Mild Stuttering while cruising

[Malcster]

Seems to be a bit of a strange one...

While cruising, just maybe a touch of throttle, 2,100rpm, 5th gear, 70mph or there abouts, and it'll stutter mildly.

Totally clears if you open it up though.

I changed the dizzy cap, rotor arm, leads, and plugs, checked all extenders too - no issues, still stutters.

Any ideas?

[Dr Mike Oxgreen]

Any other symptoms? What about full throttle up to 6000 rpm - pulls smoothly, or not?

My instinct is that it's not typical of the coil breaking down - that usually gives symptoms first at higher rpm, where the ignition system is working much harder.

If it only happens when the throttle is only slightly open and the engine is spinning at moderate to higher revs - i.e. when the induction system plumbing is under considerable vacuum - you might want to consider an induction leak perhaps?

[Malcster]

Yeah, only ever part throttle, I.e. get up a cruising speed in any gear, then only give enough throttle to keep it ticking along at that speed.

Full throttle at any point, to any revs clears it.

Nonissues full throttle to 6k, but if I backed off and held it with a feathering at say 4k, it would likely stutter.

Forgot to mention I'd changed the coil as part of a service too.

Haven't changed the ign amp.

I'll get the WD out and check for air leaks.

Any tips on where to look / usual suspects?

[ButtonIt]

Any joy?

[taylormj4]

Throttle position sensor ?
Have you got Rovergauge ?
If yes, check that there isn't a bad spot on the potentiometer track by gradually opening the throttle and seeing what reading it gives.
If you haven't got RG, you can also do this with an ohmmeter.

[Malcster]

Havent had a chance to check for air leaks yet.

Any specific places to try? I'm just guessing all rubber hoses entering the plenum?

Thinking back, I'm sure this started happening just after I used a tank of crap fuel. Maybe just coincidence?

[silverback mike]

Soapy water on intake hoses to check for leak but my money is due to fuel, new filter, injector cleaner and

[Malcster]

Well, no luck with the induction leaks into the plenum, as far as I could see.

It's also had a new fuel filter. I've now bought a couple of bottles of Redex for the hell of it, I'll dump them in the next few tanks of fuel I buy - see if that has any effect. Hardly a big expense - £3 a bottle.

I'm guessing you're not meant to mix additives with pre-additive fuel? (I.e. V-Power)?

[ButtonIt]

How does the soapy water trick work? I need to check this on mine...

[s p a c e m a n]

Loads of fairy liquid in water makes bubbles over any leak. It's impossible not to turn into a child and start blowing bubbles though, then your neighbours look at you like you're a nutter

[ButtonIt]

Surely the engine is sucking it in though?