Has anyone else experienced this? Got an 08 SE V6 4x4 (not AWD). It has 62k miles and just had the 60k service done.
Everything starts fine and the RPMs stay steady at idle. After about 30-40 seconds it starts to vibrate a little more than normal and it lasts about 4-5 seconds. This repeats. No vibrations during driving at all.
Thanks for the help!
vibration at idle every 30 seconds or so
Moderator: volvite
I am 95% sure it's your A/C compressor turning on and off. This is normal. If you're really worried about it, open the hood and see whether the plate on the front of the compressor spins when you hear the engine "lugging." It's on the left side of the engine and driven by the fan belt. You're looking at the end cap over the magnetic clutch that engages to drive the compressor when the ECM says it needs to provide pressure.
Alternatively, you can switch off the A/C and see if the sound goes away.
I just got a new compressor today, so I can verify that both a dying compressor and a brand new compressor will make the engine behave the same way at idle
Mine lugs a little more under the compressor load when it's warmed up.
(Incidentally, a dying compressor sounds like a vacuum cleaner whine and it may be louder than your engine when its running...)
Alternatively, you can switch off the A/C and see if the sound goes away.
I just got a new compressor today, so I can verify that both a dying compressor and a brand new compressor will make the engine behave the same way at idle
Mine lugs a little more under the compressor load when it's warmed up.(Incidentally, a dying compressor sounds like a vacuum cleaner whine and it may be louder than your engine when its running...)
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ElegantSpoon
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silver x0ne
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Same here.... I thought it was the cooling fan/radiator fan coming on too... the second I come off the highway and sit at a light for all of 10 seconds, it's n... always thought maybe a wacky bearing or something, it seems to be increasing in frequency as well as severity (ooo look at me using big words.. )
I tow a lot, so it's never bugged me in the past... why start now?
Mr Mayor
)I tow a lot, so it's never bugged me in the past... why start now?
Mr Mayor
Mine does the same thing (I have an 02, so It's not the same i know). My uncle is a GM certified mechanic and works at a GM dealership. So I ask him lots of questions. I wasn't able to get him to listen to it being that I didn't drive my pathfinder that day, but based on what i described to him, he said that it was probably just the engine trying to find the correct idle speed. Much older cars used to have a screw that you would have to twist to get the idle speed, now it's all computers. I will have them check it out however when I have the 60k service work done...just to be safe
The idle isn't varying...watch with a code scanner, it's very stable. The load and other transients however do. Fans, compressors, other loads coming on and off, temperature, etc. will oscillate and affect the engine one way or another. This means more or less fuel and air and bigger or smaller combustion events, which feel different in the truck.
Engines vibrate, and big engines vibrate a lot. I'm not sure why this is a big deal suddenly. You have the dynamics of the rotating shaft and its imbalances (harmonic behavior), plus the resultant imbalanced forces from combustion on the pistons and the momentum of the pistons orthogonally projected from the shaft centerline.
That's lots of things out of balance, even in something with so-called "perfect" natural balance like a 90 degree twin or inline six.
The real underlying answer for what you're feeling is that with some kind of load or other change the engine is varying fuel and air intake to maintain idle RPM. The bigger or smaller bangs don't result in a momentum or RPM change under a heavier load, so the engine will necessarily feel different. It's most noticeable when the compressor switches on and off, but that's why you feel that lugging.
You should be able to see this with your code scanner (I can with mine.) Watch the throttle setting and RPM indicators if you can. The throttle doesn't move much but it does move, while RPM stays pretty steady.
Anyway...the truck's not broken.
Engines vibrate, and big engines vibrate a lot. I'm not sure why this is a big deal suddenly. You have the dynamics of the rotating shaft and its imbalances (harmonic behavior), plus the resultant imbalanced forces from combustion on the pistons and the momentum of the pistons orthogonally projected from the shaft centerline.
That's lots of things out of balance, even in something with so-called "perfect" natural balance like a 90 degree twin or inline six.
The real underlying answer for what you're feeling is that with some kind of load or other change the engine is varying fuel and air intake to maintain idle RPM. The bigger or smaller bangs don't result in a momentum or RPM change under a heavier load, so the engine will necessarily feel different. It's most noticeable when the compressor switches on and off, but that's why you feel that lugging.
You should be able to see this with your code scanner (I can with mine.) Watch the throttle setting and RPM indicators if you can. The throttle doesn't move much but it does move, while RPM stays pretty steady.
Anyway...the truck's not broken.
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