1999 VT Commodore Rough Idle

[N X - X O N]

Hey everyone,

I just bought a 1999 VT Commdore S-Pack as a first car. Recently we did a motor swap out of another VT, and got it start but there is a real rough idle. It idles at about 850 to 950 rpm.

The car has a real rough idle which is noticeably worse in drive or neutral and slightly better in park. It can be felt throughout the whole car and there is a slight ticking after slightly revving it. It also sounds and runs fine on start up but after 30 seconds or so the revs drops and it vibrates.

Symptoms are: Rough idle, slight ticking noise, bad vibrations and possible misfire.

I've changed Leads, Oil Filter, Spark Plugs, Air filter, Intake gasket, Alternator and Battery and it still idles rough, I don't know how it runs when driving as the motor needs to be 100% to get roady.

Any help would be appreciated,
Cheers

Feel free to ask anymore questions.

 

[JohnW]

The 'slight ticking noise' in combination with running rough would have me looking for a high tension lead short somewhere.

Is the engine running on all 6 cylinders at idle? The traditional way to do that would be to have the spark plugs leads sitting just on the end of the plugs (not pushed home), and them lift them clear one at a time and observe the change in engine 'beat'. All 6 should make the same change. Any lazy cylinder will show up as making little to no change.

Now having said that whether its possible to do that with the metal caps on the leads and placement of the exhaust manifolds without burning yourself or getting a decent shock is another question. I've never tried it on a VT, but I'm thinking a set of welders gloves would solve the heat problem.

 

[JohnW]

And .... about the first thing I'd do seeing is an unknown engine being a swap (perhaps you know its history) is do a compression test. With just that one test you can determine the engine basically sound and then spend time on fuel/electrical. Unless you know for certain the basics are solid you can waste a LOT of time unnecessarily chasing the more difficult to diagnose/confirm.

 

[lout]

did you fit new hydraulic engine mounts