# Rough Idle & A/C issue



## jasonm (Nov 30, 2009)

2008 Sentra 2.0 base model, about 93,000 miles.

Sometimes when I come to a complete stop for an extended period of time (at a red light, for instance), the tachometer will dip sharply and the car will shake roughly. It immediately recovers, and I can hear something clicking back into motion under the hood (probably the A/C compressor).

This does not happen on a consistent basis. When it does happen, it continues once every few seconds until I let off the brake and put the vehicle back into motion.

The most often time I notice it happening is after I have been driving for some time (on the highway, for instance) and I come to a complete stop while my A/C is running and my cell phone is charging on the 12v port. It does NOT happen when the A/C is not running.

Although this problem has been happening for some time, I recently had my car serviced by Nissan (transmission replacement) and completely passed a "complimentary multi-point inspection." I also recently replaced my battery. I'm running full synthetic oil and filter from Firestone, and I'm still on my factory spark plugs. No ODB-II codes.


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## jasonm (Nov 30, 2009)

Dealer replaced the A/C compressor and a hose under warranty due to leaking. However, I am still having intermittent rough idle issues. The A/C compressor kicking on causes the RPMs to drop significantly, and having any sort of electrical load on the vehicle causes rough idle.

I found this video on another forum that demonstrates noise coming from the engine compartment. My car has the same noise.






Any ideas? I'm leaning toward alternator or tensioner, and as I have over 97,000 miles now, my warranty is about to run out.


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## jasonm (Nov 30, 2009)

Now up to 119,000 miles. Recently installed new NGK spark plugs, replaced intake manifold and throttle body gaskets, and performed *correct* throttle body cleaning procedure without destroying the position sensor or electric motor. Also replaced drive belt.

Still intermittently seeing this problem, especially on hot days or after highway driving. I recently had to replace the air duct between the throttle body and air filter for unrelated reasons, so there are no cracks or leaks there.

I did notice a *very* small amount of oil above the third cylinder spark plug (on the coil pack side), so I'll be replacing the valve cover gasket, and since they do have a tendency to warp, I'll also be replacing the entire valve cover (which conveniently comes with a new PCV valve). While everything is torn down, I'll inspect the coil packs again and make sure there are no tears or cracks in the rubber.

I also noticed recently that whoever last serviced my coolant actually put too much water in it, so I will be flushing that out and replacing it with genuine Nissan blue LLC. That's more to protect the CVT than anything, but I did read in the service manual that high engine temperature can cause the compressor to shut off.

My new (as of 1 year ago) air conditioner compressor is holding up well, and recent service did not indicate any leaks or low refrigerant, so it's only the symptom, not the cause. I'm still suspecting the alternator and possibly the tensioner. I'm going to do all of the aforementioned repairs as well as install a new tensioner, and if the problem persists, I'll try a new alternator.

I did find a thread on another forum where someone was having the same issue with their Altima. They performed similar repairs and were finally able to resolve it with a replacement alternator and tensioner. They mentioned first purchasing a remanufactured Ultima brand alternator which did not solve the issue, and then purchasing a used but genuine Nissan alternator which fixed it.

Will report back eventually.


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## jasonm (Nov 30, 2009)

Found another forum thread elsewhere with numerous complaints about the same issue but with the Altima. It's apparently due to the alternator clutch pulley which can be individually purchased and replaced. If your pulley rotates freely in both directions (it should only rotate counter-clockwise), or if there is resistance or dragging when turning it, you need a new clutch.

There is even a TSB out about this issue, NTB10-002, but for some reason it is not listed through nissan-techinfo.com for my vehicle (even though the bulletin itself states that it is applicable to the MR20 B16s). Will inspect my alternator pulley soon and report back.


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