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Weird thing!

Timbo2

Timbo2

New member
Just got home after my normal 20 mile commute, stopped to open the gate and noticed the idle speed was going up and down by about 100rpm, in sinc with this was a whirring or hissing sound which came and went with a corresponding change in rpm, car running fine other wise. Left it for about 20mins restarted all normal! Anybody any ideas?
 
I have had this happen too. Still not sure of the cause but I noticed a whining noise coming from near the fuel filler cap and wondered if the seal/vent on it was faulty? No effect on running/performance as far as I know and seems to happen randomly.
 

ORIGINAL: Timbo2

Just got home after my normal 20 mile commute, stopped to open the gate and noticed the idle speed was going up and down by about 100rpm............Anybody any ideas?
Click to expand...
Get some electric gates fitted. [:)]

Sounds like it might be an air leak of some sort.
 
Sounds like it might be an air leak of some sort.
Click to expand...

Richard, electric gates would be nice but any thoughts on an air leak that fluctuates with the rpm, or that goes away after its left for a while?
 
OK up date, well it hasn't gone away, drove to work this morning, stopped after about 10 miles, no problem, by the time I got into work 20 miles doing it again, and again when I drove home to night, left it for 10 mins started her up and idle was normal.
The idle fluctuates at about 1 second intervals in time with a sound rather like an air valve opening and closing. When I pulled the dip stick out a little way it would smooth out for a while. Odd thing is it seems temperature related. Any further thoughts anyone. Richard, before you say anything, I'm not moving 10 miles nearer to my work!
 
Timbo, if it is being caused by the air bleed valve being switched then it could well be caused by the operating relay ( presuming it is done in the same way as the 944's which often had this problem ) thinking back the relay which caused it was referred to as the DMU? Not totally sure on the title of it but changing it fixed the problem in most cases of hunting and I have no idea if it is still done this way or where it may be fitted!

Not much help but it may put your search in the correct direction.[8|]
 
Thanks guys, I'm now kinda thinking it sounds like excessive vacuum so maybe its got something to do with the AOS, the thing that puzzles me is that if I go and start it now from cold it will be fine, it only does this when its fully warmed up say 20miles or so, then if I leave it for 10mins it would start up fine.
 
Saw the same sysmptoms on one of my members 996. Tightened down the oil filler cap properly and problem resolved. You never know, worth checking.
 
Does it sound as though its hunting? I had an issue a couple of months ago with up and down revs plus a hissing squirting noise. The cure for me was to clean the throttle body out it transpired that the butterfly was jamming open slightly. Thorough clean and all is well.
 
Mine was intermittent to begin with then it became constant after a couple of weeks. I had no loss of performance whilst I had the issue.
 
Might look into that next week, can it be done insitu, or what's it like to remove? could that be temperature related?
 
I too would go with the throttle body needing a claen.
Over the years gum builds up inside the housing around the throttle butterfly, this gum comes from the oil mist fed into the induction and this is normal operation.
The gummy deposits stick the butterfly to the throttle body.
The idle speed is controlled by the throttle motor (this opens the throttle in relation to the accelerator pedal position), When you take your foot off the accelerator completely the butterfly closes completely - as the engins revs decline to idle speed the motor slightly opens the butterfly to maintain tickover, with gummy deposits the butterfly sticks so more power is applied to the motor which then as the stickness frees - opens the throttle too wide so in reaction to the rising revs it closes the butterfly again - hence the hunting as the process repeats.

A good clean should sort this out
 
OK,so the other day I was driving home stuck in traffic and the idle was going up and down, after a while it stopped and returned to normal! got home and everything seemed normal. Decided to clean the throttle body anyway, it wasn't that dirty. So start up, all normal, go for drive seemed normal, get home and it began fluctuating again but not so regularly and eventually settled down. Probably need a long run to fully check this out. Before when it was doing its fluctuating thing if I took off the oil cap it threw a wobbly, now when its running normally and I do this it keeps running normally! Any one any further ideas. AOS?
 
Timbo2, the throttle body and butterfly area need to be spotlessly clean - the butterfly fits like a door does in its jamb, the gum deposits here, however, if you are satisfied this is good and clean perhaps a throttle readaption could help.
disconnect battery - reconnect, turn on ignition but dont start, leave like this for one minute for the throttle position adaption process to complete, switch off, then start up
 
No need to disconnect the battery on a 2.7. Note the other parameters:

F50015C01F914E1BA3464CB6E1D32FC4.jpg
 
So I have done the adaption thing. Throttle body spotless. I still have a problem but doesn't seem as bad as before ( remember it sort of cured itself before I did any of this), now it seems intermittent, all is well until the car just about reaches running temp, then we have uneven idle, not like before which was a regular rise and fall, but still with the sound of someone blowing down a pipe, or a valve opening and closing. Give it a few blips on the throttle and it settles down, left it running until it got thoroughly warm, no issues. Definitely temp related.
Other odd thing, my RMS leak seems to have stopped! (there is still oil in the car!).
 
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