Fast idle on startup function

[Album56 0]

Hi guys , my G60 has a wandering hot idle any where between 850-1000rpm after 18yrs of rock steady 850rpm, have checked all the usual suspects, all vacuum pipes are fine, blue temp sensor changed, ISV is clean & working ok, CO pot appears ok, idle screw & seal is new, idle microswitch operates & tests ok, loom tested for continuity from engine sensors/switches to ECU plug ok, all earths cleaned/tightened. ECU removed & inspected, nothing obviously wrong, multi-pin plug looks clean, sprayed with contact cleaner anyway, lamda probe recently renewed with geniune Bosch one, lamda earth wire good & tight. The car is completely stock & now I'm wondering if the fast idle on startup function is intermittently cutting in because it wanders to 1000rpm but no higher? If I slow the idle down to 850rpm by letting the clutch start to bite in gear it will quite often then stay at 850rpm until I blip the throttle again.

The 2 suspects I have left are ECU or dizzy faulty, I take it the fast idle on startup is a function of the ECU, Ive got my hands on a good second hand one now & will be fitting that next week to see what happens....

Corrados heh, never a dull moment :D

[Album56 0]

Tried setting the base idle again today, got her nice & hot pulled the cam cover breather pipe off & pulled the plug off the blue temp sensor, the idle increases to approx 1100rpm, the strange thing is the idle screw has no effect on idle speed that I can detect whatsoever until it comes out & then air whistles in & idle increases to 1250rpm, over the whole range of its travel it doesnt change the idle from 1100rpm so I just unscrewed it a turn or so from fully in & left it there.

Checked the CO pot which was set at 403 ohms before I tried adjusting it & found that did affect idle speed when adjusted by many turns but not by much. Ended up setting it back to 403 ohms & when the plug was put back on the blue temp sensor the idle falls back to approx 900rpm but as soon as I blip the throttle to 3000rpm 3 times .to clear the memory it idles back at 1000rpm each time. The throttle cable is fine & not sticking.

The strange thing is when started from cold it behaves perfectly for the warm up cycle & after idling at 1000rpm for a short while then falls back to 850rpm until temperatures start to rise & then it will start to rise again to 1000rpm.

I am determined to track this down, took the plugs out the other day after a good run & they looked slightly rich to me, black but not sooty but not nice brown colour either.

Trying the other ECU tomorrow, will update this thread.

[Supercharged 2]

If the idle increases when the BTS is unplugged then something is not right - I would check the ignition timing first as this procedure should be done before the CO.

 

Could be something simple like an air (vac) leak.

[Album56 0]

Well tried the other ECU today & if anything it made matters worse, was idling at around 1200rpm when warm after set-up, tried switch off engine & disconnect ISV plug & then re-start & that improved things to around 1000rpm hot idle. Put the original ECU back & back to square one. Now thinking I need to get timing checked & make sure the dizzy etc is working correctly, strange that this started to happen shortly after I had new plugs/dizzy cap & rotor.

I was told at the time that several different Bosch distributors were fitted to the G60 & mine is a "type 4". Does anybody know if new ones are still available from the dealers or Bosch & roughly how much it is?

Found a thread on the Canadian corrado club forum from a guy who had a similar problem, read thro it quickly & he changed alot of stuff & checked everything but there didnt seem to be one thing that he did that definitely cleared the problem it just went away as mysteriously as it appeared on his car??

I'll read it again more carefully in a minute to see if there are clues.

Mick

[Album56 0]

Closing in on a problem now, there is no 12v heater supply to the lamda with the ignition on, looks like that old favourite the lamda loom to the plug by the engine mount again. Has been repaired years ago by the dealers when it failed MOT on emissions then the signal wire & the earth next to it were pieced out & repaired. Cant see any obvious breaks but the 12v on pin1 is missing & pin3 has no earth.

If I am correct pin1 red/white is +12v, pins 2 & 3 should be earths & pin4 the signal wire to ECU.

[Album56 0]

The red/white apparently comes from the fuse panel & uses same fuse as the fuel pump which is working ok so not the fuse blown. Its stand on yer head time with the door sill cutting into your back peering up at a mass of wires/plugs behind the panel to see if I can see that red/white wire to check for 12v that end. The loom in the engine bay disapears down by the fuel pipes & servo vacuum pipe but there is a bit of slack after I unclipped it from the bulkhead, cant see where it goes but can get my hand down there & feel it going into the corner & it seems quite loose at least thro the 1st skin, can also hear what sounds like a connector moving about inside. Need assistance now, someone to tug gently on the loom while I look up at the wires behind the fuse panel.

If I cant find it then I'll just have to find a suitable ignition switched 12v to use & run a new wire.

One things for sure it wont have done my fairly new lamda probe much good & what about the old catlytic converter...

[Album56 0]

Apparently the heater supply for the lambda on a G60 doesnt come on until the engine is running so that turned out to be another non-fault. This fast idle when hot is an electrical/electronic problem I'm sure because it varies up & down in small steps sometimes like something is breaking down or a bad connection. I have checked all the loom connections which are all good, throttle switches are good, earths are good, the distributor still has the plastic cover over the fixing bolt so the timing is still as set at factory. The main suspects left are the dizzy, apparently the ECU uses small variations in timing along with mixture variation by the idle valve to achieve a steady 850rpm. The ISV is clean & working.

