On a '99 Chevy Astro, I was getting multiple engine misfire code, so I installed a new distributor. That fixed the misfire, but then I got PO 340 (cam position sensor). Why would a new distributor cause this?

You may have the plug wires mis-routed so the plugs don't fire in the right order. I'd check that first. If you replaced the engine, I'd also do a compression test, see if the engine itself has a problem.

HARD TO SAY WITH OUT BEING THERE BUT THIS MIGHT HELP .
Crankshaft sensor Was the trouble with my 99 Chevy truck after replacing many components like coil cap rotor wires and so on .
http://www.obd-codes.com/p0102 Code P0300 Causes and Fixes Code p0300 is a code that is generated when your engine has a misfire that is not related to only one cylinder. Sometimes this code will be set in addition to other codes such as p0301 which means that there is a misfire on cylinder 1 (cylinder 1 is the number one cylinder when looking at the firing order. It is generally the forward most cylinder on the engine.). If these engine codes are present as well the you should diagnose those first as they are probably causing code p0300.
This code will set your check engine light and needs to be fixed as soon as possible. If it is not then you will probably need to replace your catalytic converter as well as the problem that is causing your misfire.
There are many causes for this obd code. Since it is a "random misfire" or "multiple misfire" this means that the misfire is on different cylinders and not just one all the time.
Common Causes

• Low Fuel Pressure
• Vacuum Leak
• EGR system malfunction
• Internal Engine Problems (such as low compression)

Less Common Causes

• Faulty Coil
• Faulty Spark Plugs and/or Wires
• Camshaft or Crankshaft sensors
• Ignition module
• Computer

PO 300 is multiple misfires detected
PO 301, 304, 305, 306 are misfires in cylinders 1,4,5,&6
PO 053 is HO2S Bank 1 Sensor 1 Heater Resistance
PO 106 is MAP/BARO CKT Range / Perf
PO 316 is Misfire detected 1st 1000 Revs.

On a misfire, I usually push towards the spark plugs, plug wires, and coil packs / distributor coil.
You have PO 106 and PO 053 that need to be inquired about at nearest AutoZone.
They can give you an idea as to what is the problem on these.

Did a MAP sensor **** out and cause all the misfires ?
Did a misfire cause the MAP sensor error?
You see what I'm saying ?...Something caused all the misfires...thinking MAP...but not that familiar with the function of the MAP.

Hope this helps...

did the code set for multiple/random misfire or did it set for a particular cylinder or cylinders?if it is random or multiple misfire you may want to check the fuel pressure and volume and for a vacuum leak. if it is a particular cylinder or cylinders then check your coils and also the compression to make sure the engine rebuild is good and something didn't go wrong.

Your P0303 means: "Cylinder #3 Misfire Detected." This could involve a simple matter of a bad spark plug, plug wire or something a bit more serious. If you have separate coils for each cylinder or groups of cylinders, then you need to check the coil pack to the coil over #3 Cylinder. Sometimes it could also mean a vacuum leak ANYWHERE on the Engine and lastly a Valve problem in that the intake or exhaust valve on Cylinder #3 is carboned up. I would recommend getting a Haynes Manual, available at most part stores to go through their diagnostic as to your misfire. Remember, in obtaining a Code, it has a lot more to do with a simple 'misfire detected', it's a starting point to where to look. A vacuum gauge and a compression gauge would help should it not be something so simple as a spark plug, plug wire, coil or a distributor cap & rotor button that has too much corrosion on it.

I hope this helps you a little,

As Always,

"00 Buck"

P0171------ system too lean bank#1
Po174------ system too lean bank#2
For these 2 codes, try cleaning the maf sensor (mass air flow), that is mounted in the big black hose that goes from the air filter housing to the throttle plate, if it is dirty, that will cause those 02 sensors to send a signal to the computor to lean the air fuel mixture. If cleaning it doesn't work, the sensors will probably need changing.
P0300---- Random/multiple cylinder misfire
P0316---- Cylinder misfire at start up---- first 100 revolutions.
On those 2 codes, you have to do some testing to find out why there is a misfire.
Possible causes:
dirty/malfunctioning injectors
weak coil pack
fowling spark plugs/wires
Low fuel pressure

p0300 is a random misfire. A scanner will need to tell the primary cyls that have problems. A (qualified) repair shop will need to check it. Could be from vac leaks, to fuel pressure, to spark problems????/

You have to remove the interior dog box and the distributor and coil assemblies are in the back of the engine behind the upper plenum.

i had same problem distributor gear becomes worn replace it and will most likely fix your problem they are known for distributor issues

you might have water dripping on your distributor. Need to place palstice over ac line so the water drips away from distibutor. Then by new cap, rotor and distributor.