O.K. this may be a long one, but I want to be specific with details...

My skyline has an idle problem. It started about a month ago. It use to idle perfectly around 650 but lately has been sagging to around 500 with moments of roughness with it. It never dies out, but starts to shake a little when it goes down to 500 RPMs.

I took it to nissan and they put it on the computer and it did not have any error codes, so they said nothings wrong. They had it a week. I went to pick it up and it was doing the same things, so I had the nissan guy ride with me. when we stopped at a light, and the RPM's dropped to 500, he said that the car was really lean when it did the drop to 500, but not lean enough to registar an error code.

Not really know what can cause this. I have read on here MAF, throttle body, O2 sensor...etc...but has anyone got an idea to narrow this down?

The only thing I have done to it is put in an air filter (not OEM, but Fram) and added some octane boost to a couple tanks of gas. These are the only things I have done different in the last couple of months with the car. Could either of these items cause this idle problem??

Nissan told me that the only way they will know what the problem is, is when the car actually registars an error code. If not, they said I have to deal with it.

any info or help would be much appreiciated.

 

That's the rub OBD2 allows +-20% deviation from normal calculated values to minimize MIL light activation.

Octane Boost does it contain MMT or other organometallics, those can coat the plugs, O2 sensors, Cats causing inaccuracies.

Try a can of BG44k fuel injection cleaner in 10 gallons of fuel...........any changes after this treatment? How many miles on vehicle?

 

I will give it a try. I live in Japan, so could you tell me what BG44k FI cleaner is or would any fuel injection cleaner work?
It has 57,000 kilometers (around 35,000 miles)

 

Techron will work at a higher concentration say 4 x 11 ounces in 10 gallons.
Important to get a high level of detergents to clean things fast so you notice any change. Many common aftermarkets are near worthless due to weak amount of detergents in carrier liquid---the bulk of 11 ounces.

Returnless fuel systems are harder to clean.

CRC makes a professional spray MAF cleaner use very carefully from a distance of 12 inches...........low force on elements or you will damage them requiring replacement [$400].

Read your FSM carefully about the dangers of cleaning throttle bodies with electronic controls................alway disconnect the battery to shut down self control and dangers of getting out of calibration!!!!!!!!!!!

 

Thank you, Sir.

No change after the FI cleaner. does the same thing. Too bad it couldnt have been that easy. : )

I dont think I will attempt the throttle body or MAF sensor cleaning. I have to admit that Im not too mechanically inclined, so I wouldnt want to screw anything up.

Since this problem, I feel, started after using the Octane boost, would the throttle body or MAF be the problem anyway? From your earlier mail, it seems that the O2 sensor, plugs, or cat would be the problem being coated as you described.

dont know if this helps in the diagnosis of the problem, but it seems to be fine with the a/c on. just a little fluctuation in the RPMs after being on the throttle then letting up. It drops down to about 800, at any speed, then immediatly goes back up to where it should be depending on speed and how fast Im slowing down.

 

How long has it been since you last used the octane booster. Has it been long enough to where it has actually been all used up? If not, I would suggest taking a long ride and burning it all up, and stop using it for a couple of tanks.

 

Check your vacumm lines for leaks. I had the same problem on my Jetta and it would idle down until it almost stalled out (in neutral) I just had a bad hose.

 

Thanks you, Gentlemen.

I havent used the octane boost in a couple of months now. It seems the problem is getting worse and worse.

I also checked the vacuum as much as I can tell, there doesnt seem to be a leak. Dont hear any hissing anywhere.

Just frustrating to me to have Nissan tell me to "live with it" until an error code is shown. I pretty much told them to change whatever or fix anything they need to fix. Not really concerned about cost if its within reason. They just seem not to want to work at finding the problem.

Thank you guys for all the imput. Cant say enough good things about this site and the people on it. Very knowledgeable and helpful.

 

Guys,
Just an update if someone else was having this problem..... After 2 weeks at Nissan, they finally found out what was causing the idle problem.

coil packs and plugs were "bad". Not even sure what they meant by "bad" but, that was the problem. Working like new now. No rough idle or shimmering of the car. Cost me $900 plus tax and labor, but well worth it for me to finally know and fix what was wrong.

Nissan also threw in a ECU flash that they said was updated. Not sure if that was on the level or not or they just reset the ECU.....all I know is that its fine now.

 

Hey thanks for the info......my G has been acting very similiar to your car.....and the dealership does not want to do anything since it has not thrown any error codes.... I will bring that up to them the next time I take my car in.....

 

Good to know. Not often we see bad coil packs without ECU mods.

 

shouldn't this be a warranty repair? For an expensive car, I'm surprised they had u pay for bad coil packs. Plus if its just coil packs and spark plugs, how did it add up to $900?

 

6 coil packs and plugs with labor could easily be that much $. The plugs alone are a good $80-100 at the dealer.

 

my previous car factory coil pack was $30. ngk iradium plugs are around $10 each. Thats a lot of extra $$ for good will. Anyway, maybe the piece of mind was worth $900 to him.

 

well glad to know that is your problem