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Doug B

Automobile engine revs up and down during parked idling -- what causes

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Got a 2003 Ford Taurus SES, 6-cylinder, automatic transmission. There are three symptoms that are vexing me:

1) When idling, the engine will rev up and down all by itself, fluctuating between 600 and 1400 rpms or so. The effect is exactly like someone gently pressing down on the gas pedal and then letting up, over and over. This effect is most notable when the car is parked, but also occurs when stopped for red lights, or even during low-speed driving (under 35 mph or so).

2) The car struggles to go up bridges in the usual Drive "gear" now ... you really have to gun it or shift to D1 (?) to get the rpms up. Before, you could just gradually increase the gas while in the ordinary Drive "gear" and going up bridges was a piece of cake.

3) In concert with the above, the Check Engine light has been for about 6 months :wub:, and it ain't the gas cap. I have avoided getting the code read because last time I had that done, it cost $100. My understanding is that I can buy a code-reader for myself for much less than that ... but I have put off buying the code-reader :rant:. It is also said that I can go to Auto Zone and Pep Boys and get the code read on the spot for free ... but I have also put that off (I am not a car's best friend, I guess :hot: ).

The symptoms described in #1 have been on and off for since July ... when the Check Engine light first came on in May, nothing was apparently wrong. I originally blamed the problems on bad gasoline, and STP Gas Treatment (Engine Treatment?) improved the situation markedly for a few weeks, but the symptoms have since returned.

Anyone else ever seen this? I'm sure it's happened to others.

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Got a 2003 Ford Taurus SES, 6-cylinder, automatic transmission. There are three symptoms that are vexing me:1) When idling, the engine will rev up and down all by itself, fluctuating between 600 and 1400 rpms or so. The effect is exactly like someone gently pressing down on the gas pedal and then letting up, over and over. This effect is most notable when the car is parked, but also occurs when stopped for red lights, or even during low-speed driving (under 35 mph or so).2) The car struggles to go up bridges in the usual Drive "gear" now ... you really have to gun it or shift to D1 (?) to get the rpms up. Before, you could just gradually increase the gas while in the ordinary Drive "gear" and going up bridges was a piece of cake.3) In concert with the above, the Check Engine light has been for about 6 months :thumbdown:, and it ain't the gas cap. I have avoided getting the code read because last time I had that done, it cost $100. My understanding is that I can buy a code-reader for myself for much less than that ... but I have put off buying the code-reader :wall:. It is also said that I can go to Auto Zone and Pep Boys and get the code read on the spot for free ... but I have also put that off (I am not a car's best friend, I guess :wall: ).The symptoms described in #1 have been on and off for since July ... when the Check Engine light first came on in May, nothing was apparently wrong. I originally blamed the problems on bad gasoline, and STP Gas Treatment (Engine Treatment?) improved the situation markedly for a few weeks, but the symptoms have since returned. Anyone else ever seen this? I'm sure it's happened to others.

I have a 2000 Taurus that was doing this for a while (#1). My dad knows everything about cars so I took it in to him and got it fixed. I'll call him later and get back to you....

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I have a 2000 Taurus that was doing this for a while (#1). My dad knows everything about cars so I took it in to him and got it fixed. I'll call him later and get back to you....

:thumbup:Gracias.

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The surging and lack of power sounds like a vacuum leak or more likely a bad MAF (Mass Airflow Sensor). That would throw a CEL (Check Engine Light) as well.

Edited to expand acronyms...

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Got a 2003 Ford Taurus SES, 6-cylinder, automatic transmission. There are three symptoms that are vexing me:1) When idling, the engine will rev up and down all by itself, fluctuating between 600 and 1400 rpms or so. The effect is exactly like someone gently pressing down on the gas pedal and then letting up, over and over. This effect is most notable when the car is parked, but also occurs when stopped for red lights, or even during low-speed driving (under 35 mph or so).2) The car struggles to go up bridges in the usual Drive "gear" now ... you really have to gun it or shift to D1 (?) to get the rpms up. Before, you could just gradually increase the gas while in the ordinary Drive "gear" and going up bridges was a piece of cake.3) In concert with the above, the Check Engine light has been for about 6 months :thumbup:, and it ain't the gas cap. I have avoided getting the code read because last time I had that done, it cost $100. My understanding is that I can buy a code-reader for myself for much less than that ... but I have put off buying the code-reader :confused:. It is also said that I can go to Auto Zone and Pep Boys and get the code read on the spot for free ... but I have also put that off (I am not a car's best friend, I guess :rolleyes: ).The symptoms described in #1 have been on and off for since July ... when the Check Engine light first came on in May, nothing was apparently wrong. I originally blamed the problems on bad gasoline, and STP Gas Treatment (Engine Treatment?) improved the situation markedly for a few weeks, but the symptoms have since returned. Anyone else ever seen this? I'm sure it's happened to others.

Plugs or ignition coil would be the first things I'd look at. Take the car to a local auto parts chain store, they will likely be able to tell you the code for free. Similar thing happened on my '02 Concorde and at 140,000 miles the original plugs were hosed and one of the coils was shorting out. Cost about 70 bucks to fix, but it runs like its new again.

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The surging and lack of power sounds like a vacuum leak or more likely a bad MAF (Mass Airflow Sensor). That would throw a CEL (Check Engine Light) as well.

Forgot about this one as well. The guy that helped me when my CEL came on thought the same thing at first, but the meter told us what was really wrong. Best to get a free check!

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1) When idling, the engine will rev up and down all by itself, fluctuating between 600 and 1400 rpms or so. The effect is exactly like someone gently pressing down on the gas pedal and then letting up, over and over. This effect is most notable when the car is parked, but also occurs when stopped for red lights, or even during low-speed driving (under 35 mph or so).

Had a 93 accord do same.

Solve for the honda was cleaning the Idle Air Control Valve (IAVC). It was about the size of a candy bar and right up on top of the engine. Easy fix.

removed with 2 or 3 bolts, one elec. connection and sprayed it down with carb cleaner. There was also a small wire screen filter that needed cleaning, carb cleaner'd it also.

Fixed.

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These Tauruses are noted for having horrible transmissions. I had an '01 Taurus, and had a similar problem where the car was having problems downshifting from 2nd to 1st, so that when I slowed down and would get back into the gas, it would rev and not catch. It was a problem with a sensor in the tranny, and they were going to have to basically take the powertrain apart to get to the sensor to check/replace it. Wasn't worth it, got rid of the car. My mom had a '96 Taurus that required a full tranny rebuild after hand grenading going up the side of a mountain.

Your first item does sound like a vacuum/MAF/Fuel injection problem of some sort, but the second sounds like a transmission issue. If this thing has more than 75k miles or so, make your time.

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I had a similar problem with my ride. It ended up being some sort of wiring issue with the cruise control.

You can get your codes checked for free at Autozone and Checker auto parts.

Pep Boys charges a diagnostic fee.

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