Car runs good at higher rpm... when idling one piston doesn't fire.. all spark plugs have been checked produce spark... injector has been replace on problem cylinder..my next step will be to check compression... hasn't been done yet.. exhaust manifold was cracked but has been welded shut.
Start car, un-plug one spark plug wire at a time and you should hear and see a spark. that means that one is working fine, then go to the next if you dont see a spark from that one after unplugging then that one needs a coil.
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Just for fun, I'd do a compression check on #1.
If it is low, at low RPM it would explain the misfire.
At higher RPM the compression happens faster so the source of the does not have as much time to allow pressure drop, so the mis-fire disappears like magic.
Reply as a COMMENT to this post to let me know what you find.
Very likely a low fuel pressure problem. Have you changed the fuel filter? Check the fuel pressure against vehicle spec's while running at idle and again at about 3000 RPM. Also check pressure with key on/engine off. If you lose pressure between idle and higher RPM's you probably have a weak fuel pump. Same goes for if you lose pressure after initial key on/engine off. You could also have a problem with a weak ignition coil, spark plug wires or spark plugs but not as likely.
REPLACE SPARK WIRES THAT COULD BE MISFIRE PROBLEM, ANY TIME OLD SPARK PLUG WIRES IS REMOVED THE WIRES WILL BREAK INSIDE PLUG BOOT CAUSING SPARK PLUG NOT TO FIRE.REPLACE SPARK PLUG WIRES.CLEAN FUEL INJECTORS, CHANGE AIR FILTER,CHECK ALL VACUUM HOSES ON THE INTAKE MANIFOLD LOOKING FOR INTAKE VACUUM LEAKS.
your probably feeling a rough idle of the engine. need a tune up?
in park the engine is not loaded down, just idling at a low rpm=rough
in drive with brake on you have put some load on motor also at low rpm=rough
in drive on the road engine is at higher rpm, = smoother
generally 4 cylinder motors idle a bit rough, especially if one spark plug is not firing right or fouled or one bad spark plug wire. tune up may fix it. if it is not stumbling real bad or stalling then you can live with it.
I had a power problem, when cold idled just fine,when warm it would miss at idle, spudder on acceleration and sound just fine at higher rpm. found number three spark plug wire had burned through lower boot. Spark was firing to head at low idle. same wire burn twice with about 40000 mile between.