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Rough Idle

I have a 97 Nissan Altima automatic with 180,000 miles. The check engine light has been coming on and off for about 6 months, but every time I take it in, they say there’s nothing wrong and that the car’s just old. I don’t have many problems with the car in general. The spark plugs and battery were replaced a year ago, and I just got the oil and air filter changed 2 weeks ago. Today, I noticed that the car is idling rough at lights. It does no help if I put the car in neutral. If I coast in drive or reverse, the buck is very strong, but as soon as I hit the gas, it starts to smooth out. When it is idling, the RPMs fluctuate between 500 and 1000. Any suggestions? It’s a little concerning that it runs so rough at stops, and I’m not trying to break down!!

You may have a dirty IAC (Idle Air Control) valve and/or a dirty throttle body.

The surging (RPM fluctuation) could be related to a a faulty vehicle speed sensor.

Also look for vacuum leaks. And any shop you’ve gone to w/ a check engine light that says “nothing is wrong” is one that you shouldn’t go to anymore.

You need to find out what codes are being triggered. Many auto parts stores will read your DTCs for free (Autozone is now doing a big ad campaign on this). Go get them read, write down the exact code (something like P0123) and post them.

Could be a lot of things. An EGR valve that is sticking open sometimes would probably do about what you describe. As would a cylinder that is misfiring (maybe), or any of the things other posters have mentioned. Did they tell you what scan code was associated with the Check Engine light?

Got the diagnostics back. There was a vacuum hose that had come loose in the car, which unfortunately has not fixed the problem. The O2 sensor and NOX sensor are messed up. Looks like about $1200 in repairs on a car worth about $600. How much will these things actually affect my driving, besides hampering my already cruddy gas mileage?

Got the diagnostics back. There was a vacuum hose that had come loose in the car, which unfortunately has not fixed the problem. The O2 sensor and NOX sensor are messed up. Looks like about $1200 in repairs on a car worth about $600. How much will these things actually affect my driving, besides hampering my already cruddy gas mileage?

Please provide a list of specific items that will presumably all add up to $1200 - that sounds a little nutty. Is this a dealer that you are talking to?

OK…I was off on the names. EGR valve-$229.12+ $85 labor. Knock sensor $235.98+ $484.5 labor. $15.90 for an upper intake gasket, and $59.90 + $40 labor for fuel injection cleaning.