plugs and wires.)
Air filter's clean, only a few thousand miles on it.
Ran self-diagnostic on ECU and checked for codes. Only got a 55. All Clear.
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. That's a little higher than the +/-1.2% accuracy of my multimeter.
I might have done one or two more things, but my brain is fried at this point. If I think of anything else, I'll be sure to mention it.
Additional info:
The valve cover gasket sure looks like it's leaking. I'm sure I'll get around to it, but I don't plan to prioritize it over this problem. Unless, of course, it's contributing to the problem. I have no idea if that might be the case.
After all that, the problem persists. I'd say the idle is maybe a little smoother after all of those things were done, and it doesn't feel nearly as close to stalling as it did before, but the idle's still in that 500-650 range and bouncy. My current suspect is the coil. I'm thinking that once it gets up to operating temps, it's showing its age. But I'd love to hear any theories/suggestions you might have.
Thanks for reading, and sorry if I gave too much info.
(This post was edited by HonganOs on Mar 8, 2015, 4:23 AM)
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Mar 8, 2015, 5:30 AM
Post #2 of 9
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Re: 93 Nissan Sentra SE rough low idle
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Thoughts on older CA poke around car:
What did old plugs look like? Evenly worn or the same or one or more different? It helps to look at the old stuff.
Valve cover gasket? Can defeat integrity of PCV which needs to work properly.
IDK - CA fuels (sold there only) and the low poke around miles with no codes I might put some (don't use tons) Techron by name brand fuel solvent and take it for a good highway run.
If roughness is from leaking high voltage at a could it should react if you mist (not soak) it with a spray of water with some salt in it and maybe even show an arc jumping around?
Valve cover? Try just no more than nut driver tight see if it's loosened up some. Do NOT overtighten is the point so like "screwdriver tight" no more.
Maybe, maybe just would like a good run and burn up some fuel at speed and some load of hills and faster than usual take offs from a stop.
Ya - some cars really don't like constant poke around driving after lots of it,
T
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HonganOs
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Mar 8, 2015, 6:27 AM
Post #3 of 9
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Re: 93 Nissan Sentra SE rough low idle
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Great question about the old plugs. Meant to include that info. All four look pretty much exactly the same. The electrodes look dark, like they might be dry fouled, but the insulator still looks pretty white to me. But bear in mind that I replaced the plugs even though they had maybe 8k miles on them. Long story, but the short version is I let a mechanic do a tune up a couple of years ago, and he used Autolite plugs and Belden wires. I figured it was cheap enough that I might as well switch them out for Nissan's preferred NGK brand. Further, the gap on the old Autolites was a little below the bottom end of the FSM spec range when I pulled them out. Makes me think no one ever checked the gap in the first place.
Valve cover gasket and PCV. Yeah, that's what I figured. Maybe I should make that I higher priority. Also, thanks for the idea about just checking to make sure it's tightened down without going nuts and over-tightening.
Haven't used CA fuels in something like 30k miles. I moved across the country more than a decade ago. Techron and a highway run sounds like a pretty good idea, but I've read elsewhere that Nissan recommends against fuel additives of any sort. On the other hand, I've read others who've made the same recommendation as you. I suppose it couldn't hurt, especially not the freeway run.
Finally, I'll likely try the mist trick to look for leakage at the coil. I've read about that method elsewhere, but I wasn't sure it would apply to this particular set of circumstances.
Thanks for the tips, T. I really appreciate any help I can get on this one. I'll be sure to post any new information just in case anyone else is having the same problem.
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Discretesignals
Ultimate Carjunky
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Mar 8, 2015, 7:57 AM
Post #4 of 9
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Re: 93 Nissan Sentra SE rough low idle
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Is this engine misfiring? Low idle, popping out the exhaust, and rough running are all signs of a miss.
is there anyway you could record the sound of the engine when it is running rough then upload it to a media hosting site and then paste the link in here?
If the valve cover is leaking, is there any oil down in the spark plug wells? If oil gets on the plug wire boots they will swell up and allow secondary to leak out. Also inspect the plug boots themselves for spots that secondary may have been leaking out.
How does the engine run off idle?
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Mar 8, 2015, 8:06 AM)
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Tom Greenleaf
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Mar 8, 2015, 8:04 AM
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Re: 93 Nissan Sentra SE rough low idle
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Sounds like you are on top of many things about this. True - additives are NOT usually any kind of mechanic in a can thing and to be avoided but some actually can help with certain things. Most cause problems!
NGK - right move. Belden? Think there are different qualities on assorted brands what you want is OE spec stuff.
The PCV and valve cover are of interest along with the "popping" sound heard sometimes? Thinking on that and worry about too much or too little fuel delivered but plugs looked good and even which is a good sign.
