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Discussion Starter · #1 · (Edited)
I have an '08 SL hatch with the CVT. Normal idle range for the tach is 600-700 RPMs, but when I'm idling in drive for a few minutes the RPMs will drop to around 400 and the engine will stumble like it's about to die. Immediately afterwards the RPMs jump to around 800-900 for a few seconds and then the needle settles back to the normal range until it happens again. I've had it happen more than once when sitting for an exceptionally long time at a drive thru.

I noticed this problem last fall, but it went away over the winter and just recently returned. It only happens when the car is in drive. If I idle it in park, everything is normal. The AC isn't on, so I don't think it's the compressor. My car's AC compressor sounds like leaf blower at idle, so I'd hear it for sure. It even happens when the blower fan is off. I doubt it's dirty injectors, because I've owned the car since it was new and use Chevron gas. It's maybe had 40 gallons of fuel from other companies total. I also run a bottle of Techron through it every 5K or so.

None of the idiot lights are on, and I just cleaned the MAF sensor and changed the air filter a couple of weeks ago. The engine starts right up on the first crank.

Any idea where the problem might lie? The engine hasn't died on me yet, but I'd hate for it to progress into a serious problem.
 

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I have an '08 SL hatch with the CVT. Normal idle range for the tach is 600-700 RPMs, but when I'm idling in drive for a few minutes the RPMs will drop to around 400 and the engine will stumble like it's about to die. Immediately afterwards the RPMs jump to around 800-900 for a few seconds and then the needle settles back to the normal range until it happens again. I've had it happen more than once when sitting for an exceptionally long time at a drive thru.

I noticed this problem last fall, but it went away over the winter and just recently returned. It only happens when the car is in drive. If I idle it in park, everything is normal. The AC isn't on, so I don't think it's the compressor. My car's AC compressor sounds like leaf blower at idle, so I'd hear it for sure. It even happens when the blower fan is off. I doubt it's dirty injectors, because I've owned the car since it was new and use Chevron gas. It's maybe had 40 gallons of fuel from other companies total. I also run a bottle of Techron through it every 5K or so.

None of the idiot lights are on, and I just cleaned the MAF sensor and changed the air filter a couple of weeks ago. The engine starts right up on the first crank.

Any idea where the problem might lie? The engine hasn't died on me yet, but I'd hate for it to progress into a serious problem.
You seem to have done all the right things, but I did a search and found this answer from another poster with the same year and same problem at stop lights:

"I had a problem once with a car running rough. Ended up being a cracked gas cap. Replaced it and the car ran fine. I guess moisture was getting in or pressure was being released. The cap may have been damaged during a fill-up."
 

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Mine's done that it's whole life. Bought my '08 new in '07, and periodically RPM will tank then bounce back. After 90k miles it's neither improved or gotten any worse.

Likely it's the fuel pump regulator, there's a Nissan Technical Service Bulletin on it. They're faulty in this model range, and the RPM dip is one symptom. Nothing terribly critical, like I said, mine's done it its whole life, and it's never left me stranded.
 

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Check vacuum lines and make sure intake it tight.
 

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Discussion Starter · #5 ·
I know for sure it didn't have this RPM drop until last year. I would definitely have noticed before then.

The dealer replaced the fuel pressure regulator under warranty years ago and it hasn't had any issues with slow starting.

Gas cap doesn't sound too likely either, since the SES light has come on every time I didn't fully tighten down the cap. Freaked me out the first time it happened.

How would I go about checking the vacuum lines and intake?
 

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you can set up a pressure tester by getting an adapter with a pressure gauge and hooking an air compressor up to the intake, then let enough air in until the system is pressurized to about 5 psi. Any leaks will be immediately apparent, by a hissing sound and air escaping. That's my method.

or folks will tell you you can use seafoam or starter fluid, spray it around potential leak areas while the car is running, and if the RPMs jump, you've found your leak. I don't like this, mainly because I don't like spraying explosive gases around my engine bay... just goes against me, but a lot of folks do it and swear by it.

Or there's the trusty but less effective soapy water method. spray suspect areas with soapy water, and if it starts bubbling, there's a leak.

Aside from leak testing you could find someone to log fuel trims, MAF readings, and 02 readings to see what is happening during the RPM event. I have some logging capability, but the occurences aren't consistent enough for me to catch them happening in a log.
 

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Smoke testing is great. Just light up a cigar or cigarette and blow it into the intake tract through a vacuum line. Though I doubt that's the problem. Did you check the EVAP purge valve? Scan tool/data streaming would be useful here, to check all your PCM inputs.
 

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This happened to me a couple times, RPMs would drop for a split second followed by some rough idle like the car was going to die out but it came back up and settled out.

I don't recall how low it went but it was enough to unsettle the idle. I figured it was just a computer glitch and disregard it.

I would be curious if folks with the 4AT or M/T experience this also might be some ghost programing with the CVT equipped models trying to lower the RPMs when it should not when it detects the CVT is in lower speed or stopped and has a delayed reaction.
 

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Guys this is normal this is the ecu testing proper idle. It drops the rpms till it lugs then brings it back up. It only happens when the car is in open loop, Its ok. If it starts dying thats were it becomes a problem. All cars with self learning ecu do this. Hell my 91 mustang did it. Its the computers way of testing for proper tune. The ecu will also run your car rich and lean and very timing on purpose to test sensors and etc. It only more pronounced on at/cvt because of the torque converter as idle on those cars is harder to control than a m/t.
 

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Hello Woogie, good afternoon. It's been a few years but, how did you solve the problem? Could you solve it? I have a Nissan Versa 2009 with the same problem.
Thank you!
 
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