this is another one of those "is this normal" type questions.

okay, so i have this vibration (steady, no fluctuation) at idle that is nagging the hell out of me. my car doesn't die or antyhing it's just annoying.

so anywho i've narrowed it down to two things either 1)charging system or 2) new exhaust time.

this has to do with the charging system thing.
let's say i'm at idle in "D" at night with my headlights on. my idle is at about 600rpm. i roll down my window and roll it back up again. when the window rolls fully back up my interior dashlights go from regular regular intensity to slightly less regular intensity and my rpm drops by about 50rpm (to about 550) and my vibration (which is omnipresent at idle in "d") gets a bit worse. then it goes right back to "normal" again.

now, i don't have any fluctuation in brightness of interior lights (or exterior) for that matter in regards to accelleration...just at idle in drive...accompanied by the aforementioned vibration. i have never had the battery indicator or CEL light come on (yes they do work though).

so tell me folks...does your max do the same thing? i'm just really stumped because i'd assume if this were my alternator i'd have more issues when accellerating.

if you have any ideas, that would be great..i can't really look at my car indepth until my next day off (tues).

thank you!
*jared

 

Jared,
I have the same MAX also at 130K miles. This sounds normal for this car. After mine warms up, it does almost the same thing.

I do not agree that it could be the charging sys or exhaust.
Suonds like the idle is just a little to low. The FSM says the idle should be at 700 RPM. Sure, the alternator will pull the RPM down a little, this is normal at idle.

Lets check the charging sys anyway....
Clean battery posts...right?
Charge the battery.
Using a digital voltmeter........
Engine off.....Turn the head lights on for 15-20 min and observe battery voltage. Should not fall below 10.8 volts. If it does fall or will not start the car after only 20 min, the battery is toast.
Start the car..... Voltage should go to 13.8 to 14.2 after short time.
OK so far......

Idle speed....
First thing I would do is clean the TB {throttle body}.
They get a gunked up and dont allow proper air to pass at closed {idle} position. Spray it with carb and choke cleaner and scrub it with a tooth brush.
The idle on these cars is adjusted via the {IAC}
IDLE AIR CONTROL VALVE.
Dont mess with this unless you know where it is and what to do with it! Simple check to tell if it is working......Does the car start when cold at high idle of about 1500 RPM, then slowly fall to normal idle? If yes the IAC and coolent temp sensor are working OK.
The IAC has an adjustment screw on the top of it to set idle speed.
CounterClockWise is +, Clockwise is -.

Exaust time? Are ther any holes in it? Are all the hanger brackets there? Mine had that hanger bracket at the CAT totally rusted away, was only hanging from the engine and muffler!!! Not Good!!!

I have read threads about his that suggest it could be engine mounts.
Serach if you wish to explore that direction......

Thats my thoughts on your ?
Jim

 

wow, very concise reply..thank you.

so you've got the vibration thing too, annoying, isn't it?

startup is exactly how you described, revs about 1400rpm and then falls slowly down to normal idle...idles cold about 800...nice and smooth, but after it's been driven awhile and warmed up the idle is about 600 usually...slightly more without headlights, etc.

i've been meaning to do the tb cleaning (there's a really nice site with pictures and the whole 9 yards on it), but just have been neglecting it. ignition system is nice and new, fuel filter about a month old.

exhaust wise, i can hear a leak of some sort somewhere...i assumed it was from the rusty-looking flanges.

i haven't touched the iac (other posts said not to compensate for crappy charging with a higher idle setting), though i did adjust the idle speed on my gf's altima and it really smoothed out things for her.

thanks again! anyone else?
*jared

 

Both of the automatic maximas in my family exhibit these same symptoms (92SE 135K, 95GXE 165K). Both of the manuals do as well, although the vibration to a lesser extent (93SE 117K, 99SE 58K). All run great, so I wouldn't stress over it.

Definitely do the TB cleaning... you'll wish you had done it sooner.