...MiSFiRE ON iDLE

[XRUFFX]

another small query guys...
my car misfires on idle, u can jusssst here it in the background of all the other other noise...the set of spark plugs i had in before these had been misfired on so, i thort if i change them it might help, so i did that, and it worked for the first time i let it idle, then next time i drove it and got out and listened, it was doing it agen....wat might this be?
it doesnt mis AT ALL at any other time....the engine is sound...no leaks...no funi noises, no lack of performance....

 

[Haydz]

have you replaced the leads? also could also be a faulty coil in the coil pack.

 

[XRUFFX]

yeah leads and plugs were all new....if it was the coil pack wouldn't that make it a permanent problem not just on idle? altho i have no idea as to the age of the coil packs...could b a thort

 

[johnnyk]

Grab a multimeter and check the resistance on all your leads (just in case)... check the gap on your spark plugs. See how you go with that

Also, check the leads are going to the correct plugs. When did it start happening?

 

[XRUFFX]

hrmm ill have to borrow a multi off a mate lol um, its hard to say wen it first started, i have a feeling it started wen the plugs were replaced the first time...i just dont understand y it doesnt do it under load but on idle...my mate made the leads, but thats not to say i wont check em lol wats the easiest way to check spark plug gap..? (if thats not a stupid question) leads are def in right spot also....well according to the numbers...
also its weird that it stopped wen i replaced the plugs cos i thort it was the fact that theyd been misfired on cos of faulty leads, and with the new ones, it stopped, but wen i drove it for the second time it started again...

 

[kopper69]

Probably not the leads. If it was the leads they would normally play up all the time if they were faulty or under load if the insulation was breaking down. To check the spark plug gap you need a spark plug gap tool or wire gauge. I have found that the leads that I purchase from supercheap for my VR, think theyre bosch? are already gapped and dont need any adjustment. If you overtightened the spark plugs you may have cracked them which could cause problems. Probably not the leads though if the leads are fairly new.

Your fault may lie with a vacuum hose or IAC valve. The IAC valve controls the idle - if that was sticking you would obviously get a funny idle. Check all the vacuum hoses around the throttle body and check for error codes, could be a sensor giving a funny reading that you may have a error code logged for.

 

[Cheap6]

If it's at idle only, it's probably a vacuum leak; as the throttle is opened the vacuum in the manifold is reduced and the effect goes away.

Maybe the inlet manifold gasket has lifted due to corrosion around the water passages or maybe an exhaust valve is leaking.

 

[Chirpstr]

Did you remove your Bellmouth?

 

[XRUFFX]

um well, the inlet mani gaskets r brand new....ill check the hoses around the throttle body, and yeah Wavez, i did remove the bellmouth, can that cause issues?

 

[Chirpstr]

yes it will cause rough idle. (that's the down fall) They put it in the Buick motors to improve idle. I'm going to cut mine in the center to make a U and see if my idle gets a little better if not I will just get another one from wreckers and wack it in how it's meant to be. When I removed it I noticed the idle was lumpy straight away. (Poppy) It made the accelerator more responsive though...The buick motors you can never get a perfect idle...they are well known for this.