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vg30i idle problem; revs up & down


rmbhs
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My vg30i rev's up and down continuously (approx 1500 rpm to 2000 rpm) until the engine is warmed-up. Other than this idling problem the engine is strong, burns no oil and runs perfectly. It used to do this "revving" only during the winter, but now revs up/down on cooler summer days as well. Once the engine is warm it idles at about 1200 rpm which is higher than the 8-900 specified in the repair manual. Has anyone experienced this same problem ?

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Check your vacuum hoses as well. A leak can cause a high idle.

Plus one on vacuum leak, I run into the same problem with my z24 engine in my d21, same revs 1500-2000 then it drops to 1200-1500 then idles warm at 1000-1200 (I adjusted it to give it a higher idle to more or less hide the leak) a vacuum leak does not affect the motor at all, just makes it confused from what i understand. It looks like your has been adjusted as well as it has a higher than normal idle.

 

There is a tool (no idea what it's called someone should know what it is) but it will find a leak if there is in a matter of minutes, otherwise you have to check your lines which can be very time consuming.

Edited by cvdloc
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In a truck 24 years old, I would recommend replacing all the vacuum lines, just do one at a time, I think in the VG30i engine there is only like 2 different size lines. The rubber gets funny when it gets that old, a small crack towards the end of the lines can go un-noticed. Better to replace them all and be sure, even if the vacuum lines are not causing the problem still should be done.

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If it did this more often on cold days could be the mixture heater below the TB, any codes?

No problem codes; just the 55 code which according to the manual indicates all systems are functioning correctly. I notice that once the system starts running in the "closed loop" mode (ie green light on) the revving up and down stops but it still idles at 1,500. It appears to be revving up and down only in the "open loop" mode.

 

Changing the vacuum lines sounds like good advice. I will do that. Also, I have cleaned the air flow meter and the contacts. New oxygen sensor as well.

 

Thanks for the helpful posts.

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Another thing that will effect the idle and could be keepin it high, just remembered because I had to replace this part on my 87 hardbody, is the wax element, (thermo element I think it is called, I'l look it up, it is I just checked), it is the wax element that the coolant runs through,

 

when the engine is cold the wax is solid and the little plunger is pushed out against the fast idle cam on the Throttle linkage, this causes the idle to be higher when the engine is cold, as the coolant heats up it melts the wax and the plunger moves back in causing the cam to move and close the linkage (lowering the idle to normal idle), when this element goes bad it may be stuck in the high idle position causing your higher than normal idle.

 

 

There is a procedure in the service manual, I have the FSM for the 87 I could scan the page later, that tells how to measure the distance the plunger moves to determine if it is working correctly.

 

This will not trigger a code, if you remove the air cleaner housing it is on the right side of the TB, there will be 2 small (about 3/8" maybe) hoses going to this, one in, one out, check to see if there ai any sign of collant leaks in this area, you can also check the little plunger to see if it moves from when the engine is cold to when it warms up.

Edited by ahardb0dy
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Another thing that will effect the idle and could be keepin it high, just remembered because I had to replace this part on my 87 hardbody, is the wax element, (thermo element I think it is called, I'l look it up, it is I just checked), it is the wax element that the coolant runs through,

 

when the engine is cold the wax is solid and the little plunger is pushed out against the fast idle cam on the Throttle linkage, this causes the idle to be higher when the engine is cold, as the coolant heats up it melts the wax and the plunger moves back in causing the cam to move and close the linkage (lowering the idle to normal idle), when this element goes bad it may be stuck in the high idle position causing your higher than normal idle.

 

 

There is a procedure in the service manual, I have the FSM for the 87 I could scan the page later, that tells how to measure the distance the plunger moves to determine if it is working correctly.

 

This will not trigger a code, if you remove the air cleaner housing it is on the right side of the TB, there will be 2 small (about 3/8" maybe) hoses going to this, one in, one out, check to see if there ai any sign of collant leaks in this area, you can also check the little plunger to see if it moves from when the engine is cold to when it warms up.

Interesting. I'll check this out. Thanks for the info.

Edited by rmbhs
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Was just going to post a "?" mark as I saw you copied what I wrote but did not reply,

 

I have a factory service manual, on my computer for an 89 truck/pathfinder but this morning when I looked through it I did not see the section on how to check the thermo element, I know it's in the FSM I have for my 87 (paper copy), if you want the 89 FSM, PM me your e-mail and I'll send it to you.

Edited by ahardb0dy
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  • 4 weeks later...

You were correct. I have adjusted my thermo element and the revving "up and down" has stopped. Nothing but happiness. After searching for further info I found the following post on another site which describes the problem and fix.

 

"Surging Idle Fixed"

I have 2001 Frontier 2WD with the 2.4L engine. About a year and a half ago, I started having idle issues and went through about everything I could find to correct it. Over the course of several months, I tried new vacuum lines, IACV, PCV, plugs, wires, thermal plunger, and MAF sensor. While the problem got a little better, I eventually took it to the dealer to figure out what exactly was wrong. I was told a thermal switch in the egr system was bad, the intake manifold needed to be removed and cleaned, and even though they knew I had replaced the MAF sensor once, they also suspected that the one I installed might have problems. Anyway, they call me 3 days later and tell me it is ready to go. When I arrive, they had it warmed up and ready to go. The next morning, when its cold, I am surprised to see the engine idle to nearly 2200rpm initially. When I drive it, the idle surges for about the first 3 miles of driving, but then it seemed to settle down and run good. I did notice that even after it warmed up, the idle was about 1000rpm. Doing a search on this forum and several others, that seemed to be a common complaint with many Frontiers. I figured I would give it some time, before calling the dealer that worked on it. I was really hoping I could avoid this, since it such a hassle for my wife when I do not have my truck and I have to use her car. I looked everything over when it was warmed up, looking for anything obvious that could cause a high idle. Then I decided to look at it while it was cold and noticed something interesting, the fast idle cam has two marks where an arm connected to the TPS should be when the engine is hot or cold. I had looked at this when the engine was warm and the "hot" mark was aligned spot on. With a cold engine however, the "cold" mark was about 1/8" from the roller on the TPS arm. Figuring I could always move it back, I adjusted the fast idle cam "cold" mark to be aligned with the roller on the TPS arm. I started it up, the engine idled to 1800rpm, dropped to about 1200rpm and after warming up for several minutes, dropped to about 700rpm. And on top of all that, the surging went away. Of course the fast idle cam "hot" mark is now slightly off, but the truck is now running like new.
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  • 6 years later...

I've replaced my gaskets and made sure everything worked and I still have the revving up and down problem. (Approximately 2,000-2500) Can anyone help me? I have no codes but am pretty sure its a vacuum leak. I just don't know where

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There are a couple of ways to track down a vac leak. One is to spray fuel at the suspected leak location with the engine running. You should hear a change in idle when the engine sucks in air and carb cleaner instead of just air. The other involves a smoke machine. Block off the intake, hook up the smoke machine, then look around for smoke coming out where it shouldn't be. A small flashlight can be helpful for picking up where the smoke's coming from, especially if it's not a massive leak.  Proper smoke machines are great if you can borrow one, but there are lots of walkthroughs on Youtube for making them on the cheap.

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  • 2 weeks later...
  • 8 months later...

Anyone have a good vacuum diagram or a link that shows a good one (easy too follow and understand) for the vg30i, i rebuilt my engine and having tough time remembering routing of vacuum lines

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