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Re: 2006 HSE RR....engine pulsates slightly when light...
1. Fuel Pump pressure too low 2. Dirty air or fuel filter 3. Plug wires running parallel for more than 6" )cross em over each other or you get crossfire) 4. Crack in Intake manifold or split end on one of your vacuum lines or vacuum cap plugs
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for an engine to backfire through the throttle body means that the inlet valve is still open when spark occurs . That means that the timing is too far advanced . IT may also mean that the tappet clearance is out if manual adjustment or the hydraulic followers are pumping up and holding the valves slightly open especially at revs.
sounds like your egr valve is opening too far at part throttle and sticking open. it is actuated by solenoids that open and let engine vacuum in. you were on a good path in checking the vacuum lines. however this may require replacing the egr valve and gasket. the egr valve is circular in shape on top and usually is bolted down with two bolts. its located on the engine side facing the firewall.
maybe the cam timing is off. If the engine was torn down and reassembled wrong, that would do it. Connect a vacuum gauge to the intake manifold and see what you get for vacuum readings.
It should be about 17 inches at idle. And, it should be steady.
NORMAL READING: Needle between 51-74 kPa (15-22 in-Hg) and holding steady.
NORMAL READING DURING RAPID ACCELERATION AND DECELERATION: When engine is rapidly accelerated (dotted needle), needle will drop to a low (not to zero) reading. When throttle is suddenly released, the needle will snap back up to a higher than normal figure.
NORMAL FOR HIGH-LIFT CAMSHAFT WITH LARGE OVERLAP: Needle will register as low as 51 kPa (15 in-Hg) but will be relatively steady. Some oscillation is normal.
WORN RINGS OR DILUTED OIL: When engine is accelerated (dotted needle), needle drops to 0 kPa (0 in-Hg). Upon deceleration, needle runs slightly above 74 kPa (22 in-Hg).
STICKING VALVES: When the needle (dotted) remains steady at a normal vacuum but occasionally flicks (sharp, fast movement) down and back about 13 kPa (4 in-Hg), one or more valves may be sticking.
BURNED OR WARPED VALVES: A regular, evenly-spaced, downscale flicking of the needle indicates one or more burned or warped valves. Insufficient hydraulic valve tappet clearance will also cause this reaction.
POOR VALVE SEATING: A small but regular downscale flicking can mean one or more valves are not seating.
WORN VALVE GUIDES: When the needle oscillates (swings back and forth) over about a 13 kPa (4 in-Hg) range at idle speed the valve guides could be worn. As engine speed increases, needle will become steady if guides are responsible.
WEAK VALVE SPRINGS: When the needle oscillation becomes more violent as engine rpm is increased, weak valve springs (6513) are indicated. The reading at idle could be relatively steady.
LATE VALVE TIMING: A steady but low reading could be caused by late valve timing.
IGNITION TIMING RETARDING: Retarded ignition timing will produce a steady but somewhat low reading.
INSUFFICIENT SPARK PLUG GAP: When spark plugs (12405) are gapped too close, a regular, small pulsation of the needle can occur.
INTAKE LEAK: A low, steady reading which can be caused by an intake manifold or throttle body gasket leak.
BLOWN HEAD GASKET: A regular drop of fair magnitude can be caused by a blown head gasket (6051) or warped cylinder head-to-cylinder block surface.
RESTRICTED EXHAUST SYSTEM: When the engine is first started and is idled, the reading may be normal but as the engine rpm is increased, the back pressure caused by a clogged muffler, kinked tailpipe or other concerns, will cause the needle to slowly drop to 0 kPa (0 in-Hg). The needle then may slowly rise. Excessive exhaust clogging will cause the needle to drop to a low point even if the engine is only idling.
When vacuum leaks are indicated, search out and correct the cause. Excess air leaking into the system will upset the fuel mixture and cause concerns such as rough idle, missing on acceleration or burned valves. If the leak exists in an accessory unit such as the power brake booster (2005), the unit will not function correctly. ALWAYS FIX VACUUM LEAKS.
change the fuel you are using. try some fuel system cleaner. this is a petty issue, every vehicle develops issues over time.a bmw owner complains about hestitations, a bmw driver enjoys the ride. DEAL WITH IT!!!
That was just a generic answer I do not know your particular car. Back in the day we put oil around the intake gaskets and if the engine speed increased or steaded we knew that we had found it. I also could be other things. Have you tried Carb/injector cleaner in with the gasoline? A vacuum leak could be too small to show on a vacuum gage but a person could look for or at least confirm a leak with the gage.
Sorry I can not be of more help.