Old phart here but some things don't change to close in on a problem. Intake manifold vacuum observed with a "T" in line can help with diagnosis for general compression, valve issues including valve timing either chair driven or belt you have to tell me which exact engine to look up - if a rubber cogged timing belt it really needs to be known how old or miles. IDK, most that fail it's all at once not a jumped tooth and real trouble with engines and valves on most!
OK - Fuels again. Damn ethanol isn't good for anything not specifically made to tolerate it! All states TMK suk with so called "gas" junkier than I've ever known of and a wild assortment of additives none of which age well or separate in just a couple months! Not good for much of anything.
I'd like to see manifold vacuum over 18Hg at idle and a smooth reading. It should spike over 20Hg with a no load snap or RPM up over 2,000 quickly. If not steady or floats around it's telling of what is likely without tearing into things too early best to know first. Less likely with this but check anyway. Hold RPM while watching vacuum at about 2,000 RPM and it should show same Hg reading as idle or suggests exhaust restriction somewhere not always a converter but would be first on most lists.
Let me us know on the valve cover gasket too. If you just snug those up and find they are like about not tightened at all when you get there they might have had a gasket put on or maybe OE that squished down and be fine or not with just what I mentioned. It matters as PCV is drawing in fumes creating a very slight vacuum or should be removing the gasses but if leaking air in thru valve cover or anywhere OR too much blow by it can't and the troubles begin.
If not abused or somehow sludged up this could be a good car for quite a bit longer,
T
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HonganOs
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Mar 8, 2015, 11:29 AM
Post #6 of 9
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Re: 93 Nissan Sentra SE rough low idle
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It's becoming increasingly obvious that I came to the right place. I can't thank you guys enough for the replies.
@Discretesigals: I think it's a misfire, but it's like I said. I can't recall ever dealing with a misfire before, so I'm really just guessing. I might be able to record it, but to speed things up I went to Youtube and found a video that's really close. Unfortunately, only about 7 seconds of it are relevant – from :50 to :57.
link removed ............ not allowed
Unlike the guy in the video, high idle on a cold start sounds fine to me. Smells rich, but sounds fine. But once it warms up, that video is pretty darned close to what I'm hearing, only on a different exhaust system. Just tested it, and it's worse in park. Put it in drive, foot on the brake, idle drops, and the irregularly timed “popping” becomes less obvious, though it's still there. Drives okay, but it seems like it's not accelerating quite as well as it should. Problem is I never paid that much attention until it became a problem, so I don't have a reliable basis of comparison. Doesn't smell rich to me once it's warmed up, either.
No oil in the wells, and I was sure to look as closely as I could when I swapped out the Autolites for NGKs. The old Belden boots looked fine to me. No swelling. However, there was a little burned oil on the old plug threads and nowhere else.
@T: After listening to that video, I'm pretty close to convinced there's a random misfire. If it was just one cylinder, there should be uneven wear on the plugs, right? I assume that's why you said even wear is a good sign. Or at least not a bad one.
Took your advice and checked the screws on valve cover. All of them were noticeably loose, one far more than the others. I tightened them down just barely hand tight (didn't want to go overboard), starting in the middle and alternating sides, as close to a star pattern as I could manage with the irregular placement of some of the screws. (BTW, I still can't get over phillips heads on a valve cover.) I assume this should/might help with any leakage, but I didn't hear any difference in the idle after I was done.
I'm thinking you're very likely right about T-ing in to test vacuum, but I don't have the equipment. I might know someone who does, but it will probably take a few days to get it...if I can get it at all. I suppose I might have to stop being cheap about this and pony up for the gauge.
Speaking of which, I borrowed a timing light, but it's the old school spring type. Never used one, and I'm hesitant to try for fear of arcing off that spring. I don't think it's a good idea to stick it in a plug well, and I'm not too sure going inline from the cap to the #1 wire is much better. Feel free to let me know your opinions.
Additional info: Forgot to mention that the mechanic who did the tune up also did an oil change...and over-filled the oil by about .6 quarts. Capacity is supposed to be 3.4 (including the filter), and I'm pretty sure he just dumped in 4 and called it a day. I didn't notice until the car started acting up, and that's when I changed the oil myself. Also noticed a thin film of oil on the butterfly plate when I cleaned the throttle body, which is why I replaced the PCV. I just assumed too much oil plus old PCV likely equals oil in the intake. All looks clean now.
Little more info that I didn't think was relevant until just now. I'll try to keep the story short. Maybe five years back I got tires and brakes. Brakes didn't feel right on the way home, which made sense because after I got home I noticed a puddle of brake fluid under my passenger-side rear tire. They had busted a brake line. Had them tow it back and fix it.
