Strange engine behaviour

[rhodri_harris]

Hi all

I've had my Griff 500 for about 2 months now (S3 before that) and I've got a weird 'feature' which I wondered if anyone could help with.

From cold (ie over night) about 50% of the time the car starts fine off the key, idles at about 1100 and pulls fine. When the gauge is between 50 and 75C the car feels 'unhappy' (not the best term I know, but not right) and pulling up to lights etc the revs drop to 400. Over about 5 seconds they will 'step' up to 900 ish. Over 75C all is fine, car idles at 900.

Now I know that I might 'see' the stepper working to boost idle but this is a bit slow, so why in this temp range? Stepper has been cleaned by Fernies and by me (twice), Air cleaner cleaned, reoiled etc as it was restricting air flow, and ECU reset.

Im not about to start changing things for the hell of it, but could this be water/fuel temp sensor thing?

One final thing is that I've been told on a couple of ocassions to slacken off the fuel cap to cure this, it did work slightly, but I just don't agree with it. It's meant to be a sealed system after all.

Cheers

Rod

[ray_von]

had a sort of same problem with my chim 500 but in reverse???.Car would start up as yours but once it hit about 70 C would only tick over at 1900rpm i was convinced it was a temp sensor fault but cleaned stepper , throttle butterfly and reset base idle all seems ok. Not same symptoms as you but you never know Hope you get it sorted

[rick.e]

My G500 has high tick over (2k'ish) when cold on damp mornings. Stop for 5 seconds at a junction and it returns to normal. Doesn't happen in warm dry weather.

[beano500]

Had similar, I think.

One problem I had was badly corroded ECU connections from the various sensors. Result Captain Kangaroo! Also, I notice a reluctance to idle sensibly when the coolant level gets low - I think airlocks get into the system and "fool" the ECU.

But then when the HT leads are at the end of their tough life, dizzy needs cleaning, plugs are shot and, of course, stepper motor wants cleaning a variety of symptoms develop....