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Old 07-29-2013, 11:28 AM
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rough idle on a chevy 502 marine

I have a 1996 Chevy 502 Marine with factory fuel injection. When I start the engine it has a idle the deteriorates as it warms up. It acts as if the plug wires are removed one at a time, as the idle gets rougher.
I have put in new R44TS plugs, a new IAC idle air control valve, but this made no difference. The timing light indicates it has about 20 degrees of advance while idling and the fuel pressure is 40 psi. It still idles rough, but runs very smooth and even at 2000 rpm.
Can anyone give me an idea as to what to try next? Bill Large

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