So a couple of days ago I found that my TH Exec makes an awful grinding noise when approaching the rev limiter, from about 5k + to the rev limiter. There is no change to the power from the car, just that it sounds okay, makes the noise and sounds shit. Have I broken something? Or is it more likely to be something lose thats vibrating against something else?

Another issue thats been abundant since I got the car is that it idles rough. I've reset the ECU (disconnect power) several times, no fix. If I am at the lights in drive when the engine is at operating temp, then it will idle around 500rpm and the whole cabin vibrates. If I drop it to neutral or park it becomes less noticeable. If I rev it up a bit it goes away. Occasionally it is solid vibrations, other times it sort of randomly vibrates. Eg, duh duh duh duh versus duh.. duh duh duh. duh duh... duh... duh duh.

Kind of harder the last one, I'm thinking it might be something to do with the idle speed control, or something?

Defintely start by cleaning out the throttle body and ISC. I've got a rough idle I'm trying to get to the bottom of but cleaning out the tb & isc has helped a fair bit. Still not perfect but much better.

Get some new gaskets & o-rings while you're at it. I'd used a rag and some carby cleaner. Worked the charm. Clean out every nook and cranny. Will make a difference. Hopefully it'll fix your idle issue. Otherwise it might the leads, dizzy or even the O2 sensor. So far these are the three causes I've identified that give people grief on idle.

how loud is the grinding noise? can you describe it better. as for the idle, that willl likely be a seperate problem, one that is common to magnas, i have never had it with my jdm diamante, but i had a 3.5l Diamante sei (adm verada) and at idle in drive it would idle low and shudder lightly, i replaced the dizzy, plugs, leads,gaskets, cleaned everything, the lot and it still idled low. my jdm car has coil on plug ignition and doesnt do it. im sure its a design issue.

How much of a flogging do u give the car? Too much time in the red line perhaps?

First thing I'd check is the engine mounts, one or more could be split/cracked?
As for the idle, as said above, ISC, check leads, dizzy etc, don't rule out spark plugs either maybe check the front 3. Do you know when fuel filter was replaced last? Does it use much fuel, run rich etc?

I did hit the limiter the other day. Driving on hills, slid it down to first and stayed there a tad too long. Did I break something?

I did hit the limiter the other day. Driving on hills, slid it down to first and stayed there a tad too long. Did I break something?

you might have but i would not know for sure you would need to go over your car to see if any thing has broken / as for idle you need to do a base idle reset each time you disconnect the battery you need to do this if you are over near chadstone way at any time during week in the afternoon after 6 pm or on week ends any time i could help you out with that idle problem and have a look to see if you have done any of the mounts cheers liam

The noise is sort of a vibrating noise, halfway between vibrating and possibly metal on metal scratching. Sorry I can't be more descriptive.

I'll give the ISC and all that a big cleanout tomorrow.

Anyone got any possible suggestions on what physically might be making the noise? What moving parts are most succeptible to vibration/movment to cause noise at high RPM speeds?

could be a lot of things could not say for sure unless i heard it is this noise all the time or only just when you are running the car hard near red line

Well, I took the intake snorkel assembly off and cleaned the throttle body and ISC with some carby cleaner. I can't notice much of a difference unfortunantly. ALTHOUGH, the noise has gone! For now, atleast. It must have been something to do with the assembly.

Rough idle is still there. I'll have to have a look at the mounts.

I also had a look at the engine bay when it was idling, and from what I can see, the engine shudders, in a non-linear (meaning, the shuddering doesn't happen to a pattern, it shudders randomly every second or less) pattern. Are these symptoms of maybe a spark plug not firing properly? Maybe firing every second or third time?

This, and maybe the harmonic balancer? Would that cause this?

Have a look for air leaks or loose vacuum hoses, normally thats the reason for unstable idle.

Check your harmonic balancer pulley BOLT ... mine came loose , caused the timing belt sprocket ( located to crankshaft ) to wander , which in turn causes the crank Angle Sensor disc to flutter off the back into the CAS Sensor ( mounted at the bottom by the crankshaft ( on the oil pump housing ) . Check the Pulley bolt - mine came loose enough to completely disengage the pulley from the crank , prior to this , missing engine , and rattling scraping sounds .