Hi guys, so recently I've had some head work done on an EV engine including porting, new valve guides, all cylinder head gaskets & some performance upgrades in the form of a pipercross panel filter and an autotech 270 cam. Built it all back up and the first time it started it seemed to run pretty well, however the next day when I've tried it again it immediately shot up to around 3500rpm at idle and stays there, there's also a bit of intermittent misfiring going on. I can get this down to 1900ish by turning the idle adjustment screw all the way to the right which is still a lot more than is ideal. First impressions were an air leak somewhere but the intake manifold, O-ring for the adjustment screw, rubber bellows joining onto the throttle body, and all other intake pipework seem alright, same case with the vac lines to the dizzy and the switch on the airbox. Dodgy earth was my next guess but they all seem OK too, I've also checked the AAV which is getting a solid 13.4v at idle which doesn't seem too unusual and it makes no difference whether it's blocked off or not. Is there a chance any increased airflow from the pipercross filter would throw the air mixture that out of line to cause something like this, and if so can I adjust it somehow? I'd try the original one but it went in the bin weeks ago! Any help appreciated!
Thanks for the advice, managed to get some new vac pipe today and have replaced all the ones in the engine bay I can find, checked valve timing which seems to be fine too. Got it off and had a look at the throttle body but couldn't see anything obvious, both butterfly valves seem to function well. Beginning to think it might be more to do with the ignition timing given everything else seems to be in order
Update: checked the ignition timing and found it was correct, after that I removed the throttle valve from the manifold to get a proper look at it, turns out the throttle closed switch underneath is missing the button pushed in by the butterfly valve when closed presumably resulting in the car thinking it's constantly on an open throttle. Scouting around for a replacement but I'm confident that this is the issue.
probably not the switch on its own, a few things would also have to be broken though for it to cause an issue. as on the kjet engine this sends 12v to the cold throttle enrichment valkve while throttle is open,. and cold throttle valve will only pass current if it detects hard throttle. then it sends 12v to 5th injector, and that will only spray fuel if the 5th injector thermoswitch is cold and allows a path to earth if you unplug thew switch this should disable cold throttle enrichment system, can leave it off if you like as early kjet cars didnt have this system. just have to remember not to floor the throttle hard while engine is cold, and you shouldn't really do that anyway
You weren't wrong rubjonny, managed to bodge the switch with a small piece of plastic as a temp fix but it's still made no difference. Also managed to get the idle down to something sensible by tweaking the idle CO screw and the idle adjustment on the throttle but the downside is it runs like a dog now, properly lumpy even for a cammed engine. Need to get it hooked up to a gas analyser and fiddled with ideally asap but prior to that is there a "rule of thumb" for adjusting the two? Like two turns anti clockwise from stop for the idle adjustment and 3 anti clockwise from stop for the CO or something along those lines? I'd like to get it running somewhat smoothly in order to get it to a garage!
can fine tune the co by ear to an extent, the 16v thread has a bit of info on this. also covers basic kjet checks which still apply to an 8v engine so worth a look: https://clubgti.com/forums/index.ph...air-and-tune-your-mk2-corrado-1-8-16v.195423/ for ignition timing this is done at idle with vacuum line to dizzy disconnected, use the big diamond for 6 degrees. this gets you a base figure to work from, can usually dial in a fair bit more depending on health of the engine and quality of fuel
