Very slight misfire whilst cruising

[mattblack_lude]

OK guys abit of an odd one here,

I've noticed the puma feels like its got a very slight miss when the throttle is lightly applied (maintaining speed) say in a 30/40, for example.
It doesn't sound like it had any running issue when on idle, nor on full throttle. This seems to only effect it whilst the loud pedal is positioned to maintain a speed.

A general misfire would lead me to change the plug, leads, and probably coil pack. But a misfire, only under the above circumstances? I can't figure it..

Is this a common issue, with say, a bad coil pack? Im giving it a mahoosive service in a weeks time (oil, oil filter, air filter, fuel filter, gearbox fluid top up etc) but i haven't yet allowed for HT leads or coil pack. Should i?
Im aware the inlet manifold has a sensor on it, and also lower down another (throttle position sensor?). Are these worth taking out and cleaning? Im guessing the one on the body of the inlet manifold can be cleaned, not sure on the TPS. Also, MAF? I've seen that crop up more than once as a commonly failing part.


Any help would be greatly appreciated, its not currently the end of the world, but its there, and its annoying to know its present.


Thanks in advance :grin:

 

[mattblack_lude]

Actually, this morning i held the revs at about 1500rpm and noticed the hesitation is there, and also even on idle. Its so slight that you could mistake it as nothing, but you can feel & audibly hear the rev difference whilst idling. The needle does move ever so slightly aswell, so it must be fluctuating by around 100rpm either way.

Hope this helps somewhat....

 

[quest63]

It cant do any harm to clean the idle control valve and MAF and the area around the butterfly in the throttle body its only a couple of quid for carb cleaner.

Check the black rubber nipple on the front of the inlet manifold isn't cracked or missing.

 

[TGPlayer1]

Also check vacuum hoses. There's one hidden under the inlet manifold that has a T-piece in it, it's to keep the crankcase under vacuum. The oil degrades the rubber over time and they split, which can cause bad idling and cruising. I know this because one of mine collapsed on itself and when I opened it up the engine spluttered and tried to conk out as it lost crankcase vacuum.

 

[mattblack_lude]

Superb, thanks for the suggestions guys.
I'll be working on the old girl and will check out the above points with carb cleaner in hand.

Cheers :wink: