rough idle


Asked by May 02, 2012 at 12:31 PM about the 1999 Infiniti Q45 4 Dr Touring Sedan

Question type: Maintenance & Repair

I have a rough idle, which doesn't seem to affect acceleration (yet), but it is annoying as heck.  No codes are thrown.

24 Answers


Need more information than what you gave. Like milleage? There can be several problems. Spark Plugs, Timing belt and others!!

2 out of 2 people think this is helpful.

Here are some questions that will help trouble-shoot your car. Is the roughness worse when cold? Is the engine smoother when driving? How does it start when hot? How does it start when cold?

5 out of 5 people think this is helpful.

Rough idle/misfiring is the Q45's Black Plague. It's probably the most experienced issue with the majority of them that have higher mileage. Mine's been misfiring and driving like absolute garbage for a year now and I've replaced almost EVERYTHING I think would even have the slightest influence on driveability. Depending on your specific answers to the other questions asked above, replacing ALL EIGHT coil packs seems to fix a majority of Q's rough idle problem. It did not fix mine unfortunately, but PLEASE keep us updated if you solve the problem! Thousands of Q45 owner's are suffering from the same issue! cheers

5 out of 5 people think this is helpful.
Best Answer

SInce I last wrote.. the misfiring steadily increased until it coded... P0300 I brought it to a Nissan dealership (no infiniti dealership near my home). They discovered non-platinum plugs and separated me from a few bills in exchange for new plugs.. the code disappeared, but the rough idle comes and goes now. I've had it now for over a month... and can reply to above: -Mileage is low 72,000! -misfiring comes and goes in waves.. no correlation with engine temp. -I opted out of an extended warranty option when I purchased it... so I now wish I had taken them up on it... -I ran a can of STP fuel line cleaner, the car seemed to idle better, but I cant rule out the placebo effect here. -I may premptively swap out all eight coils.. any suggestions on a supplier? -is this this something best done by an infiniti shop, or is a competent nissan service shop ok? Thanks

9 out of 9 people think this is helpful.

I have run into this problem on my Jaguar. What I found, when a plug fouled out, the coil went out as well. Another thing to check is your timing belts, as that is also known to cause timing to be off some. Platuim plugs are not necessary, but are the best for long term useage (most 100,000miles), and yes more pricey. Your mileage says it is time to check the timing belts anyway. Any auto shopo with a good reputation cqan check your problrm out such as one that advertises to be ASE certified. But, I would take the car back to the dealer that did the work, and request they check it out as they did not do the work correctly to eliminate the problem. They should check for warranty on the job they just did.

1 out of 1 people think this is helpful.

Hi all, my Q45 with only 68,000 original miles coded yet again... this time a misfire on cyliner 2. The service tech swapped in a coil from another car, and the misfire went away. After careful reflection, I gave the go ahead to replace all coils.. OUCH. After 3 days of driving, and accumulating 200+ miles, there is no sign of misfire/idle issues. Thanks to all for your help.

4 out of 4 people think this is helpful.

Was glad to hear your buzz'n along now. The coils are so sensitive that a mis fire from a plug. wipes out the coil as well at times.

1 out of 1 people think this is helpful.

The Nissan VH41DE engine in the Q45 should NOT be fed platinum plugs. Not all cars run well with platinum plugs. Every time I changed something on mine in the effort to fix my misfiring issue, I replaced the plugs. I've been through at least 15 sets of plugs in the last 2 years ranging from copper to platinum plus four and everything in and around that. Copper is required per the manufacturer and I can vouch for that because the car runs considerably worse with platinum plugs. Not sure why but probably something to do with the igniting temp. Glad coils fixed your problem! I'm still at a loss with mine and the dealer could not figure it our either so I'm going to replace all O2 sensors, both Knock sensors and both catalytic converters (maybe they are clogged). If that doesn't work then I'll have to find a new car to play with : (

1 out of 1 people think this is helpful.

By the way, what did the Nissan dealer charge you to replace the coils if you don't mind my asking? I went with used coils, maybe that's why replacing them did not fix my issue? Infiniti dealer wanted $1200 JUST FOR THE COILS themselves and putting them in myself!!!


Paul: I got a set coils for my Jag for $125.00 on Ebay. Yes dealers take advantage of consumers and our Gov. lets them get away with it. The right bank was the worst too get to, but new Platuim plugs & coils made it run like new.

1 out of 1 people think this is helpful.

Paul: You will know when your catalytic converters clogged. Your car will buck and loose power as the exhaust can not excape fast enough. I already had this experience, so this is not a miss. It does not make a difference what type of plugs are installed. The heat range DOES. Thats why there all different numbers on the plugs, which tell the heat range as well as the plug reach. Always check the gaping on your new plugs. The machine that gaps the plugs needs a break once in a while, and may malfunction at it's job.

2 out of 2 people think this is helpful.

Hi Paul, The total bill coils, diagnoses and installation was $1200. Yes, that sucked, but I had no other choice.. I'm not mechanically inclined, nor did I want to take a risk of further damaging things. SO far, idling and running smoothly.


I was a mechanic, that's the only reason I can do the work on my Q myself. It was a wise idea for you to go to the dealer for sure for the simple fact that if something went wrong or broke, they will back it up. wb6epp: That's a good point, my next project involves replacing the two downstream O2s and knock sensors and a friend of mine also suggested my cats are clogged so I'm going to have to do some research on whether or not removing the cats altogether will affect the sensor readings significantly or if I will have to buy and weld in new cats : /

1 out of 1 people think this is helpful.

