Less than smooth idle...

[Wacko]

My 2001 4.0L with 57K miles starts and runs strong. However, I notice that at idle it feels like an engine miss maybe every second or so. I don't know if it is consistent 1 second intervals or if it varies. No check engine light. No electrical problems. Voltage, temp and oil pressure are all good. I do need to check if it happens in park or drive only. Although dad lets me I drive slow in the driveway. Sorry, Rainman reference.

Is this normal effect in a transverse V8? I just got the car and was wondering if others experience this or is it a sign of some future problem?

Thanks,
Paul

[auroralover]

Wacko,
my 97 with the 4.0 is as smooth as silk at idle and all through the rpm's, with 98000 on the clock. No, I don't think you should have any type of miss, but I could be wrong.

[TJM]

I have heard the Northstar compared to the old Packard straight 8 that you could balance a silver dollar on the head while it idled.

Start with a good fuel system cleaner.

[Wacko]

Thanks, folks. It is very subtle, but I noticed it right away. Who knows what the prior owner(s) used for gasoline. I just used my first tank of premium.

I'm used to my 325, an in-line six, with no vibrations or perturbations. <-- big word alert; I wonder what it means.

TJM, can you recommend a fuel system cleaner? STP?

[mission008]

get NOS! just kidding, STP is a good brand, I've used that before and it worked pretty good. If the fuel system cleaner doesnt do the trick then I would look into checking your timing...that could certainly throw off the idle slighty.

[TJM]

wacko said:

Thanks, folks. It is very subtle, but I noticed it right away. Who knows what the prior owner(s) used for gasoline. I just used my first tank of premium.

I'm used to my 325, an in-line six, with no vibrations or perturbations. <-- big word alert; I wonder what it means.

TJM, can you recommend a fuel system cleaner? STP?

HEY, that's a $10 word! $5 words are OK but nothing over $7.50 is allowed in this forum. Ya made me dig out my thesaurus just to narrow down the root. I had to read it 3 times just make sure it wasn't sexually explicit. JEESH...

Yup, any brand name should do - its likely just some moisture in the tank or maybe a new fuel filter is in order.

[BNICOV]

Run a tank of the highest octane fuel you can find in your area with 2 bottles of injector cleaner. That way the added detergents in the fuel and the injector cleaner should be able to loosen up any deposits. Take your car to a quiet highway and let'er rip. A couple of trips to the redline would be very helpful in cleaning deposits on the valves as well. Your car can't have the timing adjusted as it is controlled by the computer. Hopefully this should take care of the problem. If not, you may want to change the plugs, fuel and air filters.

[mission008]

do we have timing chains or belts?

[TJM]

Chains - 3 actually:

clubs.hemmings.com/clubsites/allantelonestar/image_gallery/scans/norstareng.jpg

[Aurora40]

That's not normal, except when doing a cold-start. For about 30 seconds it runs at a high idle and runs kind of crappy. I believe it is to warm the cats up.

I'd suggest Chevron's Techron if you want a fuel system cleaner.

[Wacko]

The fuel system cleaner will clean the injectors basically. But what's the possibility of the throttle body being gummed up like the classics? Could this be the cause of the idle issue?

[Letitroll98]

STP, Lucas, Marvel Mystery Oil, etc are all junk. Use Chevron Techron as a fuel system cleaner as noted by A40. But even the well designed Techron product will do very little to clean dirty injectors. Get the professional cleaning that goes through the vacuum line if you need injector cleaning. However I doubt if that is the problem. This is most likely a spark plug wire (1st), a spark plug (2nd), or a coil pack (not likely).

As an aside, the best fuel system cleaner is maintenance. The best maintenance product is Fuel Power 60 available online at www.lubecontrol.com/index.htm You put 1 oz per gallon in a every fill up and it will keep your entire fuel system clean and lubricated. There are claims of increased mileage that I haven't noticed.

[Wacko]

Service manual on the '01 says to inspect the throttle body for deposits every 30k miles, I believe. So with 57K on it now, I think I will check it. I'm sure the previous owner(s) would not have had it checked.

I bet this might have something to do with the very slight stumble at idle. Unless there's a vacuum leak with the nitrous oxide system.

[bld]

I have had excellent success with the BG brand of intake & injector cleaners.

A miss will not be caused by a dirty throttle body, though. Stumbling, rough idle, yes. Miss, no.

Letitroll pretty much nailed the most likely causes of a miss.

