91 Sub with 190K -- rough intermittent idle

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fireant - 02 Sep 2007 20:25 GMT

been chasing a miss / rough idle. Engine is smooth & strong at 1000 rpm or
higher.
So far have replaced the EGR valve, EGR controller, throttle position sensor
and air filter. Check engine light went out, idle is better but still
missing while accelerating.
So installed new plugs, cap and rotor. Plug wires have about 15K on them.
Old plugs look good, no oil fouling. Checked timing with ECS unplugged.
Exactly O degrees with 1 to 2 degrees of flutter. Advance looks normal, is
steady but went ahead and installed new timing chain set (and water pump).
Starts fine but with rough intermittent idle. Idles smoothly at 1000 rpm.
Runs good and strong at speed.

Vacuum lines? Water in gas tank? Distributor?

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zephyris - 02 Sep 2007 20:41 GMT

> been chasing a miss / rough idle. Engine is smooth & strong at 1000 rpm
> or higher.
[quoted text clipped - 8 lines]
> Starts fine but with rough intermittent idle. Idles smoothly at 1000 rpm.
> Runs good and strong at speed.

1-2 degrees of flutter at idle isn't good. Is that total or 1-2 degrees each
way? Timing chain/gears could use replacement.

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Meat Plow - 04 Sep 2007 05:34 GMT

> been chasing a miss / rough idle. Engine is smooth & strong at 1000 rpm or
> higher.
[quoted text clipped - 9 lines]
>
> Vacuum lines? Water in gas tank? Distributor?

Put it on a scope and check the timing in each cyl.

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