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post #1 of 11 Old 08-14-2017, 01:58 AM Thread Starter
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Engine surge

I just installed an overhauled head on a 2007 Nissan Versa 1.8 due to burnt exhaust valves. When I started it up it runs great but the engine surges from idle to 2000rpm then back to idle every 15 seconds. I found an electrical connector disconnected down close to the pre cat O2 sensor but I cannot find what it connects to. I'm not sure if this connector is supposed to be connected to something or if this connector is causing the problem
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post #2 of 11 Old 08-15-2017, 01:31 AM Thread Starter
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Idle relearn???

So I went to a Missan Dealer service and told them the same thing. (See my first post). They seemed to know exactly what the problem was. They said the car needs an idle re-learn and they would be happy to do it for $120. Does anyone know what an idle re-learn is? Can I do it myself? Thanks
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post #3 of 11 Old 08-15-2017, 02:25 AM
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Quote:
Originally Posted by mmeeuwse View Post
So I went to a Missan Dealer service and told them the same thing. (See my first post). They seemed to know exactly what the problem was. They said the car needs an idle re-learn and they would be happy to do it for $120. Does anyone know what an idle re-learn is? Can I do it myself? Thanks
A quick search for "idle relearn" revealed this: How to perform a Nissan Idle relearn and a whole bunch of similar sites.
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post #4 of 11 Old 08-15-2017, 04:05 AM
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Not 100% sure on these as to extras needed but commonly an idle relearn is simply wiping the computer of all codes and then starting engine up to let it idle for the prescribed amount usually around 15 minutes or so. You lose KAM with killing power like disconnecting battery for an hour, and then the learned idle in memory is gone to have to learn it again. Car may run like crap at first but keep at it, the longer it runs the better the idle gets and will be learning the last ultra-fine tuning of it as you drive for the next 3-4 hours.

Short version is, longer you drive car the more info the ECM gets to fine tune all of it including idle. That happens on every ECM controlled car on the planet.

FYI, if not done yet I would be looking into what burned those valves......................may happen again.

Last edited by amc49; 08-15-2017 at 04:08 AM.
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post #5 of 11 Old 08-15-2017, 05:12 AM Thread Starter
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Thanks Slick and AMC for the replies. I will look up Nissan idle relearn. Thanks. I just bought the car from a younger kid. May have been driven hard. I put on an overhauled head so the clearances should be ok. I drive my cars easy. The goal is fuel savings so I will keep an eye on it. Thanks
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post #6 of 11 Old 08-15-2017, 05:47 PM
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Driving them hard has very little to do with burning valves, almost always a cause for it if more than one.

This............

' I put on an overhauled head so the clearances should be ok.'

Famous last words. Being the original issue was burned valves you should want to guarantee that yourself since not being right one way (tight) WILL burn them again in short order. Another is clogged cat or if a ceramic brick type breaking up in pieces to then migrate into exhaust and/or muffler to stack up and block flow, again, burned valves.

Hope you used new head bolts as the originals are likely TTY ones and one time use only....................nice way to blow a head gasket too early.

Last edited by amc49; 08-15-2017 at 05:55 PM.
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post #7 of 11 Old 08-15-2017, 09:37 PM
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Not enough backpressure or too free flowing exhaust causes burnt valves too.
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post #8 of 11 Old 08-16-2017, 05:09 AM
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Nope, old wives tale. Why do open headers work better? They can actually produce a hard vacuum and the opposite of back pressure. In fact, if not making a vacuum they are junk and not working. How they scavenge.

It's actually only when the pipe gets short enough to be able to back suck cold air in that the valves burn, the differing temps warp the white hot valve then it burns. Super short pipe or broken close to the front. Where the misapplied too low back pressure idea comes from.

The old radial aircraft engine guys knew that too short exhaust stubs burned valves back in the early 20th century. When pipe is too short the vacuum reverse pulse following the positive sucks back in a big chunk of cold air when it hits atmosphere and then the following reversion spike sends it back to the valve.
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post #9 of 11 Old 08-17-2017, 01:04 AM
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To idle relearn on a honda you find your radio codes first and write down radio presets and anything you do not want to loose.

Disconnect battery and wait 15 minutes. Connect battery start and let car idle in a safe area with brakes on in park, parking brake set with all accessories off for 15 minutes. Then drive the car as usual.

Hondas with automatics also learn to shift to the way they are driving so a car thats been shuttles back and forth from the car wash on a lot can drive funny at first then as you drive it daily it seems to change and get better in regards to performance and mpg.

If you change anything on the car like add a cai, cat back, etc its a good idea to do this to let the computer reset.
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post #10 of 11 Old 08-17-2017, 08:14 AM
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X2, often a fixed problem where a mechanical part was changed for new does nothing as the computer is still using the changed up software it modded for the broken part; you must wipe that software with a battery disconnect to force a new relearn to make the car then re-adjust to run correctly. The computers are often still not quite good enough to recognize a brand new part and it could even be an OEM issue where they want you to think you have messed up the car to have to bring it in to the dealer to fix. That is a LOT more common than you think, the entire industry is running that way as fast as they can.
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