VX LS1 1000-3000 RPM / shuddering issue

[matt123776]

Hi all,

Hoping one of you may have some ideas as to the problem I am having with my car...

Basically, when starting the car each day or after an extended period of rest, my VX is shuddering between 1000-3000 RPMs. While it struggles to get moving, there is a clunk or two but then the car decides it wants to run. After that doesn't seem to clunk or shudder much if at all. Occasionally the check engine light appears but can still run fine, other times feels like it wants to collapse in a heap. The light isn't always on and only sometimes appears.

Since happening, the fuel filter has been changed as have the plugs, the leads appear fine and are about 40k old. In addition, an on-car injector service was done yet still the same. I took it on the M5/7 yesterday for about 50km and no such issues so only seems to affect low RPMs when commencing a trip. Idle occasionally feels rough when sitting at lights but doesn't quite stall. Mechanic said no fault codes have registered and the issue has him stumped. He suspected dirty fuel but after running BP ultimate through it the past day or 2 the issue is still there. He hasn't suggested a rebuild or anything expensive so I have no issue that he may be misdiagnosing something that doesn't exist.

Car has extractors, high flow cats and full 2.5 twin system. It's been on there for a year or so and the issue has only come up in the last couple of weeks. It's worth noting that the car will sometimes run fine with no issue at all.

Any thoughts suggestions would be appreciated.

Cheers

Matt

[matt123776]

Okay so haven't updated at all.

Took the car to have a scan done today as I didn't think the mechanic looking at the car did actually do one. The scan returned 5 faults. 4 of the 5 related to the oxygen sensors the other was a transmission B solenoid. The AE thought the Oxygen related would be from the extractor install but wasn't sure about the other. He noted the codes down then wiped them and then re-tested and nothing came up. He took it for a test drive and as expected no issues. I left and the car was running like crap again but no engine light this time. I did some research and found out that both issues could result in the car switching to limp mode which may explain the sluggish feeling.

Anyone else experienced anything similar? Car still clunked when first driving to the AE but not after that.

[Richie217]

What was the auto error code? I had a code for the trans pressire manifold being faulty a few months back. Basically the car was just shifting very harsh, but other than that the car drove normally. The drivetrain warning light would come on once the trnas flyid got hot, I assume the temp would alter the pressure. Had the manifold replaced and all was good.

If the O2 sensors are on the way out I believe that would make the car run poorly and idle badly.

[matt123776]

thanks for that. Code I received was PO756 which related to solenoid B. The other 4 codes were for left and right oxygen related banks PO134,154,172,175. For the cost of a new set I think it's probably worth doing them anyway.

gear changes seem smooth other than during the clunk/shudder while revving high enough to get into 2nd.

[matt123776]

So took it for a drive again today to top up the petrol after not driving it much and feels worse again. Took off not too bad but definately under normal power, took a left and barely wants to move then some of the clunk/banging noise then eventually feels like it surges. Only seems to be affecting down low. Haven't done the o2 sensors as no lights have come on since having the first scan done. Would have thought that the check drivetrain light would have appeared again if it was the solenoid or o2 issue that the scan initially pointed out.

Might have to just take it somewhere else and get them to nut it out. I thought maybe leads as it does feel like a bad misfire but having had the plugs just done, surely the mechanic would have noticed an issue there. The eagle leads are about 50k old. Failing that maybe the coils.

Any thoughts appreciated

[matt123776]

Hoping to sell it in the next couple of months so want to get it all sorted before then.

[Cameron P]

I would start with leads as they are obviously over due then do the o2 sensors.. If the issue is still there then the auto trans has an issue

Always start from cheapest to expensive to find the issue

Good luck mate

[matt123776]

So it seems I may have sourced the issue myself.

I paid $160 to have the spark plugs replaced and what do you know, the "mechanic" has replaced driver side only I assume as the first plug on the passenger side was still the old rooted NGK I had put in 50,000 ago and not the fresh shiney ones supplied. So effectively I am driving on what I can only assume is 4 new plugs and 4 rooted ones which could explain the misfire.

Plus the gaps on the new ones is about 2mm which seems a bit much.

[matt123776]

I can only assume he thought I wouldnt be able to check due to the narrower passenger side.

[Cameron P]

Take them back to him! And say you want everything replaced as other items could have been charged to you but not replaced!!