Engine shakes when at a Stop

I have a 1991 Astro Van the van is shaking when I come to a stop. I just tune it up and installed a new IAC Valve and it still does it, but I noticed my oil gauge going increasing pressure at a stop nag coming back to normal
when I drive. Is there anyway of finding out if the oil pump is causing the rough idle at a stop.
Thanks Mike
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The oil pump is not causeing the rough idle. The low idle speed is causing the eratic and low oil pressure. Was it rough before your 'tune-up'? Maybe you knocked a vacuum line off or something else or you could have had a vacuum leak before the tune-up if it ran rough then. You could check or have your diagnostic codes checked (Free at Auto Zone I hear.) and see if it points to something. Don't spend money on parts until you have a clear diagnosis.
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Did you replace dist cap and wires?

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I replaced the cap and I replaced the wires 2 Years ago, but tonight I took the wires off at the dist cap and the one wire started arcing to the other one so I put one off the old wires back on

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My old 88 4x4 S-10 Blazer with a 4.3 V6 has a horrible idle. I still see it, as the current owner is a buddy. Most of it is caused by a cracked plastic vaccume line he refuses to replace, a clogged up TBI unit, and dirty injectors.
The TBI's can get pretty gunked up in the PCV port, and the other vaccume ports. Plastic vaccume lines are bad for cracking and breaking apart, and dirty injectors are often more evident at idle. Charles
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