Idle control valve causing my problem ?

[nobananas]

Been having a touch of oddness over the last couple of weeks. As you're driving, if your cruising and then lift off the throttle the car will start to de-accelerate slowly then you get a jolt and it will slow down more rapidly. I notice that if I hold the car at around 3000 rpm (any gear) then simultaneously dip the clutch and lift off the throttle the revs will stay at 3000 (sometimes raise a little) for a few seconds the drop off rapidly which I think is the same thing I am feeling when driving. I suspected the Idle control valve so I cleaned it, no change so I replaced it with another, still seems the same. I don't think I have any leaks anywhere, have I been unlucky and just got two duff ones behaving the same way or could there be another cause ?. It settles down to idle fine and sods law I'm going on holiday Saturday and know this is going to drive me friggin nuts !

[t5 stealth]

have you checked the vac pipe on the left side of inlet manifold,
betweel power steering res and manifold,
mine split and changed the revs ,all run ok and sounded ok,just idle went strange,took a while to find it cos of where its located,cldnt see it clearly.

alternativly would be to get codes checked to see if anythin is having a moment
:) .

[si850r]

thats what mine does sometimes too mate...

[t5 stealth]

another thing that can cause odditys ,temp sender unit,
if its telling the ecu the wrong info then the engine is trying to run at a difrent setting.
ie being told wrong info.
the temp senser is one of the most important sensors as the ecu relys on that signal to know what the engine is doing,before it can tell everythin else what to do lol.

[nobananas]

have you checked the vac pipe on the left side of inlet manifold,
betweel power steering res and manifold,
mine split and changed the revs ,all run ok and sounded ok,just idle went strange,took a while to find it cos of where its located,cldnt see it clearly.

alternativly would be to get codes checked to see if anythin is having a moment
:) .

I had a good look over it last week and checked all the vac pipes etc. Found a split hose that goes to the one way valve on the charcoal canister and replaced it, found tonight that the one way valve itself is duff so replaced that thinking that would be the end of it and it was drawing off the canister but it's still the same. Had a PM off a member (thanks James) who says he's had a similar thing with two used IAC's and ended up with a new one before the problem was solved so I may have just been unlucky. I am thinking about blocking the IAC valve pipe partially with a plug with a 'tuned' hole in it. If I get the hole the right size so it passes enough air to idle at around 1000-1500 rpm it should pull the idle down quickly when the throttle is lifted but still allow the valve to control the base idle, what do peeps think ?

[si850r]

what mine is doing now mate (and this is only first start up from cold) it climbs on its own to about 4000rpm then drops slowly. The only way i can bring it down quicker is if i put it into drive then it will drop to about 900 ish..

Has the little screw moved by the throttle that pushes the arm up for tick over ( thats if u have one?)

[nobananas]

another thing that can cause odditys ,temp sender unit,
if its telling the ecu the wrong info then the engine is trying to run at a difrent setting.
ie being told wrong info.
the temp senser is one of the most important sensors as the ecu relys on that signal to know what the engine is doing,before it can tell everythin else what to do lol.

Is the temp sender just used by the ecu with a seperate one for the gauge or does the gauge read off the ecu ? Would have thought a duff temp sensor might cause starting troubles but then I suppose it could over fuel once the vehicles hot and cause weirdness !

[t5 stealth]

i suppose its possible to have 2 duff units.....thats bad luck lol.
as for doing the quick fix,i think id rather try and find the cause before i go down that root,maybe as a last resort if it was a big issue lol.
( or very expensive ) :)
as with most of these annoying probs,its a pain but usualy turns out to be somethin silly,
as you know ,these cars have a few vac pipes that make a difrence if they split/perrish etc,
i assume the vac treee thing is still intact and not leaking from pipes or any blanks on it leaking,

[nobananas]

what mine is doing now mate (and this is only first start up from cold) it climbs on its own to about 4000rpm then drops slowly. The only way i can bring it down quicker is if i put it into drive then it will drop to about 900 ish..

Has the little screw moved by the throttle that pushes the arm up for tick over ( thats if u have one?)

