engine idle very rough

[migurus]

2005 G35 coup with 140K miles, all of the sudden started to idle very rough, as if I lost a cylinder. As soon I start driving and rpm goes above 1000 I no longer feel vibration. Took to dealer, they checked coil, spark, cylinder pressure, could not see any problems. Continued to check on exaust, said there is quite a bit of stuff (from cat. converter) in it, will be checking the converter cores tomorrow. I was told there is a high probability of cat. converter being a culprit. Do you think the tech is on the right path? Does it look like a probable cause?
Thanks.

[RED_DET]

Seems if there was a serious problem the check engine light would be on. MAF, TPS could also cause issues but normally throw codes. Vacuum leak would also cause this issue.

[audtatious]

Thus, do you have a SES light on?

[migurus]

No SES light.
I picked up my car from dealer today, drove a bit and idled and everything is OK. The culprit is debris from catalitic converter plugging exhaust from cylinder. I was explained that at idle the air flows in and out and the debris block air from getting sucked into cylinder, under the normal driving load air just flows out and the blokage does not happen (or this is my interpretation of their explanation)

[audtatious]

Yep, has happened to others. I've luckily never had that problem with any Nissan vehicle.

[XIS]

This also sounds like symptoms of a bad / cracked motor mount...

[migurus]

Status update. After dealer cleaned exhaust my car was happy for some 1000+ miles, now it did hesitate on the cold start two times and Service Engine Soon light came on. Took it back to dealer. Now they say the code indicates mass air flow sensor. Also, mechanic said "oxigen sensors looked like they took some beating" I was quoted $1400 to change MAFS and two Oxigen sensors, parts being very expensive, like MAFS quoted for $600 roughly. I have no $$$ now. I googled this part and most expensive was for some $250, this being not original.

Does anyone know if it will be a problem using non-original MAFS? What would you recommend?

[pae9132]

hey sorry to hear about the issues but I can help a little. I have a used MAF off of my 03 sedan. No issues with it...Just found another one for a decent price and my original housing had some cracks around the bolt holes because I tightened it too much....so I am selling the MAF for $150...It's still in the tube but I would suggest that you place it into your current MAF tube if you do decide to buy it. I use PayPal because they have buyer's protection. Just let me know.

[pae9132]

Another thing. Don't replace your 02 sensors until you do the MAF. These cars are picky and might be throwing the 02sensor code due to the MAF being out.

[Dr. Uzi]

Another thing. Don't replace your 02 sensors until you do the MAF. These cars are picky and might be throwing the 02sensor code due to the MAF being out.

Exactly, with a bad MAF the car is completely confused as to how much air the engine is getting and that will throw everything else out of whack. However, given the mileage of your vehicle if you have never replaced the O2 sensors before now might be the time to do so. Not having much money I would suggest you buy the parts and do the installation yourself. Dealer service= mega bucks and you can save, and learn, alot by doing your own work. Both the MAF and oxygen senors are an easy fix you can do yourself. Look for a how-to on google or something and you may be able to find specific instructions for both installs. Good luck!

[migurus]

thank you everybody, I got the MAF replaced, I'm paying big bucks for having no skills in auto department, so to speak

[pae9132]

did it take away the code for your 02 sensors?

[migurus]

I don't know, I assume they reset and clear all codes after they done the MAF, I don't know how to check O2 sensor codes.