My '99 would probably pass the silver dollar test, even with >90, 000 miles on it. Smoothest running engine I've ever had.

[Wacko]

Letitroll suggested a plug wire, among other things. I have a 2nd gen; no wires correct?

By the way, I'm not convinced it is a misfire (there is no check engine light). I was not sure how to describe the problem, hence the title of the thread. Also, once off idle it is (apparently) smooth as can be.

[Custom88]

engine mounts maybe? I know that I can feel my V6 idling all the time and when I get it above idle the vibration goes away. it's not really a vibration but you can "feel" the engine running. On cars of the past you could not feel them run at all. Our 00 Bonnies with the same chassis feel exactly the same as my car at idle. You can slightly feel the engine idle. The earlier G chassis (like the classic aurora) I never felt it. I think it's the motor mount design. You said the engine feels and sounds healthy otherwise, no? If it is I'd guess it's just normal vibration from the engine idling.

[Wacko]

The geometry and firing order of V-6 engines (and other designs) lend itself to running not as smooth as a V-8, V-12 or in-line 6. However, modern V-6's usually try to counteract this tendency with balance shafts inside the engine with mixed results. It's been a while since I've owned a V-8; so perhaps it is normal. One other thing, it is not at a predictable rate. It seems random. I need to sit in another Aurora to compare.

Good advice about the engine mounts. I'm not sure how to go about diagnosing that though.

[Custom88]

wacko said:

The geometry and firing order of V-6 engines (and other designs) lend itself to running not as smooth as a V-8, V-12 or in-line 6. However, modern V-6's usually try to counteract this tendency with balance shafts inside the engine with mixed results. It's been a while since I've owned a V-8; so perhaps it is normal. One other thing, it is not at a predictable rate. It seems random. I need to sit in another Aurora to compare.

Good advice about the engine mounts. I'm not sure how to go about diagnosing that though.

your best bet is to sit in another V8 Aurora, yes. I understand that the V8 is always smoother than the V6. I was just saying that I've felt the same engine in two different cars and in one car you cannot feel the engine run at all, but once it was placed into the G chassis (which our Auroras use) I could then feel the engine running all the time.

[Wacko]

Pardon if I came across as a know-it-all 'cause I definitely don't know it all. You know, I don't even see the tach needle move but I feel it in the seat of my pants at a stop. I'll keep my eye on it. If it gets worse, then maybe it'll generate a DTC.

[Custom88]

wacko said:

Pardon if I came across as a know-it-all 'cause I definitely don't know it all. You know, I don't even see the tach needle move but I feel it in the seat of my pants at a stop. I'll keep my eye on it. If it gets worse, then maybe it'll generate a DTC.

oh no, not at all. I didn't mean to come off the wrong way either. I just figure that sometimes I post unclear and was just clearing up what I really meant. .

One other reason I believe it to be motor mounts is because on many other vehicles when you go from park or drive, you hardly feel it. On our cars you get a thud when the gear engages. I'm not sure the cause exactly though?

[Wacko]

I still have this annoyance. And that all it is at this point. I am not sure how to check the motor mounts but good point, Dan.

In changing the PCV three days ago I noticed that the rubber seat does not make a snug fit with the valve. I wonder if this is a source of the slight stumble. Hmmm. I do have a vacuum guage that I should hook up to the car and see if the needle bounces around.

[bksss]

I remember seeing a service advisory about 1.5 years ago concerning camshaft replacement on the 2nd generation 4 liter Aurora. I had access to service information when I worked at a previous job. If and it is a big “IF” my memory serves correctly, the camshaft problem could cause rough idle. It was not something that GM covered on warranty but I think some poorly manufactured camshafts were causing minor problems. Anyone have any current information on this. My Aurora has a less than perfect idle. I have not paid much attention to it but would like to know what is causing it.
Kim

[Wacko]

Good to know. This was specific to the Aurora 4.0 or all Northstars in general?

[bksss]

I did a search on Aurora and the camshaft problem came up, I do not know if it included other Northstars.
Kim

[Wacko]

Kim,

It would appear this is what you found, correct?

www.caddyinfo.com/howtoroughidle.htm

A quote from the author regarding the original camshaft vs. a redesigned one to deal with owner complaints of slight stumble at idle.

"Neither cam is "better" as one idles a little better and the other has a few more HP. Can't have your cake and eat it too. I'd rather have the power."

I tend to agree.