Intermittent engine stutter - coils plugs and leads replaced.. what next?

[eddyvr4]

Hi all, looking for some advice from some of the more mechanically experienced members here

the symptom is an intermittent stutter that sometimes occurs as a single jolt on light load, just off boost. and also very occassionally series of jolts under full load. its not a savage stutter like a boost cut but very noticible even by passengers.. like its dropping a couple of cylinders. it can run for 50 or 100km no problems, then do it a couple times, then fine again for a while.. its most consistent on light loads after idling or coasting for a while, but occasional under full load like overtaking. on the whole the car runs fine, but its an irritating issue i cant seem to iron out.

VK22 plugs are between 0.7mm to 0.9mm gaps and all look the same and ok (10,00km old or so) , all 3 coilpacks are almost brand new and the plug leads are ICE units and less than 20,000kms old. (and measure about the same DC resistance each)

compression is good and even on all cylinders. (injector seals have been done)

ive nipped up earthing points on the engine and wiggled plugs on the coilpacks at idle.. (it has an earthing kit fitted from japan) no oil leaks into the spark plug holes.

sometimes it does idle a tad rough in traffc (just a bit more vibration than normal) no hunting or stalling etc.

could it be a fuel delivery issue and how best to test that?

It does feel like a problem on the high tension side but ive replaced everything..

no error codes are logged.

any other ideas? any help would be much appreciated..

 

[AKKO]

Hmm stock or aftermarket fuel pump... maybe MAF, running stock snorkel or pod filter?

 

[eddyvr4]

its a walbro pump .. stock MAF and airbox/filter...

 

[trotty]

How old is ifs module. Top of front rocker cover?

 

[eddyvr4]

its the original one.. hmm.. something to think about.... thanks..

 

[uzz320]

Running stock boost?

 

[TME_Steve]

fuel filter?

 

[naughtika]

played around with your TPS?

 

[eddyvr4]

Thanks All..

Its Running about 14psi, but it mostly hesitates off boost.

is that the in tank fuel filter or is there one under the bonnet? because its such a sudden jolt and goes away so quickly and happens under low fuel use (low load) , fuel filter just seems like a long shot.. but yeah..it could be an intermittent fuel pump.. electrical problem in the fuel system maybe..

regarding the TPS because the car runs fine 99% of the time im sure if i do a static test it would measure fine..

i read elsewhere about a panel filter disintegrating into the MAF and interrupting the MAF signal... mine is a stock filter but ill check that anyway..

Thanks Guys.. any other suggestions welcome..

 

[AKKO]

Stock paper air filter, how old... assume it's clean?

Best start eliminating some stuff before everything under the sun is listed here as possible fixes. ;-)

 

[mcs]

fuel filter is driver or passenger side rear ( someone else can clarify which one ), just on the other side of the sill under rear door.

Cheers Mark~

 

[Yo_Mang]

Also maybe try giving the MAF a good clean. Mine was playing up a bit like your symptoms and after a clean was fine!

 

[TME_Steve]

Fuel filter is under the drivers side rear door, but if it's only off boost that it's a problem....

Meh, take it to Jon

 

[Dice]

Could be IPS/TPS since it occurs during light throttle. With a faulty IPS revs can drop quick enough to jolt the car (almost like boost cut) when it believes you're in idle. E.g. going from full throttle to no/light throttle at which point the idle position sensor erroneously engages.

 

[uzz320]

I would recommend returning the boost control to stock just to rule that out (it's free and quick to try) - I had almost identical symptoms when I first got my car a few years back, and changed the fuel filter (didn't help) and then later changed the spark plugs to VK22s, the coils to COP, the fuel pump to a Walbro 255lph, the boost control to a 3 port and had it tuned by TME_Steve in one week and it hasn't happened since - so one of those things fixed it. Also definitely didn't have any boost leaks at any point.

Mine seemed to start with high load stutter on a small percentage of trips, and as the trip went on it would happen at progressively lower loads (or so it seemed). It probably only happened on 5-10 occasions over a month or two, but was often enough that I was sure it wasn't going to go away by itself.

 

[trotty]

Could be IPS/TPS since it occurs during light throttle. With a faulty IPS revs can drop quick enough to jolt the car (almost like boost cut) when it believes you're in idle. E.g. going from full throttle to no/light throttle at which point the idle position sensor erroneously engages.

This is exactly what mine does under light throttle. I'll be creeping slowly in 1st/2nd gear and as soon as I lift the throttle it's like I've lifted right off the throttle and jerks quite bad in traffic.

 

[vr4cobra]

mine does similar to hmm

 

[AKKO]

Tested for boost leaks?

 

[Dice]

This is exactly what mine does under light throttle. I'll be creeping slowly in 1st/2nd gear and as soon as I lift the throttle it's like I've lifted right off the throttle and jerks quite bad in traffic.

You probably just need to set up your tps correctly.

 

[naughtika]

found that sweet spot for TPS is 13.7% (done this on Dan's car)

originally thought 11 or 12% but car goes into stall mode then goes back into normal idling after..