The screw on the throttle plate is only there to set the butterfly to prevent it 'bedding' into the throttle body so shouldn't have moved since new. Mine does rev reasonably high when started from cold but settles down fairly quickly. If I hold it at around 3 grand for a few seconds and lift off it stays at 3 grand for a few seconds before dropping, I think this is what's happening when I'm driving. It could just be a lazy IAC valve, or rather two lazy IAC valves LOL !

[si850r]

have u tried the injector o rings? thats where mine is leaking from at the mo...im just trying to source some down

[t5 stealth]

Is the temp sender just used by the ecu with a seperate one for the gauge or does the gauge read off the ecu ? Would have thought a duff temp sensor might cause starting troubles but then I suppose it could over fuel once the vehicles hot and cause weirdness !

not sure of top of my head,but most modern engines need the temp gauge to tell ecu what state the engine is in,ie hot /cold etc,thus fuelling it correctly,

i usualy do live test on diagnostics,
tell tale sign of a fault is the gauge in the car reads a difrent temp to the reading on diagnostics,
ie gauge says 80 degrees but diag says engine temp is only 35 degrees.
but as you say,there does sometimes show probs with starting etc.
diag is usualy the best way to see whats working and whats not.

[nobananas]

i suppose its possible to have 2 duff units.....thats bad luck lol.
as for doing the quick fix,i think id rather try and find the cause before i go down that root,maybe as a last resort if it was a big issue lol.
( or very expensive ) :)
as with most of these annoying probs,its a pain but usualy turns out to be somethin silly,
as you know ,these cars have a few vac pipes that make a difrence if they split/perrish etc,
i assume the vac treee thing is still intact and not leaking from pipes or any blanks on it leaking,

Everything seems okay, I pressure tested the inlet tract a couple of weeks ago and found a couple of leaks (mainly the ones way valves to the servo and the charcoal canister) and I went over all the vac pipes last weekend because I was totting up what fuel hose I needed to get to replace the silicone ones I have before re-fitting my MBC (which I haven't done yet !). Was only thinking of 'bodging' it as I won't be able to get another IAC valve before Saturday, unless that is anyone has a REALLY good one that they can get to me for Friday LOL !

[t5 stealth]

have u tried the injector o rings? thats where mine is leaking from at the mo...im just trying to source some down

are you sure its the o ring,
as inlet manifold gasket is a common fail.

[nobananas]

have u tried the injector o rings? thats where mine is leaking from at the mo...im just trying to source some down

Changed mine when I had the injectors cleaned and they were fine when pressure tested a few weeks ago.

[nobananas]

are you sure its the o ring,
as inlet manifold gasket is a common fail.

Think that may be opening an old wound with Si LOL !

[t5 stealth]

Everything seems okay, I pressure tested the inlet tract a couple of weeks ago and found a couple of leaks (mainly the ones way valves to the servo and the charcoal canister) and I went over all the vac pipes last weekend because I was totting up what fuel hose I needed to get to replace the silicone ones I have before re-fitting my MBC (which I haven't done yet !). Was only thinking of 'bodging' it as I won't be able to get another IAC valve before Saturday, unless that is anyone has a REALLY good one that they can get to me for Friday LOL !

and not forgetting the air flow meter,
but that usually makes things a bit worse than just a minor idle fault lol.

[t5 stealth]

Think that may be opening an old wound with Si LOL !

oooops
sorry si lol

[nobananas]

Well back from holiday and the old girl didn't even break down !. I ended up drilling a 6.5 mm hole in a piece of nylon that just happened to be a tight fit in the pipe to the IAC valve. This would let the engine idle at around 1.5k (trial and error with the IAC valve removed !) so still allow the IAC valve to control the final idle. Worked fine, none of the weird lift off delayed 'shunt' I was getting the only thing I had to remember (as I found out) was leave the throttle pedal alone when I start it (usually revs up to about 2.5k then dies down) otherwise it floods immediately and is a bugger to then get started ! (ask me how I know !). Will have to get a better IAC valve and remove my bodge !