Discussion
Oh Great Gods of Nob, I bow to your combined superior knowledge and pray that you can solve my technical problem. Having changed the plugs in my 2.5 and solved the 'missing' at high revs by re gapping them to about 1.5mm, I now have a new problem. All was well for a week or two when suddenly the car has decided to almost stall when I come to a roundabout or junction. It doesn't happen every time, but when it does, it comes so close to stalling the oil light comes on and even the fan stops. A small blip on the throttle brings it all back to normal until the next stop. Tick over is around 600 revs when things are ok.
It's all a little disconcerting, as I'm worried that one day I will slow onto a roundabout and then give it a bootful to find the engine has stalled and I'm left in the middle of the road!
Your great wisdom is appreciated.
It's all a little disconcerting, as I'm worried that one day I will slow onto a roundabout and then give it a bootful to find the engine has stalled and I'm left in the middle of the road!
Your great wisdom is appreciated.
. It should be more like 1 mm or less.Your idle speed seems kind of low - was it 600 rpm before you changed the plugs? Is your A/C and/or headlights on? I usually set the 3 liter motors in our cars to ~850 rpm.
I'd probably start by double checking the spark plug leads to make sure that one hasn't popped off, or is making an intermittent connection. If you can, check to see if all the plugs are firing.
Second, I'd suspect a vacuum leak. In neutral, bring the engine up to about 3000 rpm, hold it there for a few seconds, then pop off the accelerator pedal. If the engine speed dips way below the idle speed, like 300+ rpm, then most likely you have a vacuum leak of some sort. Check all of your vacuum lines to make sure one isn't loose or deteriorated. I usually zip-tie all vacuum line connections, so they don't blow off with boost. You can use ether, brake cleaner, carb cleaner, or propane to search for leaks - with the engine running, spray a little on each likely place (hose connections, the junction between the upper and lower intake manifolds, the boost gauge pipe, etc.) and see if there's a change in the idle speed. Or, even better, use (or have a shop use) a smoke machine to check for leaks.
The third thing to check is the idle speed screw - if it's loose, can be turned in and out by hand, and doesn't have a locknut, chances are it backed out a little. Add a locknut, readjust, and see if that fixes your problem.
I'd probably start by double checking the spark plug leads to make sure that one hasn't popped off, or is making an intermittent connection. If you can, check to see if all the plugs are firing.
Second, I'd suspect a vacuum leak. In neutral, bring the engine up to about 3000 rpm, hold it there for a few seconds, then pop off the accelerator pedal. If the engine speed dips way below the idle speed, like 300+ rpm, then most likely you have a vacuum leak of some sort. Check all of your vacuum lines to make sure one isn't loose or deteriorated. I usually zip-tie all vacuum line connections, so they don't blow off with boost. You can use ether, brake cleaner, carb cleaner, or propane to search for leaks - with the engine running, spray a little on each likely place (hose connections, the junction between the upper and lower intake manifolds, the boost gauge pipe, etc.) and see if there's a change in the idle speed. Or, even better, use (or have a shop use) a smoke machine to check for leaks.
The third thing to check is the idle speed screw - if it's loose, can be turned in and out by hand, and doesn't have a locknut, chances are it backed out a little. Add a locknut, readjust, and see if that fixes your problem.
I haven't had any time to fiddle with the car yet, but I do know the idle screw has a lock nut and isn't loose. I've held the throttle at around 3000 revs and come off it, it didn't stall, but then it doesn't happen every time anyway. I did wonder if it sounded a little lumpy when holding the revs though.
Also, I don't know if it's my imagination but...the nearside(uk)appears to be 'whooshing' a bit louder than normal and not necessarily from the usual area? This might be me going slightly mad, but you do tend to 'tune in' to these cars and notice minute differences.
Oh, it only happens when the car has well and truly heated up.
Does this help suggest what the problem is?
Also, I don't know if it's my imagination but...the nearside(uk)appears to be 'whooshing' a bit louder than normal and not necessarily from the usual area? This might be me going slightly mad, but you do tend to 'tune in' to these cars and notice minute differences.
Oh, it only happens when the car has well and truly heated up.
Does this help suggest what the problem is?
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