mx5cartalk.com

So I had a noise which sounded like a belt recently, and so put in a new PS belt (no AC), and re tensioned both belts. When I was checking for recurrence of said noise (which I think has gone), I noticed a weird thing with the revs, so I made this video.

The first 30 seconds is normal idle (car is at normal operating temperature after a drive around the block), and then single pulses of the throttle. You can see that the revs come back down to 1100, and then jump around a bit before settling at idle of 900rpm. Is this normal? I've not noticed it before??

After that test the car was left to idle for 15 seconds or so, and you can see that it isn't constant idle; it moves around a bit. Again, is this normal?

The last part of the video is constant throttle pressure at a couple of rev ranges. You can see that with constant throttle the revs "pulse".

Car has stock PS, no AC, ECU, ARC intake, and exhaust, no other performance mods

Thanks in advance for any input or advice

https://www.youtube.com/watch?v=L2EFF1bUVDU

What ecu? I can't tell if your saying it's standard or not.
Around the block is unlikely to be normal temp unless you have a very large block.

Sorry, stock ecu

It was an extended drive around the block ;)

No one knows??

https://www.youtube.com/watch?v=s88r_q7oufE

If it's surging like in the following then this might help:
viewtopic.php?f=29&t=61395

Not surging like that. It is unlikely that it is ECU, being that the car has never been water logged. It is possible that it is O2 sensor being that it has not been replaced to my knowledge, and it is also possible that it is a dirty ICV which I will be taking off soon enough to clean/rebuild.

Spark plug leads?

Brand spanking new as with plugs