Hi all, i have a mk2 GTI with a 2E conversion. It does have a slight issue. When you lift off the throttle, the revs stick at about 1200 and then takle about 30 seconds to drop all the way down to 900. Then when the car is idling the revs will sometimes shoot back to 1200 and start the process again. I cleaned the ISV out which hasn't helped. Any ideas where to look next? Throttle switch? Cheers
are you using the mk2 manbagment? if so, the throttle should snap shut to the stop firmly. if not, check the throttle cable adjustment. if its not that it could be the idle switch is adjusted too far in. if that checks out make sure you can hear the idle swithc click just as the throttle shuts fully. if not, adjust it. bit tricky as its underneath the tb. also, check the wiring to the throttle switches, it likes to snap behind the throttle body.
Cheers fella. It has mk3 management and loom. There's only one switch on the TB and that's on the bulkhead side of the butterfly rather than underneath. I don't hear a click when the throttle shuts. How do you adjust the switch?
Oh yeah, today i cleaned the butterfly and degunked the breather pipe. Now the car seems to want to idle at 1000rpm. It still takes about 30 seconds to settle though. When i disconnect the temp sender, it idles at about 1400. Is that normal?
Cheers fella. I didn't do the conversion. The seller told me the 2e came from a rado but it may well be mk3. Not sure if that would make a difference. It's Digi2 management and the loom seems to have been replaced too. There's only one switch on the TB, which is on the bulkhead side of the butterfly rather than underneath. I don't hear a click when the throttle shuts, how do you adjust it? Today, i cleaned the TB and removed some gunk from the breather. Now it seems to want to idle at just over 1000. It still takes 30 seconds to settle though. If i disconnect the temp sender and rev the car, it then wants to idle at about 1400. Is that normal?
Soz for the multipost. Am not used to posts being moderated before they appear and thought they'd just got lost in cyberspace
My old Mk3 did this for a while and drove me up the wall, i swapped and changed so many parts. It just stopped one day after i clarted everything i could see with WD40. Has me puzzled to this day that one.
ah ok, what you have on the throttle body is a throttle position sensor rather than an idle switch, with this just pop the inlet boot off and make sure the throttle is nice & clean inside, and there are no missing or damaged vacuum hoses or pipes. the rubber bung for the rocker cover breather valve is prone to splitting, so worth popping that off to have a look. ISV could be dead, if you can find another in the scrappy I'd try that. a MK2 8v one will also work if you can find one
Cheers. The airbox has been ditched in place of a cone filter and consequently there aren't the vac lines going to the temp sensor that the car should have. I had a good look but haven't been able to see where or how they would have been connected. I wonder if that may be involved. Perhaps it's losing vaccum?? The idle does go to pot when i disconnect the ISV so i'm assuming it's working. Haven't managed to get the breather off the valve cover, i undid the 2 screws off the plastic cover and that's as far as i got. I didn't want to tug it too hard and knacker it. The confusing thing for me is that it settles down to idle and then randomly shoots up to 1200 again. I don't really see how a vac/air leak would cause that behaviour.. Edit. I've just had a thought. Is the throttle position sensor in any way related to giving the ECU a signal for the MFA MPG? I ask because i have the 99.9 readout problem and the rest of the MFA works fine. If it were involved then that might imply the sensor or wiring might be duff. Just a thought.
as long as there are no open vac pipes causing a leak its all good! once the screws are undone the breather should pop out, if you run the engine and let it idle try wiggling it without pulling the valve off to see if the idle changes
Braved the snow and had a good wiggle of the valve breather and all associated pipework today with no affect on the idle. I'm starting to suspect the sensor. I've noticed that when you release the throttle, the revs do actually drop to where they should for a split second and then instantly rise up to 1200. I think i might get a new TB gasket and pull it off to have a good look at the TB.
Pulled up at the farm today (-9 degrees!!!) and the idle stuck at 1400 and stayed there. Popped the hood, blipped the throttle, forcibly returned it to the idle position and the revs went back to 1200 and then did the 30 second drop thing. It seems likely that it could well be a cable or adjustment issue afterall.
