VS V6 Berlina - rough after start but quickly clears | possible increased fuel usage

[LXCHEV]

The daily driver has recently developed a new, minor issue:

VS V6 Berlina - stock as a rock.

Turn the key and start it up, not a problem - but then for the first few seconds it idles as rough as anything, before quickly settling down and then behaves perfectly normal. Drives great. Having said that, I've also observed 2 other things that are very likely related-

1. Fuel usage has increased (would normally expect 15-16L / 100km for the local train station trip) - now seems to be more around 20L / 100km.
2. Black soot/exhaust splatter can be seen on the wall behind the tail pipe (clearly running rich) - or at least was at some point in the recent past.

Just throwing this out there in case anyone has experienced similar symptoms. Otherwise, I'll have to begin the troubleshooting / process of elimination.

Cheers,
Brett.

 

[ephect]

Going to say your lower intake manifold gaskets are shot. Excess water out the tailpipe, and stumbling as it clears the cylinders. Check your water levels in the overflow and rad to see if your losing water

 

[knos]

or leaking injector, when left for long periods could fill the cylinder then when started it would send it through the exhaust..

 

[LXCHEV]

Cool, couple of things to check - cheers. It’s never used water previously but will have a look to see if anything’s changed. Injector one is interesting.

 

[Gus The Snail]

or leaking injector, when left for long periods could fill the cylinder then when started it would send it through the exhaust..

Usually your oil starts smelling like fuel when that happens, so wouldnt that be a place to check? Pull dipstick and have a sniff to see if it smells like oil, or fuel soaked oil?

 

[Immortality]

stuck/leaking injector is a a real possibility.

So is a tired ignition system not firing properly. Check plugs and leads for starters, have a good look at the coils too, with age they can crack (especially if you have washed the engine bay).

 

[LXCHEV]

Just a follow up on this one. I gave the car a good service and actually discovered a couple of interesting things here.

Firstly - I threw in a fresh set of plugs and a new set of leads. I had replaced all 3 coils several years ago, but they weren't a matching set. As I replaced the leads, I noticed that 1 coil had slightly dirty/rusty posts, whereas the other 2 coils were mint and still shiny as new. So whatever material/coating they used on those coils was much better than the other one (can't remember brands unfortunately). Not something I would ever have thought to proactively check. For now I've just cleaned the posts and smeared on a tiny bit of dielectric grease which should stop them from going bad again. Will be something I keep an eye on though. The car was still running well and certainly not missing, but perhaps this was contributing to my issue.

Second thing I found - I noticed that my temp gauge on the dash wasn't reading. I removed the connector to the temp sender on the engine and re-installed, then repeated a couple of times to clean the connection. Problem solved. If that was stopping the gauge from working, then I assume the ECU wasn't getting an input from that sensor either? So again, another possible cause.

I've also cleaned the throttle body, IAC and air flow meter (always do these 3 items at the same time as the main service). Threw in a new air-filter for good measure too (old one was actually quite filthy). Then all the usual oil + filter change etc....

So far so good - car is behaving normal again, feels good and fuel usage certainly appears to have come right back down again. Just need to get a bit more driving in.

 

[Immortality]

Good to hear it's sorted.

The dash and the PCM each have their own temp sensors. Single wire for the dash gauge ,2 wire sensor for the PCM (under the thermostat housing).

 

[vr304]

I’d chuck some lucas injector cleaner/ upper cylinder lube in for good measure too, it’s really good stuff

 

[LXCHEV]

I’ve often wondered about injector cleaner. What’s been your personal experience with it? I do like the idea of the upper cyl lubricant too - anything that helps to reduce carbon buildup.