986 Boxster Intermittent Idle Issues
Discussion
My 986 Boxster has some idling issues. I've had a few people look at it but no-one seems to know what's wrong.
When the car is warm and stationary (e.g. at traffic lights), occasionally the revs will just drop to zero and the car needs to be restarted. It doesn't happen all the time and there doesn't seem to be a specific set of conditions that will trigger it.
Other times when it's stationary the revs will repeatedly 'blip' of their own accord (not by a huge amount but you do end up looking like a bit of a twit revving your engine at people at traffic lights).
I've read that a lot of idling issues are in cars with air con however mine doesn't have this option
It's also had the MAF (?) sensor changed recently so this isn't the cause.
Does anyone have any suggestions for how to fix this problem?
When the car is warm and stationary (e.g. at traffic lights), occasionally the revs will just drop to zero and the car needs to be restarted. It doesn't happen all the time and there doesn't seem to be a specific set of conditions that will trigger it.
Other times when it's stationary the revs will repeatedly 'blip' of their own accord (not by a huge amount but you do end up looking like a bit of a twit revving your engine at people at traffic lights).
I've read that a lot of idling issues are in cars with air con however mine doesn't have this option
It's also had the MAF (?) sensor changed recently so this isn't the cause.Does anyone have any suggestions for how to fix this problem?
+1 Goose
The Throttle valve can clog / coke up around the idle point (closed throttle), this means when the throttle closes on over-run that it can get jammed shut - erratic idle can also occur because the dirt will not allow the throttle to move correctly to its idle position (it cyclically opens and closes the throttle trying to get to its final position).
The above problem can be a symptom of a previously faulty MAF (system runs too rich, causing carbon in the intake, replacing MAF sorts the richness but the carbon stays, hence the secondary complaint).
Removing the intake and cleaning it with careful use of carb cleaner and a rag is a quick and cheap fix.
Intake leaks can cause a similar set of complaints, things like the AOS (Air/Oil separator) and its connections to the intake/cylinder head can allow unmetered air into the intake depending on relative engine movements (over-run forces twist the engine the other way on the engine mounts compared to accelerative forces for example and can open a split pipe that at all other times is closed - they're the tricky ones to find
)
The Throttle valve can clog / coke up around the idle point (closed throttle), this means when the throttle closes on over-run that it can get jammed shut - erratic idle can also occur because the dirt will not allow the throttle to move correctly to its idle position (it cyclically opens and closes the throttle trying to get to its final position).
The above problem can be a symptom of a previously faulty MAF (system runs too rich, causing carbon in the intake, replacing MAF sorts the richness but the carbon stays, hence the secondary complaint).
Removing the intake and cleaning it with careful use of carb cleaner and a rag is a quick and cheap fix.
Intake leaks can cause a similar set of complaints, things like the AOS (Air/Oil separator) and its connections to the intake/cylinder head can allow unmetered air into the intake depending on relative engine movements (over-run forces twist the engine the other way on the engine mounts compared to accelerative forces for example and can open a split pipe that at all other times is closed - they're the tricky ones to find
)Pope said:
+1 Goose
The Throttle valve can clog / coke up around the idle point (closed throttle), this means when the throttle closes on over-run that it can get jammed shut - erratic idle can also occur because the dirt will not allow the throttle to move correctly to its idle position (it cyclically opens and closes the throttle trying to get to its final position).
The above problem can be a symptom of a previously faulty MAF (system runs too rich, causing carbon in the intake, replacing MAF sorts the richness but the carbon stays, hence the secondary complaint).
Thanks everyone. I suspected it might have been a sensor or something similar so I'll get the OH to give the throttle valve cleaning a go for me The Throttle valve can clog / coke up around the idle point (closed throttle), this means when the throttle closes on over-run that it can get jammed shut - erratic idle can also occur because the dirt will not allow the throttle to move correctly to its idle position (it cyclically opens and closes the throttle trying to get to its final position).
The above problem can be a symptom of a previously faulty MAF (system runs too rich, causing carbon in the intake, replacing MAF sorts the richness but the carbon stays, hence the secondary complaint).
Pope said:
+1 Goose
The Throttle valve can clog / coke up around the idle point (closed throttle), this means when the throttle closes on over-run that it can get jammed shut - erratic idle can also occur because the dirt will not allow the throttle to move correctly to its idle position (it cyclically opens and closes the throttle trying to get to its final position).
It gets jammed closed, where have you seen this ? As when you first turn the ignition on the throttle body carries out a spring test to snap it closed to make sure in an emergency it can snap it closed. The fault is gumming/varnishing of the throttle body and your air gap reduces causing a very poor idle... have you ever tried to hold a throttle butterfly whilst it is in operation..... It would break your fingers off The Throttle valve can clog / coke up around the idle point (closed throttle), this means when the throttle closes on over-run that it can get jammed shut - erratic idle can also occur because the dirt will not allow the throttle to move correctly to its idle position (it cyclically opens and closes the throttle trying to get to its final position).
You can check the throttle plate angle on idle with PIWIS tester and if it is more than so many degrees (think its 6 or 9) then it is not in its idle position as its being held off the stop by the gumming of the throttle body. You then clean the throttle housing and butterfly with a cleaning agent and that should do the trick.Mike
sportsandclassic said:
It gets jammed closed, where have you seen this ?
At work........... Had one a few weeks ago that literally needed prying open when I checked it - maybe it's the dirty air down south??!! (e-gas, 986S Tip, London based) Diesel Cayenne suffers a bit with it too - modified SW in DME stops the valve closing now to combat the issue - the joys of emission control systems and carbonised intakes.
If you have an early engine ie before the electronic throttle you should look at the idle control valve. These valves consist of a rotating cylinder in a bore with a fairly fine tolerance. Over time the cylinder corrodes and when it gets to the point where it starts to bind on the housing you will get poor control of idling and revs. Being a techie I stripped mine down as far as it can go and cleaned it off, re assembled it got quite a bit more life out of it. Need go check if your car has this valve.....
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