Hi all, Happy New Year! I'm currently hunting through possible causes of a misfire on my ABF'd Mk2. Going over everything with a fine tooth comb again I was wondering if anyone could explain the functionality of the throttle position sensor and the airbox temp sender and whether they could possibly be causes of a misfire/bad idle? Noticed today unplugging the TPS does not seem to effect engine operation from cold but once warmed up will make the revs fluctuate. Is the sensors function just to register position? (i.e if vagcom shows 0 degrees closed to 72 degrees throttle wide open all AOK?). Consistant 5v across the plug however is there a way to test the switch? With the airbox temp sender (IAT) how crucial is this to the running of the car? Unplugging/plugging the sensor has absolutely no effect on the running of the car - should there be? Any help with understanding what these sensors do and how they affect the running of an ABF appreciated. I'm probably barking up the wrong tree so thought I'd sound it out on here lol Cheers
In my experience, ABF's are really sensitive to the condition of the ignition components, especially the coil in this damp weather. ECP have a sale on the at moment so unless you have a brand new one on there I'd go and get a new BERU coilpack and stick that on. Another thing that really improved the lumpy cold idle my car always had was swapping from 3 electrode plugs to denso single electrode ones. Runs much better now. The only sensor that seems to stop an ABF running completely is the coolant temperature sender on the head.
the inlet temp sensor doesnt have much effect on engine running, you can test it by reading the values in your measuring blocks 0-70odd is fine for tps activation, mine is somewhere similar
Cheers for the info chaps. Cool, sounds like everything is all ok with both of these and I'm looking in the wrong area then. RE: coilpack I'm running a Beru mk2 coil which is brand new. Interesting with the 3 electrode vs 1 electrode plugs, might be worth looking into. I've replaced the ECU temp sender on side of head too so all good there. Noticed since changing the crank sensor the revs seem a bit cleaner now however take a while to fall back down and idles high once warm so thought perhaps the TPS might be at fault. Anyway thanks for the help
I know how infuriating these engines can be sometimes! when they work, but not 100% right. Another issue which I don't think helps is the oil seal in the distributor which wears and lets oil into the body of the dizzy. This can work its way into the cap and helps cause carbon tracking inside the cap as the oil residue burns away. Not sure if it would cause your issues but worth checking.
haha yeah you can say that again lol I've put a different dizzy on with a good oil seal to rule that one out already but thanks for the suggestion. New rotor cap too although I didn't change the rotor arm, just cleaned up the contacts. Also put on new beru leads. I think my next ports of call are the vacuum lines again (ordered some silicone ones), a proper ABF ISV again (running a mk2 digi one on there) and a new rubber ISV manifold bung. Also picked up a new ignition switch just to make sure that's all in top order for power supply. That's the entire ignition system replaced then.
idle issues could be isv related, also make sure the idle switch is clicking. you can check its functions via vagcom again as per info on this thread (get the label files while you're there too if you havent done so already!) http://www.clubgti.com/showthread.php?199583 oh and check out the pdf on throttle body adaption in my sig, theres one for setting the throttle stop position as well
Cheers John, will take a look. I have the labels already, very useful! Since the new crank sensor the issues do seem kind of air leaky/ISV related. It idles at 900-1000 until you rev where it then sits around 1500 and won't drop. I only put a Mk2 ISV on there as the old ABF one died during transplant.
cool sounds like we have made some progress at least! a mk2 kr isv is the same as an abf one, though they're going to be older so might not be worth it. how is the power now?
Good to know cheers. I'm going to say power is an improvement. It revs cleanly through the range and the weird hesitation/sticking at 2k rpm did not happen during testing after fitting the new crank sensor. I took it into the borough and it'll happily spin the wheels up however I can't get higher than second gear as it's not MOT'd and didn't want to go to far. It starts on the button every time and idles fine initially however once you rev the revs stay high and seem slow to fall. I also noticed the revs bouncing up during gear changes (clutch in). Lumpy idle and misfire still present although it does seem less violent than it was before. I had it running a good 10-15 minutes and it didn't cut out. As I say proper ABF ISV next on the list along with an ignition switch and new vac lines as well as the points you mention above. I'd like to get a proper fuel pressure test done to check the FPR - I was reading they can sometimes stick. Also tempted to try a new lambda sensor although it doesn't throw a fault code and has no effect on the car when unplugged/plugged. Search continues lol
I had a lambda sensor go, just made it drink loads of petrol and be a bit sluggish, ran fine otherwise. Apart from being about 10mpg down I wouldn't have known there was an issue just from normal driving, no misfires or anything.
Ah good to know cheers. Probably safe to rule that one out then. One other thing I possibly thought was a knock sensor at fault. I was reading that the torque setting for these is quite crucial but that seems a bit far fetched to me. New ISV on the way so will see it that helps the rev issue to get back on track.
yeah if you had them off make sure the block face is spotless and you do them up to the exact torque setting, otherwise you can bust em or they dont work right
hmm any idea what the torque setting is RJ? I think I took them off to clean the block up when it was out. Can I ask what are the symptoms of 'not working right'?
its 20nm, as for what happens when they're not working right there is a good question elsawin doesnt really give any useful input on this except to say the ecu will log a code, and check the wires for continuity. so basically id not hold your hopes up this will fix it but worth taking them off and checking the black face is spotless then retorque
spot on cheers Yeah no harm in checking, will have a look tomorrow along with the other stuff. IIRC there are two? Might be a bit of a pig to get a torque wrench on them in situe, was so much easier working on the engine when the front of the car was missing lol
yarp 1 on each side, iirc not too bad to get to, just be carefull when swinging your wrench as i managed to short my alternator + to the block when i swapped my digi, put out a nice big spark but no damage other than to my pants
I bet lol Did a bit more investigating today. Swapped all vac lines for new silicone ones, cleaned up the knock sensors although couldn't get the torque wrench in without taking alternator off etc (unplugging them made no difference so not convinced they are really contributing to the problem) and the idle switch clicks when I fully open throttle so that's all good. Put a different ignition switch and barrel on just to test, no difference here so can rule that out although I did notice the brown wire in the back on the plug was a little loose and burnt. PB ISV is definitely not helping, unplugged this once up to temp and it ran much better and idled bang on 900 rpm. The misfire is still audible but a proper ABF ISV is definitely needed so that's next on the list.
idle switch should click on and off idle, not full throttle? when you say missfire is audible, when does it occur? if you mean you can hear the idle seems to stumble every now and again so not a smooooooth burble, mine does it too! not sure exactly why it does it but it doesnt seem to effect anything
Will check switch again but IIRC it just clicks when fully open, guessing it shouldn't do that then haha. It's more than a stumble or a burble from the zaust unfortunately. It occurs on idle but you can hear it through the rev range if you progressively go up the revs, usually every 1000 rpm or so but it's most noticeable around idle and the 2krpm. It's a sort of pop, almost like a mini backfire. I'll get a video next time I'm up the garage, easier to explain without me waffling then lol New ISV arrived today so will see if that cures the idle issue.
