Questions and Answers

Nissan Pathfinder Fluctuating Idle Q. Hi Vince, I have a 1996 Nissan Pathfinder with a 3.3 liter V-6 and manual transmission. The problem is at around 3,000 rpm the engine will lose power and then surge back up again in rapid succession. It will lose 500 to 1,000 rpm at a time and then comes back so it sort of fits and stutters.

It happens in any gear at this rpm level but is perfectly smooth before 3,000 rpm and beyond 3,500 rpm. When this first happened, about six months ago, we took to several mechanics who all had different opinions.

We've fixed the exhaust manifold, completely cleaned out the fuels system, replaced bad sensors, etc. Spark plugs and wires are new. Finally, a good cleaning of the throttle body made the problem disappear. But now it is happening again and cleaning the throttle body does no good.

I've checked other parts of the air intake system, like the PCV and EGR valves, but I don't think they are the problem. I'm beginning to think it is some kind of block in the exhaust system. I took it to one exhaust shop, though, and they wouldn't even look at it because the problem I described didn't sound like an exhaust problem to them. What do you think?

Thank you very much!
Daniel

A. Well Daniel, you know what they say about opinions.

It has been my experience with Nissans that this problem is usually caused by a dirty or bad Idle Air Control Valve (IACV). I would try removing the IACV and cleaning it thoroughly, as well as the air passages in the intake manifold.

You can check the valve itself. Check the resistance between the two terminals with an ohmmeter. The resistance should be approximately 10 ohms at 77°F. Also make sure the plunger moves in and out without sticking or binding and the spring is not broken.

Another common cause is a loose or worn timing belt. You didn't mention milage, but the timing belt should be replaced every 60,000 miles. This is more important in vehicles with a manual transmission.