I have a 98 Venture with 180K on it. The past few months it has been acting up. I'm constantly getting a check engine light (cylinder 3 misfire). Changed out all the plugs. Ran great for a few days and now it's back to the same old thing... light is on. It thuds something fierce when you start it up. Highway speeds it seems fine. Coming to a stop it feels like it wants to stall - but never has. (Still reads cylinder 3 misfire by the way) Should note that it is not consistent in this problem. It can go a week running fine - the check engine light goes off and all is well. Then it's back to the thudding. Oh! And as of the last week the lights are going crazy. When I break I lose all interior lights. The turn signal (only left) makes interior lights flash and break lights go dim. Is there something that I can do to fix this or do I count my blessings that my 98 lasted me 180,000?

A flashing engine light is an indication of a cylinder misfire. You need to scan engine codes to determine which cylinder is giving you the problem. Most likely a spark plug or ignition wire issue. Possibly an injector issue. If the vehicle is high mileage it may be time for a tune up which will address this misfire issue

P0304 is engine misfire #4 cylinder Several things can cause a misfire #1 electrical which you have covered #2 Mechanical Test engine compression is should be around 150 cranking and 120 running . internal valve train components can cause bad compression and the valves then self. #3 fuel injector can be the cause suggest swapping with a know good cylinder and see if misfire follows injector.

There are a few things that can cause an engine misfire and hesitation. Does your van have a CoP ignition system? (Separate ignition coils for each spark plug) Or coil pack? You may have bad ignition coil(s); that would cause a misfire. If you have a dirty/clogged/leaky fuel injector for cylinder 3, that could also cause a misfire condition. When you replaced all the spark plugs, did you look at the plug from cylinder 3? Did they all look the same? Sometimes you can get clues to what is going on in your cylinder by how the spark plug looks: if it's white or glazed you are running too lean and could indicate fuel injection problem, if it's got burnt oil on it and it's sludgy you may have a leaky gasket or worn piston ring that is letting oil up into the combustion chamber and fouling the plug, causing a misfire. If your check engine light comes back on and it's the same misfire code, have the coil for cylinder 3 checked to see if it's weak or bad. Or you can do a home remedy check and swap a known good ignition coil from another cylinder to 3, reset the code, and see if the misfire moves to another cylinder. If it does, you know the coil is bad. You can pick up an ignition coil for pretty cheap on the internet ($30-$70) if that's the problem and they're simple to install (a pain if they're on a cylinder that's under the intake manifold, but just because you have to unbolt a bunch of stuff to get to it...time consuming but not too difficult). I have a 2001 Mazda Tribute and had a couple of ignition coils go bad, causing misfires. This seems to be a semi-common problem for early 2000's Mazdas.

You have a bad COP Ignition Coil or several

They only misfire whenever they feel like it

If you had professional software --you could road test in
Mode #06 & look at cylinder misfire counts

You need to buy a couple of coils & try in cylinder #5,
front one drivers side

If that isn't the correct one or you have several,walk the
other new coil to get to the bad ones

Disregard any other stray codes until the coil issues are
solved

If it stays on your have Class B misfire
If it flashes you have a Class A misfire that could
damage the exhaust converter

misfires are more from problem injectors, low fuel pressure or injector wiring than from plugs
have a fuel pressure test done to check for problem pressure regulator , problem fuel pump , blocked m/dirty filter
one other area of concern is the EVAP system where the purge valve doesn't vent the tank properly and causes low fuel flow rates

Misfire on cylinder #5

Plugs and wires have nothing to do
with current issue, forget the past.

Work on current misfire,control module,
cylinder coil,whatever you have.

stop by local parts store (Autozone,Advance, etc) and have them do a free fault code test. They can print out a list of faults and clear the codes

get the soft ware up grade. and have the coils checked.

there may be a software update for the powertrain control module for mis-fire monitor. check with your local dealer. but if thats not the case,these engines are known at least in my experience of having the heads crack between the valves and cause mild mis-fires. try compression testing all the cylinders and performing a leakdown test on them as well.

I would try replacing the spark plugs. The lean code can be caused by an ignition miss as the oxygen isn't used up completely in a misfiring cylinder.