Uneven rough idle

Ok, I believe you all previously told me you thought it was the SC coupling. I shot a video the other day of it idling and revving lightly so you could hear it better. What is it?

Also, why does my car idle like it has a cam sometimes at the beginning before I give it some gas? It's very strange and it goes away as soon as I rev it a little and it comes back down. Also something I noticed in hindsight, why didn't my light under the hood come on?

Sorry, video was cut a bit short because my camera has a small memory card (Only like 32 or 64 MB I think).
http://media.putfile.com/Idling-vid-18

well that sounds like the valve train but im not sure. but if its from the coupling i dont know

is the car cold? It sounds like it is and thats the intake. It always sounds like "rocks" on a cold startup.

you're light under the hood only comes on when you turn on the headlights.

dreww wrote:

is the car cold? It sounds like it is and thats the intake. It always sounds like "rocks" on a cold startup.

you're light under the hood only comes on when you turn on the headlights.

Well, it still does it when it's warm but it's not as loud. I'll have to film it when it warms up, that was a cold start.

Shintsu wrote:

dreww wrote:

is the car cold? It sounds like it is and thats the intake. It always sounds like "rocks" on a cold startup.

you're light under the hood only comes on when you turn on the headlights.

Well, it still does it when it's warm but it's not as loud. I'll have to film it when it warms up, that was a cold start.

yea, I hear it warm too, just alot louder cold.

Vacuum leaks can cause your car to idle poorly when cold.

take a long screw driver and use it like a stethoscope on the s/c snout/housing. see if that is the source of the noise.

you still have the original coupler after 143k miles right?

Mr.Riviera wrote:

take a long screw driver and use it like a stethoscope on the s/c snout/housing. see if that is the source of the noise.

you still have the original coupler after 143k miles right?

While the car is on? Uhm that doesn't sound like the wisest idea on something that's spinning very fast.

I don't think we've replaced it so unless the original owner did, no it hasn't. (We're the second owners).

Haha.. I've called him out on that screwdriver thing before! Exactly how far is the screwdriver launched when it catches the fan blade of the alternator?

yes with it on! you dont hold it near the alt blades, or the belts.
i hold it so it rest against the snout by the wire loom. i'm telling you it works. i use it to listen to the bearings in the pulleys too, but you have to be much more careful doing that b/c if it does happen to slip...

if you want, go out and buy a stethoscope and use that instead.

AA wrote:

Haha.. I've called him out on that screwdriver thing before! Exactly how far is the screwdriver launched when it catches the fan blade of the alternator?

i must be a slow learner then

i've never had a problem with it slipping around, but the screw driver i'm talking about is more likely to be used as a breaker bar than to screw something.
i know someone on here, besides me, has used this shade tree mechanic trick before.

I use a piece of rubber vacuum hose.

My SC 97 Riviera has 191,000 and has a new supercharger on it (previous owner was a lawyer). When you are at a stop light the car idles to about 700 but its a rough idle. Car had a complete inspection but I am wondering what would cause this in my Rivy? Is it just the way supercharged 3.8's are?

Thanks
Josh

Oh, heck no.

first - a 'complete inspection' does not usually mean that all components were inspected and refurbished to new condition, does it?

here are some things to check for that rough idle.

1) you have new blower but when was it put on and what kind of gas do you burn? what did the lawyer burn? point is that rough idle is often result of bad feedback and sometimes can be easily fixed by thoroughly cleaning the throttle body, or replacing the TB with a new one. and 'thorough cleaning' does NOT mean pulling the air horn and spraying. It means removing the TB and using a pretty aggressive solvent to clean it. This is more important if the Riv is/was burning regular gas instead of premium because (in my experience) regular gas has more impurities in it. for instance see http://www.topix.com/forum/city/fletcher-nc/TT5J44OHF9OET25R0#comments. the impurities leave residue in the throttle body, on the valves and in the cylinders.

2) you may want to pull and re-gap the spark plugs. If you are running OEM Iridium plugs it would not be a waste of time to replace them now, with new iridiums or with standard copper plugs. Search 'spark plugs' on this editboard for more on this topic.

tell us more

Albertj

well I put some of that expensive GM injector cleaner in the car (seafoam is a scam) people I have talked to and used it at shops says all it does is burn the fuel a little better. The plugs were replaced about 30,000 miles ago so they are good. The car idles like a worn 4 cylinder Also what is the TB? I work on classic cars so modern EFI, computerized cars are new to me.

Thanks
Josh

When was the last time you put spark plug wires on it? Does it miss on acceleration or only at idle?

I would recommend having the injectors removed, cleaned and flowed. At 191K it's probably never been done and well overdue. It really cleared up my idle. You could also be dealing with a dirty MAF sensor.

I also put some Techron FI cleaner in every couple of months.

It dont miss, it just idles rough when warmed up. I am gussing the injectors need to be cleaned. How many hours would that take to have that done?

I don't know how many hours it takes. I sent mine out to be cleaned and had them back in a few days. I used and highly recommend http://www.codymotorsports.com/

TB is the throttle body. Also check VERY well for vaccuum leaks. A vac leak just might be the culprit if its in the right spot. You should replace the PCV valve also. A few bucks, so its worth it just to rule out that possibillity(sp).

Replace Spark plugs every 30,000 miles. Throttle body torque. Vacuum leaks my hoses were cracked under site cover. Wires especially the ones on left side of engine they get very hot and wear out quicker. Check air filter.

I did not mean the spray-in cleaner, although GMs is better than most. I meant to remove the TB and have it cleaned thoroughly, or simply replace it with a rebuilt one. And I would second the comment about the dirty MAF.

Also might want to take a second look at coils and wires. Plugs don't work so good if the coils or wires are buggered.

Albertj

The shop said while changing my tensioner pully that my motor mounts were worn pretty bad. They think thats why the car idles rough. where can I find motor mounts for the 3.8 and how long do they take to install?

click on dash at top then check out vendors. edmorad is recommend alot around here too.

you can get new motor mounts from gmpartsdirect.com - you will need 'motor mounts' and 'transmission mounts' - - usually the rear tranny mount dies first.

Albertj