Occasional Miss Or Lump On Idle

[sturb25]

My car has this wierd occasional miss or lump as some people call it on idle. It doesnt effect my engine rpm, it may if i put it on a dyno with an accurate rpm gauge but i dont see mine on the dash move at all. Neither does the boost/vaccum gauge move, but you can feel it through the floor.

It doesnt effect it at all in anywhere in the rev range just on idle sometimes. It hasnt done it for a while but when it used to do it i changed fuel for Caltex vortex 98 to BP ultimate 98 and that fixed it so i pressumed it was the fuel but its come back in the last couple of weeks.

Its feels like a dirty injector.

Just wondering if anyone can throw a few suggestions at me to help me get it sorted cause its probably nothing thats going to do any harm but its kinda anoying

Thanks

Stu

[180fan]

Mine does that as well, exactly the same thing as you described. It doesn't happen that often though.

[d1_drifter]

Mine used to do that, but it's not there anymore haha.

Mine would idle fine, then all of a sudden sound like a cylinder didn't fire, then idle fine after. Pretty sure it went away after putting in some new plugs.

[Stagea_Neo]

had this on my r31, new plugs fixed my issue.

the stag does it rarely, so time to check the plugs ...... when i pull my finger out and get motivated.

if that dont fix time to check other ignition parts/loom.

[Big Jim]

good call on the plugs

they are the hards working part on any car

[V28VX37]

Might also be ... tada! ... the coil packs.

If changing plugs doesn't fix it and you're still running original coils they might be worth a look.

[kidafa]

Its not noticeable in the car but if you stand near the exhaust or outside it you can here it miss once in a while? Ive just realised mines started doing it going to plug into consult so I can watch the RPM and see whats going on. TBK only thing I can think of that would be causing it for me is the plugs as I've not to long ago changed from gold series to the cheaper BCP6RES's @ .8mm

[wolverine]

My RS4S does the same thing.

260 deg poncams are the cause.

Mmmm lumpy.

[RubyRS4]

Might also be ... tada! ... the coil packs.

If changing plugs doesn't fix it and you're still running original coils they might be worth a look.

Check the CAS timing first. Thats free.

Then check you have no lose clamps under your bonnet leaking air ... especially the smaller vacuum type hoses. The ones under the crossover pipe do tend to split over time. This check is free too.

Then try giving your AFM a clean. Especially if you run an oiled filter.

Then try replacing your plugs. Gap them to 0.8mm.

Reset your ecu too.

If the problem persists, the consider replacing your coilpacks, and even your O2 sensor.

[V28VX37]

Check the CAS timing first. Thats free.

Then check you have no lose clamps under your bonnet leaking air ... especially the smaller vacuum type hoses. The ones under the crossover pipe do tend to split over time. This check is free too.

Then try giving your AFM a clean. Especially if you run an oiled filter.

Then try replacing your plugs. Gap them to 0.8mm.

Reset your ecu too.

If the problem persists, the consider replacing your coilpacks, and even your O2 sensor.

Spot on, OP take note.

RubyRS4, been there done that, thanks for the tips though

[RubyRS4]

Spot on, OP take note.

RubyRS4, been there done that, thanks for the tips though

No worries

I've learnt most people go straight for looking for a leak on the bigger pipes (fmic and hoses). But the little vacuum lines are brittle over time and can crack and leak, and cause just as many headaches hunting down.

Oh, and if you ever get the chance, give your idle control valve a good clean with carby cleaner too.

And, lastly, ensure nothing 'rubs' against your fmic, as this can cause a "hard to find" leak also.

[kidafa]

rolled into uni a bit early so sat in the carpark with piggback in hand wathing digital RPM read out. Car drops 30rpm at the most when it makes the noise analog gayuge doesnt move at all and you cant feel it through the car you can just hear the exhuast change for a split second.

Will check what roo's said when I get a chance...

Need to iron this out change rocker cover gaskets and half moons new oil and filter and then time to a tune and see how much the manual conversion has changed things.

Edited August 12, 2010 by kidafa

[chuckie]

Hi Maybe Coilpack`s,

Put AC on & see if it make`s it worse ,then start looking at which coilpack is the problem.

Goodluck,

Cheer`s Chuckie.

[sturb25]

Hi Maybe Coilpack`s,

Put AC on & see if it make`s it worse ,then start looking at which coilpack is the problem.

Goodluck,

Cheer`s Chuckie.

cant be coil pack, replaced them about a year ago with spitfires. will try everything else. firstly plugs

[Duncan]

my bloody race car does the same thing at idle...always has and everything except the loom has been changed over the years. runs fine above idle though so it's never worried me too much.....

[RBJETT]

my missus' rsv has the same problem. shits her to tears nearly. im a mechanic, and it never happened with me in the car until just last week. seems that her car also shudders, feels like an occasional miss only when not under load at about 500rpm. but my understand was that the car couldnt idle that low. gonna reset the ecu and check out her coilpacks to see if that solves it

[lachlanw]

take your afm off and hose clamp a pineapple can in it (or what ever fits ) and pull a vacuum line off something and pump entire intake system up to see if anything is leaking . can monitor pressure on boost gauge

[kidafa]

So I had a go at chasing my slight miss on idle today, with no avail.

I pulled all plugs and checked them out and coil packs

Pressurised intake system to check for leaks with no signs except rocker cover gaskets

Replaced rocker cover gaskets and halfmoons

Cleaned airflow meter

Cleaned throttle body

Im going to clean the AAC valve when i get a chance and plug in the laptop to double check 02 voltages for correct operation. Apart from that im kind of stumped. It doesnt miss behave at all otherwise on a tiny bit at times on idle, can bearly see the change in rpm on the dash can only here it in the change it zhorst note or if you look at the digial rpm read out.

Need to get this shit sussed so I can get on the rollers and get a tune and see how many ponies ive got going on after the manual box and wind up of a few more psi

Anyone got any ideas?

[lachlanw]

maybe reset the sels learn in the ecu . or plug in someones laptop to it and turn off spark to each cylinder and seeif you can locate it to one cylinder.

or check o2 sensor readings

[kidafa]

Ill reset self learn.

Ive got daignostic stuff for the laptop. 02 Sensor appears to be doing what it should.

Ill turn off a cylinder at a time but i swear the miss isnt that bad that its a cylinder down or anything if that makes sense