Rough idle VY Commodore

[Biggsy]

Got a problem with my car that has always been there since I bought it but haven't bothered to try and fix till now.

Car: VY SS LS1 M6, Stock apart from tune.

Problem:
When in idle, motor has a miss/stumble every few seconds. It doesn't really show in a scan but you sure can feel it.

What I have tried (Not all because of problem):
New Spark Plugs
New Leads
New Coils
New Intake/exhaust gaskets
Std tune, Mod tune, mod tune mafless.
New Battery
New PCM
Checked Earths
Checked for vacuum leaks
Run a cylinder balance check and all are pretty close to each other
Compression check - Good

None of the above made a difference.

If I load the car up, eg A/c on high beams etc, it smooths out the idle a little but nothing to write home about.
Car cruises and accelerates without issue.

The only way I can make it smooth, is to use Bi-Di conrols in the scan tool and command 12.5:1, this makes it idle almost perfect. Wide Band O2 proves it is 12.5:1.

It has me baffled

The only other thing I can think of is maybe blocked injector/s, but I don't want to buy a set and find they are not the problem.

Car has 80,000kms on the clock and has had every service done on time.

Anyone have any ideas?

Cheers,

[JezzaB]

Got a problem with my car that has always been there since I bought it but haven't bothered to try and fix till now.

Car: VY SS LS1 M6, Stock apart from tune.

Problem:
When in idle, motor has a miss/stumble every few seconds. It doesn't really show in a scan but you sure can feel it.

What I have tried (Not all because of problem):
New Spark Plugs
New Leads
New Coils
New Intake/exhaust gaskets
Std tune, Mod tune, mod tune mafless.
New Battery
New PCM
Checked Earths
Checked for vacuum leaks
Run a cylinder balance check and all are pretty close to each other
Compression check - Good

None of the above made a difference.

If I load the car up, eg A/c on high beams etc, it smooths out the idle a little but nothing to write home about.
Car cruises and accelerates without issue.

The only way I can make it smooth, is to use Bi-Di conrols in the scan tool and command 12.5:1, this makes it idle almost perfect. Wide Band O2 proves it is 12.5:1.

It has me baffled

The only other thing I can think of is maybe blocked injector/s, but I don't want to buy a set and find they are not the problem.

Car has 80,000kms on the clock and has had every service done on time.

Anyone have any ideas?

Cheers,

Have you tried changing the commanded base spark idle? If you log it you will probably see when the "miss" appears the timing jumps around alot more. Could try lowering the spark swing (over/under speed correction)

Jez

[Biggsy]

Have you tried changing the commanded base spark idle? If you log it you will probably see when the "miss" appears the timing jumps around alot more. Could try lowering the spark swing (over/under speed correction)

Jez

Yes I did, even when you Bi-Di the spark control to keep it steady, it will still do it.

Even does it with a std tune.

[ntae]

Have you pulled the throttle body & cleaned it ? what are your idle steps ?

[joecar]

Dave, can you run some injector cleaner (the type that attaches to the fuel rail).

[Biggsy]

Have you pulled the throttle body & cleaned it ? what are your idle steps ?

I have not, i'll check the idle steps and clean it 2day.

Lets just assume it is the throttle body.
How come when I command 12.5:1 it idles fine?
How would the throttle body be playing a part in this?

Cheers,

[Biggsy]

Dave, can you run some injector cleaner (the type that attaches to the fuel rail).

I managed to "borrow" a set of injectors off my mates motor, gave them a try last night and it made no difference

[joecar]

Dave,

- how's your fuel filter...?
- how's your fuel pressure (is it constant when the stumble happens)...?
- can you ohm all the plug leads (noting which ohms go to which leads)...?
- when the problem happens, does batt/alt voltage drop...?
- check voltage drop on all ground wires (i.e. from block to chassis).
- check for small airleak at intake manifold.

[Biggsy]

Dave,

- how's your fuel filter...?
- how's your fuel pressure (is it constant when the stumble happens)...?
- can you ohm all the plug leads (noting which ohms go to which leads)...?
- when the problem happens, does batt/alt voltage drop...?
- check voltage drop on all ground wires (i.e. from block to chassis).
- check for small airleak at intake manifold.

Fuel filter is new

Havent checked pressure

Checked all leads, all equal (brand new aswell)

Problem always happens (except when cold and motor is running richer) and batt volts steady 14.1 even when loaded

Earth wires are all good, checked continuity back to batt on each one

I am did suspect intake leak but could not find one, resealed intake manifold. Checked with squirter bottle.

Definatly acting like an intake leak, explains why when richer is being commanded, it smooths out.

[vxchev8]

have you checked the Idle Air Control (IAC)

So there are no vacuum leaks i.e the PCV valve near throttle body.

Try a reset - PCM/Idle learn here cost you nothing