Club G40 Forum
Technical => Engine and Transmission => Topic started by: dub-disaster on October 13, 2011, 06:35:38 pm
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My engine will returns to idle normally until around 2-1.5k where it hesitates for a second like you've blipped the throttle it will then return to idle slower than usual.
Second symptom is sometimes it will rev up to 2k on it's own and stay there regardless of if I rev the engine over 2k it will just keep settling to 2k after a couple of minutes it will settle down on it's own.
Final symptom is when returning to idle usual idle is a constant 950rpm but occasionally it will hunt up and down between 1-1.5k, if the throttle is partially open whilst this is happening it still does the same, it will continue to do the same if I rev it and let it settle again it will settle on it's own after a few minutes.
Could this be a vacuum leak ? Or a poor sealing throttle body. I have checked both of these and the 51mm body I've got seals as well as an oem one (not perfectly but good enough) wouldn't think this would be to much of a problem as the idle screw let's air past anyway.
Checked the vac system over and replaced all pipes so can't see it being this either. Also of there's a vac leak surly the map sensor would read any pressure changes and adjust accordingly ?? Can't see any strange fluctuations in vac reading on guages.
Any ideas or pointers ??
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Very common problem with 51mm throttle bodies.
Jezza's car does it, but if you snap off the throttle from a wide throttle opening it's fine - presumably because the butterfly is snapping shut with enough force to seat and seal pretty well. If you ease off the throttle gently though, it seems to stick a little bit, creating exactly the symptoms you describe.
The hunting revs is Digifant trying to do its best to stabilise the idle - it does this by swinging the ignition timing around. Obviously this only works up to a point, and if the throttle plate is stuck slightly open it'll be fighting a loosing battle. You can't send air down a wire!
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Cheers for that Andy I'll grab another throttle body and see if it cures it.
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Ok tried new throttle body today and it actualy made it worse !! Had both bodies side by side and the seal is identical both operate fine on and of the car to be honest the 51mm one is slightly better.
Still having hesitation returning to idle and this erratic up and down hunting could this be caused by anything other than a leak vacuum side of the throttle plate? could it be the ecu maybe ? Any other areas to look in.
I've checked over and over again for vac leaks and all is good. Can hear a slight hissing from around the top plastic boost pipe I'm assuming this is just air traveling through it I did take it of and there are no cracks and it is air tight checked all connections above and below boost pipe. Still can't solve this problem.
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We should compare bays mate. Swap bits over and see if it sorts anything out. You using the standard bendy boost pipe?
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how about trying to put a stiff spring for when you release the pedal, if full close the tb..
just an idea!
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Is the ignition timing set 100%? And idle speed adjusted okay?
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Just to check if its ECU in panic, does the same happen if you pull the water sensor off? Just check see If there's no change with it off or on. Just something I found once because there wasn't an ECU light on my 1st one (I not sure now if this one has either)
Neal
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right, ignition timing is set on the z mark, it does flick around a little but 80% of the time bang on the z marker, the idle is set to 950rpm and it does idle at that apart from when its hunting around. it only hesitates for a second or so at 1,5k then will fall to 950rpm some of the time and other times it will hunt up and down.
the ecu seems to be "happy" as it will go into service mode no problem with the blue temp sender unplugged. when in service mode i checked but didnt adjust the timing as it was ok, i wound the idle screw up and down and the idle did change reset that to 950rpm again then replugged the blue sender before switching of.
yes im using the standard plastic top boost pipe. jezza drop me a pm n let met know when your about see if we can worksomthing out over the weekedn ??
could the ignition alone rev the car up to 2k and hold it there for a few seconds or cause these problems or should i still be looking for leaks in the inlet system somwhere??
with the standard throttle body on it reved up to 2k and stayed there immediatly stoped the engine and took the top part of the body of and the butterfly was shut tight.im assumimng it would have to be a pretty large leak for it to rev to 2k and stay there ??
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I'm sure its the ECU, can you check the idle sensor and wide open sensor lines? Ones not stuck (w/o) or not working is it?. Bet you've done a quick avotest check they change.
