Bone Idle

 I've mentioned that I'd messed with the Stylus' throttle cable with somewhat mixed results, the new cable route was technically better, but the idle was unstable, swinging from 500 to 1,200. I took the car out & while it was drivable, it wasn't pleasant, the engine took a long time to drop to idle, giving the unnerving feeling that I was speeding up, because I wasn't slowing down as fast as I'd expected. It was also popping & banging like a bastard.

I'd re-designed the pulley block for the cable & printed it in ABS for strength, but this gave problems, the first bit of travel passed across the pulley, rather than away from it, so didn't pull the cable much at all.

Yes the new version is orange - what of it? It's actually orange because that ABS filament seems to print much nicer than any other colour I have.

I decided that part of the problem was the stiffness of the cable going round the pulley - really I should've used a 2" pulley & may well re-design it again now I know I have space. I swapped the bike brake cable for a bike gear cable (hands up who knew they were different) & that worked better, but the idle was still poor. I wondered if the throttle needed some help to fully close, so I found some small tension springs I'd squirreled away years ago & fitted one of those. Again it was better, but not right.

Next I decided that while running the new cable route & forcing my arms into gaps too small for them, I might've disturbed the throttle bodies & caused an air leak. I took off the entire inlet system & found that yes, one of the vacuum tubes feeding the MAP sensor wasn't as far on as I'd like. They didn't seem very tight, so I shall get some fuel hose to replace them in case the modern petrol is slowly eating them, for now I tyraped them on. I took a few things apart & had a good look round - my home designed & printed intake trumpets are standing up well to the heat & vibration - then carefully re-installed everything.

I started the engine & not only did it not idle, it went straight to the red line! Eeek! I shut it down very quickly & re-checked everything, it all looked good, nothing forgotten or hanging off. I released all the clips sealing the throttle bodies to the intakes & this time lined them all up with much more care. With fingers crossed I pushed the starter button & it ran with the same lumpy idle. For some reason I started looking at the slow running screw, a couple of degrees made the difference between lumpy & 600 RPM & smoothish at 1,200 RPM. But when I backed it off further so it wasn't touching the throttle lever at all - smooth as you like & 750RPM. It's NEVER idled smoothly at 750 RPM. I think the slow running screw being set was stopping the ECU just controlling the idle, there's also no occasional "sneezing" (it made a noise I can only write as "TSHA" every 15 seconds or so) & while it's a bit of a worry when stone cold, idling at only 500, once warm it's nicer to drive than it's ever been.

My fingers are firmly crossed as it RogueRunners Devon III this coming weekend.

On a separate subject I received an e-mail today from the Blackbushe Air Day - just an advertising mail shot really, but in the description of the classic car section was this from last year's show:-

There we are look, fifth from the front & almost out of shot.