What I am not sure about is how the timing is varied, is it a mechanical function within the dizzy, ie. the hall sensor moving or is it electronic within the ECU?

I still think its tied up with the fast idle on start-up function, is this part of the Eprom function.

These are quite technical questions I know but I have a basic knowledge of electronics & I'm determined to find the problem.

Cheers Mick

[Album56 0]

Next stage new air temp sender/co pot part no 037 906 040B £79, arriving tomorrow at dealers, I'll initially set it to 500ohms across pins 1 & 3. Original one has gone faulty after I wound it up & down, it now goes dis at the higher resistance setting so its set on 180 ohms at moment.

Could have been the co pot all along causing the idle to wander I guess, naa that'd be too much to hope for. If the new CO pot doesnt fix it then the ECU is coming out again, I may try swoping chips with the one from the spare ECU.

[Album56 0]

Well have a nice shiny new CO pot set at 500ohms, made no difference, car still runs perfectly except for this cursed wandering idle when hot, starting from cold its fine & behaves perfectly even settles down to a nice 850rpm idle for a short time until things start to warm up after 5mins or so from cold & then idle starts to wander up & down between 850 & 1000rpm . Have read that the hall sensor in the dizzy can become temperature sensitive when they get old & tired, this is my next suspect. A hall sensor type dizzy is very basic, just a 3w sensor with a revolving metal disc with 4 windows & a permanent magnet. The only bits that move are the metal disc with windows & the rotor, but the sensor itself does become tired apparently & if it doesnt fail altogther it can cause wandering idle symptoms when hot.

Has anybody managed to replace the hall sensor? they look quite simple to replace if it wasnt for the metal disc with windows which is in the way. Any advice would be gratefully recieved.

Mick

[dannyboy 0]

you cant change the hall sender really,its more of a change the whole dizzy job.there is a way to test it with a led but cant remember off the top of my head. the hall sensor is just a trigger mechanicanism for the coil to fire.doesnt have anything to do with idle or timing directly,thats more down to the postion of the dizzy.

 

did you remember to cancel the hot idle function by slowly revving the engine upto 3000 rpm 3 times?

[exturbo2003 0]

just a thought but you remove breather and then bts and then rev 3 times over 3000 and allow to idle, set idle speed and then switch off, reconnect bts and breather and restart. but you never mentioned turning off before reconnecting

as for hall sensor dont bother yes you can change it but its a pain as bits are a interferance fit and hence very tight so would recommend a new dizzy every time

[Album56 0]

Cheers guys, new dizzy then. Its a real pity the hall sensor cant be changed easily because some Bosch ones are available for around £30-40 as opposed to the cost of a new dizzy which I imagine is gonna be around the £200 mark plus then having to re-time everything. Does anybody know the VW & Bosch part Nos for a G60 dizzy? I was told by the dealers that 4 different ones were fitted to the G60 & mine is a type 4 which presumably means the latest one when I got a new cap & rotor.

Mick

[Album56 0]

Quote:-

just a thought but you remove breather and then bts and then rev 3 times over 3000 and allow to idle, set idle speed and then switch off, reconnect bts and breather and restart. but you never mentioned turning off before reconnecting.

 

Yes you are right, is switching off important? My trouble is that I cant get the idle to 850rpm with the BTS disconnected, as soon as I disconnect the BTS with the engine hot idle rises to 1100rpm & the idle screw makes hardly any difference over the whole of its travel which could mean false air is getting in but I have checked all the vacuum pipes & devices connected to the manifold & all are good. maybe inlet manifold gasket or injector seals but there are no noises whistles/hisses or sucking air noises & it runs fine on the road.

Mick

[dannyboy 0]

wont bother turning engine off,doesnt do anything.except save fuel.lol

 

the engine revs should drop not rise when you take the BTS off.

it does sound like you got a massive vac leak somewhere or...

you didnt take the ISV plug off while engine was running didnt you? it screws the drivers in the ECU and will never idle right again

[Album56 0]

I have been careful not to disconnect the ISV with engine running or ignition on as I read it can damage the ECU & the ISV seems to work ok. Wish I had timing light maybe I'll purchase one, I'm pretty sure the timing is wandering because when I monitor the boost pressure on the display its 530 ish at idle while idle is 850rpm which is about right for a stock car but when idle starts to rise to 1000rpm the boost pressure falls to 470ish which can idicate timing too advanced.

Trouble is I'm not sure wether this fall in boost pressure indicates the cause or wether its just the result of the engine running slightly faster...

[Album56 0]

The more I think about it the more I'm convinced its an electronic fault as it wanders up & down while I watch it without touching anything. If it was a vacuum leak idle would be constantly high which its not. And its something thats affected by temperature, my moneys on the tired old hall sensor still. If I had a Bosch part no for the dizzy I'll check with dealers & GSF price of new dizzy if they're still available...

[Album56 0]

The dizzy is quoted as Bosch 0237520044 on GSF webpage, apparently used on many of the older 1.8 VWs, also listed as £96 + VAT = £113, not as expensive as I feared. Dont know what the dealers price is but I imagine it will be more.

Trip to GSF next week not too far away in Poole.