Cool mate
NEAL
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Idle switch is working fine can hear it click and when driving i can see the fuel cut when I close the throttle on my afr guage wot switch is a 6psi boost switch now. These would surly cause fueling problems anyway and the fueling is all fine as it should be.
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you sure the battery and alternator are pumping out good voltage? sometimes revving etc can be down to sensors cutting in and out with rubbish voltage (so i'm led to beleive)
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you sure the battery and alternator are pumping out good voltage? sometimes revving etc can be down to sensors cutting in and out with rubbish voltage (so i'm led to beleive)
Both alternator and battery are brand new and putting out good voltages
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with the standard throttle body on it reved up to 2k and stayed there immediatly stoped the engine and took the top part of the body of and the butterfly was shut tight.im assumimng it would have to be a pretty large leak for it to rev to 2k and stay there??
Did you adjust the idle screw on the standard TB to set it up?
Are you using Polo CL pulleys and timing markers?
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What about a new ISV?
Not around this weekend mate. Got monday off if your around?
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has anyone managed to solve this problem??
mine has exactly the same symptoms and its driving me crazy as its my daily!
could it be the springs in the throttle body a bit knackerd and not snapping the butterfly shut properly
im looking into the 51mm body to try and sort it...
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I thought mine was caused by pipes from the vacuum and fuel system getting stuck behind the arm on the throttle body . This fixed it temporarily then it cam back. Havnt driven the car and tried to sort it though the things I did and it didn't help included.
Using a completely standard throttle body - this ruled out any sealing issues as my 51mm seals better than the standard!!
Replaced all earths including run ing a separate on for lamda sensor.
Adjusted all linkages and stops for correct function of throttle - this didn't help
Watched the throttle through a mirror on the bonnet closed fine no problem !
Replaced all vacuum system with new silicone hose
Checked for vac leaks using a butane gas torch
Checked ignition time twice with different timing lights
Havnt tried chaining ecu and chip although this was going to be next on list
New coil didn't help
New leads and plugs didn't help
Checked for boost leaks no help
New lamda didn't fix it
You can try all those things although I'm convinced that hunting revs and slow return to idle is a vac leak issue I'm just thick or not experienced enough to find it !!
One more thing is Jezza once had a problem like this and was caused by the routing of his breather pipe when he removed the breather completely it stopped, I was going to try that next Aswell.
This is a realy common problem with g40 and one there seems to be no easy/definitive answear for unfortunately.
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thanks alot for reply, which breather pipe do you mean?
ill give that a go and see what happens
also its a long shot but are you running a cone filter or the airbox? might put my standard airbox back on and see if theres any difference
ive checked for boost leaks a thousand times! changed the blue temp sensor, played around with the throttle body cleaned it greased the springs etc, but none of this has helped
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Hows your ISV? Might be worth giving that a serious de-gunking. One more thing there is a throttle stop on the throttle body, its on the left of the unit at the front, its a screw and a nut. try having a play with that.
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thanks for that ill have a play about today
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My pipes were all moved and it has stopped it. I get occasionally the high rev but thats cause i need to sort out the stop bolt... still.
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ok which pipes/breather pipe do you mean? and do i move or re-move to cure it?
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There is only one breather pipe on the back of the block.
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I know this is an old thread but i finally (fingers crossed) have sorted this ruff/lumpy idle hunting.
I took the top t-piece off to use some liquid metal on this small hole on the wall and with the engine running there was a very loud suction whistle sound coming from the idle hole. It sounded too loud imo so I covered it. The rpm dropped and the engine ran a lot better.
Squirted a nice amount of WD40 into it and then adjusted the idle screw till it was lower as the revs were slightly high. Were just over 1000rpm now around 900rpm.
Took it for a drive and so far its been spot on. Even round town where it usually happens, its stopped.
Not sure if it was the idle thats stopped it or the adjusting if the screw.
Anyway if anyone has similar problems, this is always a good route to take.
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T peice?
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t-piece on top of throttle body
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ah right cheers