Edmunds Answers

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  • karjunkie 04/29/09 8:39 pm PST

    I suspect you just have either a bad crankshaft position sensor or a carboned up idle air control valve, or possibly both after 200K miles. Each is easily and cheaply fixed so I think it is worth repairing the car. The CPS sensor is cheap and bolts to the engine with one bolt. The IAC valve is easily removed and cleaned with throttle body spray cleaner..

  • zaken1 04/29/09 8:48 pm PST

    I would recommend having the compression tested before doing any more work on the car. If the compression pressure in all cylinders is within manufacturer's specifications, and there is not more that 15psi difference between the lowest and highest readings; then the engine is mechanically sound, and can be fixed. But if the compression is out of range; then it will not be possible to eliminate the stalling. Sometimes adjusting the valve clearances will improve or even out the compression; but if that doesn't help the compression; the engine would need to either be replaced or overhauled.

  • toyotamin 05/03/09 2:52 pm PST

    karjunkie: Thanks for your suggestions. I have been using public transport and I've been too busy to try them. Will keep you posted.

    zaken1: I had asked my mechanic if he had checked the compression. His reponse was that the car wouldn't run if there were something wrong with the compression. So I didn't push him to test it. Is testing the compression a very time-consuming process?

    More information.... I have been driving my car to the bus stop which is about 5 minutes away. I've noticed that if I can keep it in neutral the idle is more stable. When I have to put it in drive, that's when the idle starts to drop and if I do not give it gas, the car stalls.

  • zaken1 05/03/09 4:48 pm PST

    Testing the compression of the 4 cylinder engine; which you obviously have (since the V-6 does not have a distributor) is a relatively simple and quick process. Your mechanic is wrong about the car not being able to run if there was a compression problem. But he may have meant that it wouldn't run if there were a massive drop in compression; such as would be caused by a slipped timing belt.

    But when an engine gets many miles on it, and the compression drops below the minimum spec; the idle stability after it warms up is the first thing to go.

  • rearwheeldrive 05/03/09 6:22 pm PST

    I like the suggestiion of electric problem, crank sensor failing when hot or ignition transitor, but I'm more on an induction problem. That is the air getting into the engine to burn the mixture

    Because you say it runs better in neutral, without load on engine,(transmission in gear), any air duct leaks or vacuum lines cracked on high mileage cars, can cause the engine to run rough. Once you start accelerating, the air volume goes way up (throttle open ) and leaks are not as noticable and compression goes up.

    Compression is always a good place to start checking on an old engine. If the air volume or compression pressures are not correct, it can cause an engine to run poorly at idle. The engine is a big air pump and it needs to be sucking air without any leaks to run right . Any leaks at idle, or an engine with low comprssion will throw the settings off. A worn timing belt will drop off your compression readings.

    Squeeze the duct going to the engine from the air filter, if it shuts off the duct its cracked somewhere.

    You say it runs better with part throttle?

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