However, about a year and a half ago my brakes went out in traffic. I mean, I felt a snap in the brake pedal, and my foot slammed to the floor while the car kept right on moving at about 35mph. No collision, thankfully. That's what the e-brake and reflexes are for. I got out, checked under the hood, and one master cylinder stud was completely sheared off the booster, while the nut on the other was loose to the point of being halfway off. I'm not going to name names, and I'm not going to point fingers. I'll just say I took it to another mechanic who said the booster had to be replaced to fix the sheared stud. He put on an aftermarket booster (part# 160.88626). I mention all of these experiences for two reasons:
1. Is it possible that the diaphragm in the booster is causing a problem? I doubt it, because I tried pumping the brake a few times, built up some resistance, then started the engine. Pedal slid nice and easy to the floor. That, I think, means it's all good, but I'm not an expert. Still, I know the booster connects to vacuum, so I thought it might be relevant.
2. Those experiences are why I'm here after not working on a car in more than a dozen years. I've got some experience. Even did the head gasket (and much, much more) on my old 85 Sentra, but I've never worked on a fuel injected car. That said, I'd rather screw it up myself than pay someone to screw it up for me. Don't misunderstand. I am ABSOLUTELY NOT bad-mouthing mechanics at all. I know there are great mechanics, I knew a bunch of them personally during my brief stint in auto parts (20+ years ago), and it sure sounds like I'm talking to a couple of them. It's just that I haven't had good experiences lately, and I miss getting my hands dirty anyway.
Again, sorry to write a novel about this. I just believe more information is probably a good idea.
Thanks again!
(This post was edited by Hammer Time on Mar 8, 2015, 12:48 PM)
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Tom Greenleaf
Ultimate Carjunky
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Mar 8, 2015, 12:26 PM
Post #7 of 9
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Re: 93 Nissan Sentra SE rough low idle
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Our novels are making me dizzier than I already am! Handy tool for vacuum stuff...........
^^^^ Hope that shows,
Seems it did. Can get that or similar for about $30-$50 bucks, well worth it.
Called a hand vacuum pump w gauge has a "T" with a kit and a check valve + assorted stuff - handy thing plus plain gives vacuum readings. "T"ing in allows item(s) vacuum is supposed to go to keep going is the idea.
Brake booster is a sad story and no excuse to give a car back with stuff broken like that AT ALL never mind brakes! It's kinda ruled out as that now a while ago and was fixed but if booster is leaking it too is a vacuum leak. Plug it off to test but know it won't have power brakes and shouldn't need to drive for a test.
Same with hose to PCV - does that draw full manifold vacuum? It's larger hose so perhaps just go to source and plug it there and see if that changes anything and if hose is good still. Some for no reason can swell or collapse, leak -- just know it should be generic hose of that size marked as PCV, fuel, vacuum line -- type that doesn't collapse and tolerates oils and fuel sold by the foot.
Oil overfill by .6 shouldn't have been a problem. Where you get in trouble is when parked or running on a VERY steep slope with oil level not in range. My guess is that didn't cause anything?
Good for now on valve cover and keep an eye on it. Replace if needed and clean any oil dry with paper towels or something not wash it off with solvents/detergents and water - NO!
Stray high voltage even with new items. If wet it should make things really worse or see it in front of you arcing. OK - I'm balsy (don't do this) to just wet my hands and get shocked as if you are expecting that it doesn't freak you out but don't do that. Perhaps use a long screwdriver that is jumpered to ground and if you touch the right spot it would act up or arc then for you.
New items dammit can be bad too.
Keep checking and try to get this over with soon as now you mentioned power issues so it might be harming/plugging up converter and unnecessary but stuff happens and that costs bucks no way around it. Mentioned you can tell with vacuum gauge if so or loosen exhaust before it and engine to see if really suspect. It may be on the list now - damn!
T
(This post was edited by Tom Greenleaf on Mar 8, 2015, 12:27 PM)
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HonganOs
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Mar 9, 2015, 5:02 AM
Post #8 of 9
(1836 views)
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Re: 93 Nissan Sentra SE rough low idle
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Quick question, T. Can the type of vacuum tool you mentioned be used to test for exhaust restriction? Like, threaded into the O2 sensor socket? Or is that a completely different tool?
One short update. I tried the water mist test in the area of the distributor and coil. Sun wasn't up yet, completely dark in the garage, and I didn't see a thing. Maybe it's not a coil problem.
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Tom Greenleaf
Ultimate Carjunky
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Mar 9, 2015, 5:25 AM
Post #9 of 9
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Re: 93 Nissan Sentra SE rough low idle
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Vacuum testing: Yes it can show of an exhaust restriction but doesn't know where. Think I said you attach to actual manifold vacuum, read that # even on that pistol type shown. Now just hold idle up to 2,000 or a tad more RPM held and should be the same as at a good idle for vacuum. If restricted it would read lower.
That exact vacuum pump gauge combo is plain handy as said. Not just a gauge but it makes vacuum for testing assorted things too.
Know that actual manifold vacuum IS the info either converted to an electronic signal or direct to a device that indicates load on engine and what other adjustments it will make to run as well as it can. If either way that sends wrong info other adjustments would be confused and likely make more wrong adjustments,
T
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