Holden Caprice Rough Idle & Running - Please HELP!!!

[Musti Dilek]

Hi guys

Wondering if anyone can help me.

I have a 2010 Holden Caprice, V6 engine, Petrol

It has a rough idle and now for the last 2 weeks its been running pretty rough also.

I've changed the sparks and the coils as I was told that might be the problem.

Roughness wasn't as bad but now its back to the same roughness.

Changed the oil to a 5-30 Full Synthetic to make sure it's not caused due to thicker oil. Car is currently at 400k. Up until the last 40k it was serviced every 7-10k km's if that makes a difference in diagnosing the problem. I haven't taken it to a mechanic as I've been screwed over by them plenty of times and just do my own repairs now.

Can anyone suggest what might be the problem?

I've been told timing chain, but an ex mechanic mate of mine said, that's not as a common fault as people think it is, as he used to work on Caprice's all the time.

Thank you in advance for any suggestions​

 

[syked]

Have you checked for any vacuum leaks including any loose / broken hoses?

Are you sure that all wiring to the coils are connected firmly?

Is the check engine light on and if so have you had the ECU read with a reader for DTC (diagnostic trouble codes)?

 

[whats up]

 

[krusing]

Has the MIL on the dash come on ? where not all faults will activate the MIL.
What suburb you located in Melbourne ?
If your in southern suburbs, Bayside Area, I could scan it for you, just to see what its doing.

 

[krusing]

As mentioned above about dicey fuel !

Yesterday I had a similar thing happen, engine idling rough and idling faster.
The Last couple of days I have been on the road driving around Victoria,
and been filled up with Shell Petrol 91, and the car has been running and driving perfectly.

Well today I filled up with United Petrol in Hallam in the afternoon on the way home, and the car is now running like a dog,
Idling rough, idle economy is between 2.8 > 3.6 L/100k, I have NEVER seen it idle that high in the 6 years of owning/driving the car.
Where it is usually idles between 2.1 > 2.5 L/100km.
I first put it down to heat, being a 30+ degree day, but I stopped and started the car a few times during the day, and its appears its only started with the United 91 Petrol I put in it.

 

[426Cuda]

Try cleaning the throttle body with TB cleaner spray.

 

[whats up]

As mentioned above about dicey fuel !

Yesterday I had a similar thing happen, engine idling rough and idling faster.
The Last couple of days I have been on the road driving around Victoria,
and been filled up with Shell Petrol 91, and the car has been running and driving perfectly.

Well today I filled up with United Petrol in Hallam in the afternoon on the way home, and the car is now running like a dog,
Idling rough, idle economy is between 2.8 > 3.6 L/100k, I have NEVER seen it idle that high in the 6 years of owning/driving the car.
Where it is usually idles between 2.1 > 2.5 L/100km.
I first put it down to heat, being a 30+ degree day, but I stopped and started the car a few times during the day, and its appears its only started with the United 91 Petrol I put in it.

 

[syked]

Where it is usually idles between 2.1 > 2.5 L/100km.

I see mine idle around 1.6-1.8 L/100km with the aircon on.
Without the aircon it idles around 1.0 L/100km and even seen it go as low as 0.7

I have the LLT engine

 

[Fu Manchu]

I'd take the inlet manifold off.
Clean it out with throttle body cleaner.
Clean the throttle body.
Check the vacuum ports on the sides for looseness or brittle plastic.
Check the PCV hoses for hardened rubber, brittle connections.
Make sure the brake booster hose is a good seal. You can take 15mm or more off with cutters and reconnect to get a good seal.
Put new intake gasket on.
Suss out the purge valve on the side of the engine intake. (They can tick a bit, blow through and check resistance for functional operation)
Remove the PCV valve on the rear drivers side cam cover. Drill out the holes to 3mm top hole and 2mm for bottom 2 holes. Soak in throttle body cleaner. Flush it out with throttle body cleaner, push back in. (I did a thread in How to section)
Clean the MAF sensor with MAF sensor cleaner.
Make sure your air filter is clean.
Remove and clean out the intake ducting with some throttle body cleaner and the hose. Leave it out in the sun to dry out.

Remove the flashing from the exhaust manifold, check for cracks.

 

[Fu Manchu]

The MAF sensor sits in the tube after the air filter.

The purge valve check:
Unplug the purge valve wiring connector.
Using a multimeter (easy to get from Bunnings or Jaycar) test the resistance (Ohms) across terminal 1 and terminal 2. Should read 15-20 Ohms.
Then test for infinite resistance against the housing and each terminal. (not sure about that one because the housing is plastic)

There is the blow through test as mentioned as well.

Holden info suggests one of the first checks for rough idle is removing the O2 sensors and checking for silicone contamination. This will be evident by having a white powdery appearance on the O2 sensors.

The Coolant sensor is also a common cause. If we had fancy diagnostic tools we could see the difference in temp between what the car thinks the air temp is and what the coolant temp is when the car is cold (sat over night). If there is a problem with the Coolant sensor, the fuel trims and timing will be out of whack. These are easy to replace. Cheap to buy. (US Amazon).

The stuff I posted before might sound like a lot but should be done as part of a basic service and would take a few hours to do if you include letting the cleaned out intake ducting and intake manifold to dry out in the sun.