Scratch that. I've tried blipping the throttle with the cable detached this morning and it made no difference. I've given the TB and throttle spindle another good going over with carb cleaner again and no joy there either. Would a dicky coolant temp sensor possibly cause this? Or am i just clutching at straws now? Today when i disconnected the sensor, it made absolutely no difference to the problem. So far all i've acheived is to introduce it occasionally revving up to 1400 and sticking there. Got me stumped this one.
Not sure if this is relevant with the mk3 management but I've had similar idle problems on my 8valve mk2 - idles high, drops a bit then goes back up. Turned out that the ignition timing was advanced too far. Mind you, the car was quite jerky to drive as well but it might be worth checking.
was that a K-jet or digi mk2 eddiet? I unplugged the vac pipe from the top of the TB and as i expected, it raised the idle. So to rule out a leak from the pipe i replaced it. Then, as i've done some fettling, i disconnected the battery for an hour to try and make the ECU go to default settings. After reconnection i let the car warm up without touching the throttle until the fan kicked in and went for a drive. Including some full throttle bits. Result, no change. I did find this rather interesting bit in another thread on here; Originally Posted by VeeDub_RS I need to adjust the idle on my Mk3 2 litre. Its a K reg so think its a 2E ? It could be a 2E, have a look at the sticker in the service book. Quote: I've checked the haines but cant seem to find it in there ? The ISV is disconnected when i connect the plug the revs charge up to 3K so i think somewhere along the line its been adjusted to get the revs down. You can't find it because you can't adjust it (directly!) When the car is running under power, then the throttle position is being measured by the potentiometer (TPS) on the back of the throttle butterfly. When you take your foot off the pedal, the throttle butterfly snaps closed. To stop the car stalling at this point, there is a bypass system (set by the screw on the side of the throttle body). This allows a small amount of air to leak past the butterfly to stop the car stalling. As the throttle butterfly closes, the engine control unit (ECU) notices the change in reading from the throttle positon sensor (TPS) and starts up the idle control program. It then adjusts the ISV to keep the revs at 900rpm. If the ISV is broken, or the idle bypass screw is set wrong then too much air will get into the engine and the revs will rise. So it is one of the following things: 1. Too much air leaking into engine. Caused by: Broken ISV (not very common) Idle bypass screw set wrong O-ring failed on idle bypass screw Air leak in engine breather system Missing dipstick plastic sleeve Gunk around the throttle butterfly. Other random air leak. 2. ECU doesn't know it's supposed to be idling Caused by: Broken wiring to TPS (very very common) TPS adjusted wrongly / broken. My money is on broken TPS wiring, and the idle bypass screw has been adjusted wierdly to stop the engine stalling. Remember the idle bypass screw is only there for that fraction of a second when you take your foot off the pedal to stop it stalling. That idle bypass screw seems relevant at first glance. Any thoughts?
Not sure if this will help but I am currently running with a faulty ISV which is causing a similar problem, even when it is unplugged it seems to be letting air through and holding the revs up. A quick test you could try is to squeeze the hose coming from the ISV to the inlet manifold, while the engine is running. This will show you if the problem lies with the ISV or if the ISV is open. Hope this helps
It's a digi. Not sure about the idle screw but I wouldn't have thought the revs would drop to the right level at all if it was set too high.
Cheers malt, i'll nip out and give it a go. Though if i unplug mine the idle does get real lumpy and it buzzes on step 2 as it should. eddiet, i may be reading it wrong but it doesn't look like it's an idle screw as such, seems the ECU sets the idle. In the flesh though, it does look exactly like an idle adjustment screw I was thinking more along the lines of the bit about the o ring and adjustment issue. As if more air than needs be is getting by and fooling the ECU into thinking it's got a tiny bit of throttle input. or something. I was expecting you to say yours is a k-jet. So would i be right in saying that if the default timing is too far advanced the ECU can't compensate effectively? Anyone in Devon got an ISV i could borrow for ten minutes ?
That seems to be the case for mine. I had a fast, lumpy idle and quite a jerky ride at low revs. As I haven't got a working timing light I just turned the dizzy clockwise while the engine was running and it's idling now nice and smooth at 900rpm. It still needs to be set properly but doing it like that seems to have worked as a temporary solution. If you're going to do that I'd mark the original position of the dizzy so that you can put it back if moving it doesn't cure the problem
