Hey guys, hoping someone can point me in the right direction.

I have a slight misfire on idle, pretty sure it's down to a fuel leak on the spill rail, new washers are in the post. When I was diagnosing the problem, I disconnected the Egr vacuum and stuck a screw in there, also disconnected the plug. I plan on blanking the Egr and removing the cooler this weekend.

Anyway, afterword tonight I had a look under the bonnet to check the fuel pump primer and double check my vacuum pipes - I reconnected the Egr vacuum and plug, just to see how that affected the slight misfire, it made it a hell of a lot worse, I had a look at the egr valve as the engine was running and it was opening and closing in less than 1 second intervals, in tune with the now terrible misfire.

I disconnected the Egr again, sealed the vacuum and took the plug out - I was back to just a slight misfire.

The question is, why would the Egr be opened and closing like that on idle, is there a problem with my vacuum pipes and would this explain my slight misfire with the Egr disconnected?

It was opening and closing rapidly on idle, all the way open then closed, and the engine was shaking all.over the.place, has anyone experienced this before or have any idea why it would be behaving like this?

Thanks guys

Carl

Does the vacuum on the egr run on the same vac system that operates the waste gate on the turbo? I'm not as familiar with the 2.5's.
Just thinking if you have a misfire then on every fourth pop wouldn't the turbo be dropping pressure as well on that stroke causing the quick drop in back pressure and messing with the system for the actuater and the egr?? Causing it to pop open an close quickly in time with the misfire.
I might be talking complete b&llo#*s here (and someone please tell me if I am) but it was just a thought.

Thanks Mallinman,

I'm not sure but I woulod assume the egr does run on the same vac system that operates the waste gate on the turbo?

Are you thinking that the egr opening and closing is a symptom of the misfire, and not the other way round?

Once I get the air leak sorted and egr blanked I'll likely know more, however the slight misfire would explain the drop in vacuum wouldnt it?

I'm just surprised that the egr opens and closes on idle, I thought it only did that higher up the rev range..

@Cribbs1984 . Hi mate - just wondered if you ever got to the bottom of this problem? I have a slight misfire too (occasional, but very noticeable + think down on power in lower rev range) and the erratic EGR exactly as you described here. The EGR is disabled now, but the misfire is still present. Misfire starts after about 30 seconds after startups. Think it's probably a sensor/wiring failing but could do with some pointers as to where to look.

Hey buddy, this problem drove me mad. I initially thought it was vacuum pressure but that was just a symptom of the misfire. I then turned my attention to the coolant temp sensor mounted on the cylinder head.. When disconnected it wouldn't misfire - I think this is because the ecu would assume a cold engine and over fuel it. I then thought it must be an air leak in the fuel system. Turns out the fuel rail that connects the injectors needed replacing. The previous owner had attempted to bodge it with silicone (there were lots of bodge jobs I had to fix) I replaced the fuel rail and injector washers, no more misfire. Good luck with it, I hope you bypassed the egr cooler as well as blanking the valve off!

@Cribbs1984 thanks for the reply mate - been driving me made too! Had started to come to the conclusion that it must be air getting in somewhere after the pump, but no obvious fuel leaks anywhere so wasn't sure. Will get a set of washers ordered and strip it down and check out the pipework. Would rather keep the EGR in place - I know most peopple like to remove them, but it does cool the combustion temperature, so there's pros and cons to both schools of thought.

how does the egr cool the combustion chamber?

Less oxygen available, lowers combustion temps -> less NOx, but more particulates generated.