The_Laughing_Man

iTrader: (1)

I recently changed my spark plugs to NGK Iridiums (LFR5AIX-11 #4469) and the car runs perfect. However, at idle there is a noticeable shaking every once and awhile. Not bad enough for me to think that it's a misfire, but I can definitely feel and somewhat hear it from the engine.

I figured it must have been a problem with the gap so I just pulled them out and they're all about stock gap (0.043"). So now I'm out of ideas on why it's shaking at idle.

If you guys have ideas I would really appreciate the help!

AngelsVQ

iTrader: (4)

you sure its all plugged in tightly? maybe you damaged a coil?

The_Laughing_Man

iTrader: (1)

I checked all the connections and they're tight. I figure if a coil was damaged it would be more noticeable. Maybe even a CEL.

installation

You have plug wires 2 and 3 mixed up, drive side, middle and back, switch the two around.

The_Laughing_Man

iTrader: (1)

I wish it was that easy. Both of those wires are in the appropriate spots. I did each plug one by one so I wouldn't make that mistake. Thanks for the idea, though.

Jennifer 2

Maybe it has nothing to do with the plugs, coils etc. Is it possible that in doing this job you inadvertently left a vacuum line or crankcase vent line off, upsetting the F/A ratio at idle? (I’ve never even looked at my engine below the cover/plenum so I don’t know if this is applicable).

The_Laughing_Man

iTrader: (1)

That is definitely something that occurred to me to me today. I'll look into that further, but I cant think of anything that was disconnected besides the tube attached to the intake, which I put back.

JCITY

iTrader: (2)

May sound stupid,but unplug your car...disconnect the hegative pole on the battery for
3-4 hrs or,overnite.Hook it back up.
If you checked everything(vacuum leak would be obvious to me..hose or gasket),this worth a try.
I had a similar problem years ago with another vehicle.Turned out to be a small
fracture of a metal part that made a leak that caused a rough idle.The crack was so small you could not see it.

The_Laughing_Man

iTrader: (1)

I'll definitely try resetting the ECU like that. I checked the lines, but I'll check again when I get a chance.

It actually doesn't shake at all when the A/C is on if that helps at all.

The_Laughing_Man

iTrader: (1)

Well, rest the ECU but it didnt fix anything. I guess I'm going to put the original plugs back in and see if the problem persists. If not, then I'll know its the plugs.

The_Laughing_Man

iTrader: (1)

Things went from bad to worse today.

I was putting in the original plugs when one of the bolts that hold the coil to the valve cover snapped in it. I went to Lowe's and grabbed a bolt remover bit and when I was using it the bit broke off into the bolt and is just about impossible to get out.

To top it all off, even with the original bolts in the shake is still there.

I'm pretty bummed at the moment. Haha

The_Laughing_Man

iTrader: (1)

Well, got my Z back from the shop and they got the bolt out but they have no idea about the shaking.

I'm bumping for more ideas. I'm guessing it's got to be a vacuum issue but I'm not sure where to look. I'm going to spray some carb cleaner around the intake manifold since I installed a plenum spacer a few months ago.

Any ideas on where else I might have a vacuum leak? Or general ideas on my problem?

Really sucks driving your Z knowing something is wrong with it.

The_Laughing_Man

iTrader: (1)

I think I may have found the culprit! I was listening for a leak today and I heard a strong one coming from the PCV valve. I'm sure you're not supposed to be able to hear air from that. I'm going to pick up a replacement tomorrow and see if that fixes my problem.

Maybe I hit it when changing the plugs...? Who knows. I hope this is my answer, though.

obesekat

doubt it..

The_Laughing_Man

iTrader: (1)

Well, I've replaced the PCV valve with a new one and I still have the hiss. The hose on it is in perfect condition and I can't seem to find what needs to be replaced. I've sprayed carb cleaner all around and haven't noticed a difference.

Looking for your help, guys. Is there supposed to be a hiss coming from the passenger side of the valve cover or have I found my problem?

Really appreciate the help.

Bret86944

iTrader: (4)

If the car runs fine except at idle, how do you even know there is a problem? Is the shake really that bad? Could be warmer weather, different fuel mixture this time of year, who knows. Are you getting bad gas mileage or something?

The_Laughing_Man

iTrader: (1)

The shake isn't erratic, but enough to know its not right. I've tried different gas since it started and it's been doing it on cold and hot days. My gas mileage is fine but it's just knowing that something isn't right with my car that has me trying to fix it. It's annoying to stop at a stop light and feel that shake.

I'm optimistic now that I've found the possibly culprit, that loud hiss from the passenger valve cover. I just can't pinpoint it now. I'm hoping someone might have had this problem before or has any suggestions.

Thanks for the reply.

The_Laughing_Man

iTrader: (1)

Well, I've taken it to a shop three times with no luck. They said it would have to get worse before they could figure anything out.

I really have no idea what I could have done during a spark plug change that a reputable shop couldn't fix, but I guess I'll just have to live with it for awhile.

Thanks for the help and if anyone else has any ideas at all please let me know. I would like my Z to be perfect again.

installation

The only other thing I can think of.

On my first 350z I damaged the throttle body by cleaning it. I would get an eratic stutter once in a while. Did you try to clean it or maybe dropped something on it while the car was off?

The other thing that someone said was a vacuum leak which is the only possible scenario. Maybe your plenum bolts back off? Loosen them alll then re-torque in order.

If that still fails....

The_Laughing_Man

iTrader: (1)

Thanks a lot, I'll inspect the throttle body. I hadnt thought about that. As far as vacuum thats exactly what it seems like it would be. All the symptoms point to that but I cant find a leak and neither can the shop I take my cars to. I've checked the plenum bolts and they're tight, but I'll try re-torquing them.

That pic probably explains it.

EDIT: Did you end up having to replace your whole throttle body?