Revs dropping in and out

[GFro93]

My Chim currently starts and idles no problem, but as soon as I put my foot down in 2nd or third (havent tried higher) the revs jump up and down and the car jumps and jolts as if I am stamping up and down on the accelerator.

I have previsouly had an issue that was down to a bad earth but had that fixed and drove a 300 mile trip no problem. I have replaced HT leads, Dist.cap and rotor arm (twice). Am at a bit of a loss where to go next with it...has anyone else had a similar issue?

[ginkent]

I don’t have a chim, haven’t a clue on anything mechanical or electrical, but I’ve read enough posts here to suggest the problem likely to be a bad earth.

[FunkyGibbon]

I've had this. Turned out to be as simple as the air intake pipe to the AFM wasn't connected fully.

Hope yours is as simple.

[frontfloater]

I had a similar problem on my S2 a few months ago, happening at random during otherwise smooth motoring. XWorks diagnosed it as a faulty coil.

[ez64]

Had this problem as well and it got worse. Mainly it was the throttle pot sensor wiring that sits in the V of the engine was wrecked. I ended up cutting it out then replacing the wiring and replacing the throttle pot sensor which solved the issue although replacing the sensor was expensive and probably not needed.

Worth testing the sensor with rover gauge and while you have the car on ignition 2 watch the throttle percent value smoothly climbing and falling as you move the throttle by hand in the engine bay. Also helps to have someone wiggling the wiring while doing this and see if you can get intermittent results which confirmed it for me.

Other places worth checking are your main positives and grounds to make sure they are not breaking free with the acceleration of the car.

Edited by ez64 on Friday 14th January 17:43

[Belle427]

Sounds like misfires to me.

[s p a c e m a n]

Weird that it only does it under load, there's no sign of it if you just rev the engine when stationary? Rovergauge is always the first solution, normally helps to narrow it down.

Everything else has been mentioned so I'm going with fuel pressure, as it only happens in 2nd and 3rd gear

[Zener]

Only when under load ? This indicates an ign issue , misfire or compont failure i.e coil, ign leads etc

[blaze_away]

Work thru stuff methodically.

1st Job: Get a smoke machine on the inlet and eliminate any/all air/vacuum leaks. Until that's confirmed you'll struggle.

Then on to everything ignition related.

[GFro93]

Thanks all. I have replaced rotor arm, HT leads, dist. cap and coil recently and am confident it is no issue with them.

I will have a look through the other suggestions methodically!

[Belle427]

GFro93 said:

Thanks all. I have replaced rotor arm, HT leads, dist. cap and coil recently and am confident it is no issue with them.

I will have a look through the other suggestions methodically!

Problem is the components you used might be worse than the ones you took off as quality is shocking these days.
List up where you purchased the coil, cap and arm from.
Don’t overlook the module either as these are a common fault, again difficult to buy as quality is not there anymore.

Edited by Belle427 on Monday 17th January 10:03

[spitfire4v8]

Belle427 said:

GFro93 said:

Thanks all. I have replaced rotor arm, HT leads, dist. cap and coil recently and am confident it is no issue with them.

I will have a look through the other suggestions methodically!

Problem is the components you used might be worse than the ones you took off as quality is shocking these days.
List up where you purchased the coil, cap and arm from.
Don’t overlook the module either as these are a common fault, again difficult to buy as quality is not there anymore.

Edited by Belle427 on Monday 17th January 10:03

Yes my advice is that unless you KNOW it's faulty, don't replace it. You will do more harm than good replacing already-fitted good components with unknown quality new ones.

[Zener]

spitfire4v8 said:

Belle427 said:

GFro93 said:

Thanks all. I have replaced rotor arm, HT leads, dist. cap and coil recently and am confident it is no issue with them.

I will have a look through the other suggestions methodically!

Problem is the components you used might be worse than the ones you took off as quality is shocking these days.
List up where you purchased the coil, cap and arm from.
Don’t overlook the module either as these are a common fault, again difficult to buy as quality is not there anymore.

Edited by Belle427 on Monday 17th January 10:03

Yes my advice is that unless you KNOW it's faulty, don't replace it. You will do more harm than good replacing already-fitted good components with unknown quality new ones.

And a 2nd opinion agree with this ^ dont dismiss faulty new parts especially after-market pattern