Reasons Why A Car Runs Rough?

[SS8_Gohan]

Hi everyone,

just wondering what are the main reasons a car can run a bit rough, especially on idle?

i've recently replaced both coilpacks (to Splitfires) and spark plugs (to NGK Iridiums) on my 34 and i noticed on idle it's still running a bit shuddery, i guess the best way to explain it is that when you're cold, you sometimes just shiver, well it feels like the car will just shiver/shudder every now and then on idle...

sounds a bit noisy (i know, very vague) when driving as well, are RB engines on the noisy side? grown up with BMW inline 6's, and they are smooth as anything so that's my comparo engine type.

Car has 51,000km's on the clock, no idea of validity of that (98 Car) - don't think timing belt has been changed.

Car ran for a short time on 5 cylinders, when one of the coilpacks died. So i've been told that the fuel would have been going around that cylinder and could potential wear off the oil, etc... not sure.

Don't think has had oil change since compliance (bout 2,000km's since compliance) not sure if they changed it though.

Just wondering what are the main reasons a car would be a little rough running that's all?

cheers,

daniel

[Mr Italy!]

Do a 100k km service on it.

Do everything that you should have done when it first arived. Engine, gearbox, diff oils, all belts etc.

Just do it for peice of mind. If your still having trouble after that, then come back and ask whats going on.

[SS8_Gohan]

well it had a semi-service when i got the road-worthy - i asked the guy to check oils/filters - he said filters were fine, oil was not too bad, he said maybe 1 month get it changed. I don't know if you can check belts?

and since then have now got brand new coilpack and sparkies - i'll have to double check what the compliance place did.

so it's been looked at and such but i suppose you never really know the km's...

i've also been told that changing oil won't make a car run smoother, or cause it to be rough?

[Mr Italy!]

My car pops every say 20 seconds when its idling, nothing too major, just a bit of a pop. I dont really care about it as its just a slight missfire. My mates R33 does it to...

If thats all you're woried about then you've really got nothing to worry about.

[ToF]

My car pops every say 20 seconds when its idling, nothing too major, just a bit of a pop. I dont really care about it as its just a slight missfire. My mates R33 does it to...

If thats all you're woried about then you've really got nothing to worry about.

Mine does a slight misfire on idle every 5 seconds. Only started happening after I had problems with a coilpack (fixed now). It doesn't misfire once its off idle.

I've decided to just ignore the problem, but I wouldn't mind trying something if anyone knows how to fix our problems.

[Konrad]

I too have been chasing this problem as i thought it to be coilpack related. I've changed plugs (ngk iriways), splitfires, taken off the afm, throttle body and ISC valve and cleaned them to no avail. The only thing left for me to do is get the injectors cleaned ultrasonically, change the fuel filter, double check my timing at idle, and change the 02 sensor, which i'm hoping is the culprit - i've been told the 02 sensor controls rpm at idle, not the afm.....

[666DAN]

Give the AAC valve a clean, the R34 type uses a vibrating stepper motor to adjust the airflow, my one seized shut with dirt and bollocks a while back, that led to a constant high idle.

Also having the A/C on for a cold start gives me a feeling similar to a dodge coil-pack when it first runs in the morning, once all warmed up it stops...try running with climate control off and see if it's fixed.

[LatinR33]

Maybe faulty tps could be a prob aswell

[SS8_Gohan]

faulty tps? what's tps?

no exactly sure what some of these aac/isc valves are etc, but it's all noted.

O2 sensor... well it's easily done more than 40K

in regards to the "popping", i've had the car parked, bonnet up, just to have a listen and every now and then, maybe every 15-20 seconds, i'll hear a 'pop' i guess is the best way to describe it. you can't hear it from the inside with the doors closed, but with the bonnet up you'll hear a pop, sounds like it's coming from the back of the engine bay, not 100% sure. It's probably not really a pop, but like when you turn a gas stove on and you hear the ignitor going, 'tick' 'tick' 'tick'... it's kinda like 1 of the 'ticks' and that's it... because i'm not in the car at the time, i can't tell if the car shudders when it 'ticks'...

*sigh* i dunno.... i'm annoyed i don't know how to check/do all this stuff myself, need to know more about engines..

[Craig Baxter]

tps = throttle position sensor, tells computer the percentage of throttle applied

popping = missfire, most probably a spark issue - plug or coil, check gap and also for cracks in coils, if there is any cracks cover them with araldite and allow to set, araldite does not conduct electricity or alloy it to pass, much better fix than the tape most people are using. (my friend who is a mechanic thought of this and fixed his coilpack problems on his 1jz soarer) mechanics are great friends haha

if it is more an unsteady idle probably be stepper motor, clean it and see, also take the throttle body off and clean the throat and butterfly and all passageways with throttle body cleaner/carby clean (careful with carbie clean make sure it is throttle body safe some etch away at the alloy) my car was really rough at idle and cleaning these parts fixed it. hope this stuff helps.

[SKY031]

well it had a semi-service when i got the road-worthy - i asked the guy to check oils/filters - he said filters were fine, oil was not too bad

I'd love to know how the mechanic managed to check an oil and/or fuel filter.

They are both sealed, non servicable parts.

Time to find a new mechanic.

[Green_s13]

i agree with sky031 about going to another machanic. on top of what craig as said about throttle body cleaning i woudl also have a look at the AFM i have had these affect the idle of cars before

[SLIPPERY]

I'd love to know how the mechanic managed to check an oil and/or fuel filter.

They are both sealed, non servicable parts.

Time to find a new mechanic.

perhaps he checked the oil by pulling out the dipstick to look at the colour and possibly the smell of the oil to determine its life

[Nozila]

if it is more an unsteady idle probably be stepper motor, clean it and see

location of stepper motor would be much appreciated