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I've had my car in and out of the shop for several weeks and I'm really becoming very frustrated. I don't really know ANYTHING about cars, but about a month ago the car would sporadically have trouble maintaining gas flow (The RPM would teeter around 1 and then go down to 0 and shut off).

The first mechanic said that they fixed the problem by replacing the battery leads (that cost $90). The next day the car stalled on a main road and I was able to get it to a national brand car shop. They diagnosed the problem as needing a new fuel injector and pump (the diagnosis was $125) and they estimated the problem would be well over $900 to fix.

So I got the car home and debating my options (that is a lot of money to put into a fairly old car with lots of miles). I ended up taking the car back to the first mechanic and told him what the second mechanic said was wrong. He couldn't find this problem with his computer tests, but did end up replacing the fuel injector and pump (for $700).

I've had the car back for a few days now and I am STILL having struggles with starting the car and it occasionally stopping while driving (like it isn't getting gas). I am really so frustrated and upset that the problem is still acting up, especially after all the money I have spent (almost $1,000).

I would have just sold the car off instead of fixing it if I had known it was going to cause this many problems. Can anyone tell me what they think could be going on and causing the car to still stall and not start properly? I am going crazy. I don't really know the first thing about cars, but I just feel so frustrated by the problem not being fixed with all the money spent.

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Well, now they are saying they will replace the "mass flow sensor." It will be another 230$. Thank you all for the feedback, but at this point I just regret getting any repairs done. I should have just sold the car for scraps and put that money I used on a repair toward a new vehicle. I just feel so defeated and unsure, but I will let you all know if replacing the mass flow sensor fixes the issue. FINGERS CROSSED! –  Sarah Apr 15 at 20:33

3 Answers 3

It is difficult to pinpoint the exact reason for your idling issues without further information or knowledge of your Mercury Sable.

However, a common cause for idling/stalling is a perished/broken/cracked/disconnected vacuum line that results in a vacuum leak. Vacuum lines are essential in maintaining engine idle.

The fix would involve identifying any disconnected/perished lines and connecting/replacing them as need be. If you know where the vacuum lines are, a rudimentary test to check for vacuum leaks involves spraying carb cleaner around the vacuum lines. If you notice a change in engine RPM, this indicates the presence of a vacuum leak.

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I plan on taking the vehicle back in tomorrow as I had a lot of trouble with it stopping on me this morning on the way to work. I will introduce your idea of the vacuum leak. I literally know zero about cars and how they work, so most of this terminology I don't understand. Thank you for your answer, Zaid, and if anyone else has any feedback it is also appreciated! –  Sarah Apr 10 at 15:29
    
@Sarah : I hope you find a mechanic who doesn't play parts roulette. As you've learned the hard way, it can be quite an expensive game! –  Zaid Apr 10 at 18:06

Update: April 17th

Zaid, thank you for all your responses. I'm sorry if I am not correctly using "comments" or "answers." I am going to offer the vacuum leak as an idea to the mechanic. They ordered the mass flow sensor but it didn't fix it so luckily I wont be charged for that. Unfortunately, they said they "just don't know what's wrong with it." They have a professor of mechanics at a local tech school coming in to take a look at it. It is very discouraging news, because over 1,000$ and more than 3 weeks later and I still don't have a working car. I just have to sit and wait.

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It could be a few things.

I am not buying the vacuum leak idea, as engines that have vacuum leaks normally run terribly, as they are running too lean.

However, you said that they replaced the fuel injectors, so assuming you didnt get hosed, they are fine.

The first thing is a fuel filter. If one of these gets plugged, it wont run at all, but bits of debris can plug it intermittently. Im surprised they havent replaced this as a first step. I would have done it before the injectors. If you can't get the car to die by flooring the throttle, it would be my guess that this is the problem.

The next problem could be the fuel pump, if the system isnt being pressurized, the injectors cant accomodate for the load, and the engine will die. You can test this by flooring the gas pedal. If the engine dies, it is a pump problem (assuming injectors are new)

The worst case is a dead computer. If the computer isnt working right, they are expensive to replace. You might be able to score one off a crashed/scrap car, but I wouldnt really trust it.

Before you worry about replacing the computer, or anything else, think about cleaning the Mass Airflow Sensor, as an incorrect reading here might be causing fuel supply problems, if if it isnt throwing a code. This isnt hard, you mostly just unplug the unit and spray it with a can of cleaner. If you search for an engine diagram on your car, it will show it.

Engines only need 3 things to work: Spark, Air, Fuel. Too little of any of the 3, and the car wont run.

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The fuel pump has already been replaced. I doubt that a dead ECU would exhibit what is clearly a "mechanical" issue. Your reasoning for excluding the vacuum leak as a possibility is actually consistent with the OP's symptoms. –  Zaid Apr 11 at 7:41

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