Even if that flange was leaking slightly it would make no difference with the engine running - the EGR valve is still shut at idle and the tiny extra air ingested when the system operates would make no difference. IF the miss is in a single cylinder, rather than random missing, it's doubtful that a small/medium vacuum leak would cause that. The disconnection of an EGR vacuum hose affects the efficiency and stability of the engine. When it leaks, it can make the EGR valve not open, increase the emission of harmful gases and also cause overheating in the engine. Below are some of the performance problems that are caused by the disconnection of the EGR vacuum hose: It should be noted There may be a clogged air filter or a bad MAF sensor. Additionally, the car may have a dirty fuel filter, a bad fuel injector or a failing fuel pump. It’s also smart to check for bad spark plugs, a faulty EGR valve, a malfunctioning ignition coil or even worse, transmission issues. We evaluate these possibilities in no particular order. 1. Inspect the purge volume control valve. These are known for becoming sticky, which causes a leak. You can use your compatible scanner to open and close the purge control valve, if it won’t open or close properly, you need to replace it. The same goes for the vent control. You need to check to see if it’s leaking and causing problems. My observations: I don't have oil leaking from around my EGR. I do have oil leaking from the intercooler pipe connection and am finally taking it to the dealer today at 26,000 miles. I added my block plate at 15,700 miles and oil was already leaking from the intercooler pipe before the plate was added so I don't think the block plate caused Any fault that affects intake manifold vacuum will skew the MAF calculation on a speed density system. EGR leaks and incorrect base ignition timing frequently skew the speed density calculation of MAF. Increased EGR flow due to leaks or sticking valves will generally increase fuel and EGR flow, but decrease ignition advance. There has to be a leak somewhere for the accelerant spray to have made the engine run rough. It got in somewhere and altered fuel trim. There has to be a leak somewhere aft of the MAF or poor fueling for the system to generate a lean code. Possibilities are intake gasket, egr pipe or gasket, injector seals, or vacuum hose. A malfunctioning EGR valve can lead to a noticeable decline in engine performance. You may experience a rough idle, hesitation, or stalling when starting your vehicle. Acceleration may feel sluggish, or you may notice a lack of power when driving uphill. Increased fuel consumption. If the EGR valve is stuck open, it will allow exhaust gases to yUqtK0A.