To fix the misfire is simple once you change the plugs and coils..the sluggish comes from the AIRFLOW SENSOR..change it and I bet it run like a problem is the idling..I can hit the gas and get full power I jus want the idle to stop

3 out of 3 people think this is helpful.

Another update: I've decided to get rid of my Q. I really don't want to because the odds of finding another in the future that looks as good as mine here in Detroit are slim to none. As Gada said, i replacing the Mass Air Flor sensor may help. I took mine to the dealer as a last ditch effort before I decide to sell or keep her. They couldn't figure out what theissue was without just throwing massive money at it replacing random things and hoping for a fix. They did however drop my Mass Airflow sensor (at least I speculate they did) it ran worse when I got it back so I ordered a new one and the problem slowely got better as the ECU adjusted to the new sensor. Now almost 6 months later I'm experiencing the aftermath of the misfiring. The misfiring cylinders must have caused unburned fuel to exit via exhaust. I started getting o2 sensor codes and the exhaust started developing misc. Holes and leaks. Soon the car started running worse then when it was misfiring like ten fold to the point where its virtually not driveable anymore. Then one day another exhaust hole developed and I looked underneath to discover one of the pre-catalytic converter o2 sensors had been blown OUT OF the exhaust pipe bung and all still attached!! Never seen or even heard of that happening on ANY car in my life. Thanks to the misfiring sending the unburned fuel through the exhaust and catalytic converters, it burned out the cat converters and plugged one of them. I have not cut them out yet to verify that's what ACTUALLY happened but I'm 99% sure that's what it is and I decided to get rid of the car instead since gas mileage was reduced to around 8 mpg once clogged obviously. Hopefully someone can use this to their advantage before suffering severe consequences. I REALLY don't want to sell the car because I love it but I already bought a new car so...

3 out of 3 people think this is helpful.

I have a 94 q45 n it seems 2 have all the power. When I mash the gas it goes no where. When i say no where meaning ittakes awhile 2 cstch speed . Its been sittn for bout 4yrs has 130, thousand miles

2 out of 2 people think this is helpful.

hello My 1999 Q45 had plenty of power just a slight miss a idle changed plugs at ac delco got better then worse check inginition with 3 different scopes all said no iginition misfire so changed to ngk seemed ok drove 300 mile road trip now has really bad misfire at idle then checked the forums was suggested to use a in injector cleaner one was royal purple I went to Advance in Atalanta did not have that one so I found one came in a box was 18.00 said will fix misfire 100% among other things after about 100 miles no misfire that was a month ago car had 3 tanks a gas since, runs perfect still

2 out of 2 people think this is helpful.

2000 Q45 misfiring at idle .. worse when ac is on .. bucking and jerking occasionally .. .. don't know what to do .. mass airflow is good has new plugs from dealer ... thinking coils . But coils shouldn't make it buck and jerking .. help me please

10 out of 10 people think this is helpful.

I have a 1997 Infiniti Q45 that I bought off of my buddy for dirt cheap . He had problems with it and put way to much money into it trying to solve the problem . He replaced a whole lot of stuff and still seemed to have a problem . Engine rocked back and forth when I bought it off of him and the car was struggling to get over 40mph . I got a code to replace the ignition coils so I went and replaced all eight . After replacing the coils , my engine became a lot stronger and had no problem going over 40mph . The engine still shakes but not as bad as before . Now I'm getting another code that ignition 1 is misfiring . I pulled out a coil from ignition 3 and put it in ignition 1 to make sure it's not the coil so I Forsure know it's ignition 1 that's causing my car to misfire . Any other suggestions I should try ? I don't know to much about cars and I'm slowly learning . Anything will help . Thanks y'all .

I also have a 97 q45t - 260k miles. Never had to replace a coil. Still runs great. The issues I have encountered causing rough idle and running are (1)MAF sensor- clean, then replace (2)using non-NGK platinum plugs (ran like shit) (3)injector(s) gummed up after sitting for a month - injector cleaner cleared it up. (4)knock sensor - will throw appropriate code if the problem - make sure cable is still good (5) leaking vacuum or egr hoses - 2 have finally deteriorated in the last year. - at this age, they could go anytime.


Take your car to a computer specialist (for cars). I work at one and the techs there have fixed so many issues due to computer response isuues. Dealers have to send us cars. Ive seen cars that run rough like a tuning issue, and the techcs will discover its a computer relay issue in the pcm, ecm, etc. If they dont have $60,000 to $80,000 worth of diag/reprogramming equipment, they may not be able to find the issue. Good luck everyone.

2 out of 2 people think this is helpful.

Sorry Paul, i dont know where you bought your Q45, but the Q45t came standard with the NGK BKR5EIX-11 IRIDIUM Plugs - first service at 100k. sorry if someone told you otherwise. 90% of the rough idle, stumbling, poor acceleration problems can be fixed with replacing the plugs, the coils (you can get all 8 on ebay for less than $100), and the MAF (dont clean it, replace it, i got one for $26 delivered on ebay).

1 out of 1 people think this is helpful.

Started at the plugs, then new coils, then new Mass air flow sensor. I have 191k miles on my 1997 Q45 and can't seem to get the rough idle and slight hesitation to stop. The injectors don't seem to be expensive. Should I replace those and then see what happens , or? Any help is appreciated! Robert

Robert you should look into "hot wiring" the coils. There is a way to give them a better positive voltage source. You can splice in additional 12ga wires the coils' wiring harness. Then adding additional grounds to the MAF wiring. Nissans have always been notorious for weak grounds at the MAF and their ignition wiring is not the best... I am going to be adding an additional wire to my coils as well as raising them off of the valve covers in order to relieve some of the heat they get.

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