| Originally posted by PR325is+Apr 6 2005, 12:24 PM--><div class='quotetop'>QUOTE(PR325is @ Apr 6 2005, 12:24 PM)</div><div class='quotemain'><!--QuoteBegin-Cruzin 323is@Apr 4 2005, 04:32 PM |
mass air flow sensor might need to be changed... some sympotoms of this is the dip in rpm, then the car shuts off because not enough air is getting to the engine! the check engine light should be on!
how much would the replacement cost??
Ive been going trough with the rpm dipping.
here is what ive found.
Bad Mass airflow sensor, can cause this. Replacement is the only best solution.
Dirty idle control valve, can also cause this. on M50 engine the valve sits underneath the intake manifold, making it a great place for oil to deposit into it, since it sits lower that bottom of manifold.
Dirty, or damaged, engine airvent hose. THere is a hose that goes form the top front part of the valve cover back into the intake manifold, on the rubber boot before the trottle. this hose is a vent, is creates vaccumm on the inside of the engine to prevent the oil from going past the seals, with time, oil vapor condenses on this pipe and clogges the pipes, but since its oil, sometimes air can go trought, and so the engine revs fine,, sometimes the oil accumulates to a lower spot on the pipe and so no air goes trough, and so the engine goes wako., Ive pulled this out of my engine and it had enought oil in there to clogg it up depending on how the car was sitting, very tricky.
Engine temperature sensor, (remenber there are two, one for dash, one for DME) this sensor tells DME when to decrease fuel enrichment, needed on cold startups.
Air temperature sensor, on intake manifold, this together with the mass airflow meter lets the DME to presicely calculate air density being taken, this way it can calculate amount of fuel to be injected.
Fuel pressure regulator, mounted on fuel rail, it regulates fuel pressure by regulating the return flow of gas, controlled by a vaccum tube attached to intake manifold. Normally the regulator can get stuck or clogged. Vacuum pipe, made of rubber, desistegrates with time, loosing its tighness.
Failing fuel pump, if fuel pump is about to fail, it wont be able to sustain pressure on a continuous basis, meaning a constant fuel pressure.
Evaporative Gas Recopery purge valve, this valve is mounted outside the carbon canister, is purpose is to inject gasoline fumes stored on the carbon canister into the intake manifold during startup, helping on startup and also burning off gasoline vapors, instead of letting them go to the atmosphere. If purge valve is stuck open, it will keep injecting extra fuel fumes on manifold when the car is runing, creating a rich burn and therefore upsetting iddling speed.
For fuel delivery problems, its recomended to use a fuel pressure gauge tap into the pressurized fuel line, this way you can, using the proper manual, identify fuel delivery issues. If nothing shows up, then go for the engine sensor and eletronics, this also includes looking for loose wires, corroded grounds or plugs and dirty connections. Remember, most sensors give of voltage as inputs, this voltage changes based on resistance that changes within the sensor, if wiring is faulty, resistance within the wire will give off bad readings to DME, therefore the DME cannot calculate whats going on..
After replacing almost all of this things on my car and checking to make sure they all work, there is one little thing that causes engine Rpm dipps.
Faulty fuel injector, the injector does not open totally, or closes, causing lean, rich, situation, making combustion uneven and therefore unstable. The reason a faulty injector does not show up much on high rpms, is because the injector is beign activated more times than on idling, so it does not show as much..
You can try using those injector cleaners, but most of the time it wont help much.
Look on internet to buy new, or remanufactured injectors.
So for i havent totally keept this anoying thing from happening, but it did improve a lot, so le tus know.
Rule of thum, this cars are getting ye old, so is no wonder this things happen, since wiring gets dirty, corroded, loose, and rubber hoses and components crack and fail. So it comes to a point that replacing all this is necessary, it hurts a little on the wallet, but aint a biggie.
let us know how it goes.