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'89 240SX problem

Hi All, When I start the car in the morning, it runs perfect but then starts to run rough at idle as it heats up. I'am thinking there is a bad control sensor somewhere. The computer gave me a 55 code so it thinks things are fine. When I remove a vacuum line from the throttle plate area and hear suction, the engine runs worse, so, is this telling me the engine is lean at idle? If I squirt a shot of gasoline in the vacuum line, to verify the lean condition, will it mess something up? Gas mileage is only 20 MPG. Anyone have a suggestion where to look, from a case history? Thanks, Johnboy

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Johnboy
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Check the Engine Coolant Temperature Sensor along with the Oxygen sensor & the wires leading up to them. When the engine is cold, the ECT sensor dumps more gas into the intake manifold to heat the engine / exhaust manifold gasses faster so the catalytic converter can do it's job of filtering the exhaust air. It the Engine Control Unit thinks the engine is still cold after the engine has warmed up, it will continue to dump more fuel into the intake causing the rough idle. Procedures on how to test the Engine Coolant Temp Sensor & the Oxygen sensor can be found on the Frequently Asked Question webpage at

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Anyhow, hope this helps... ID '95 240 SX SE

.....August 27th, 28th & 29th, 2004....Las Vegas Nevada.....

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Johnboy wrote:

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Idlafie

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