i have and 87 iroc with a 350 in it..heres my problem the car idles just fine but when you put a load on it it randomly missfires and when it does the whole motor jerks but its not constant..just put plugs in it and it has fairly new wires..any ideas what could b causing it?

 

Lots of stuff. You should probably replace your cap and rotor if you haven't already to eliminate them as a possibility. After that I would look at fuel pressure under load. If it is low then the problem is likely your fuel filter or pump.

 

just put brandnew cap and rotor on it too..so im kinda at a loss.

 

Like I said, it could be lots of stuff. Low fuel pressure under load would be my next guess but it is possible that the problem exists at idle as well but is not as noticeable. Also, check your timing if you haven't yet.

 

What brought this problem on?

 

Low fuel pressure shouldn't cause a misfire under load, just a lack of power.

Since you said you recently put plugs and wires in the engine, the first thing I'd check is the firing order of the plugs wires. It's very common to get #5 and #7 mixed up. The engine will idle fine but misfire when driving.

 

I had the same problem for 2 yrs, new cap, rotor, pickup coil, wires, plugs. Replaced all those twice and still had a misfire, replaced the distributor with a new msd one and new msd wires and ran like a new car again.

 

well i had recently put a new cam in it too..its not a huge cam but i still have the stock ecm

 

I went through a parts replacement roulette hell for a year with this stuff and different things would affect it but nothing cured it until I got my third ignition module... Replaced wires, coils, caps, rotors, modules, some more than once. I had 2 modules fail on me, both Accel (had an accel coil for the second one), replaced the second with an Ac Delco module, and it cured it.

I also had a jumpy tach problem. you could see the tach jumping erratically at idle. And I never noticed it for a while but you could actually barely hear the engine skip when the tach would jump. Different parts combinations would make for misfires at 5k RPMs or above 2.5k RPMs.... some under WOT only, some under 1/2 throttle or more. It was just weird and I still dont know exactly what cured it, but I think it was finally getting a decent module in there.

I dont know why I had to go through so many parts, but modules are cheap, give it a shot. make sure you use the heat conducting gel/paste whatever under it though.