98coppermetallic

I have a 98 K1500 5.7 vortec. I just purchased a jasper re-manufactured engine in January and with the engine I put new plus, wires, cap, rotor, cam sensor, tps, crank sensor, fuel filter, air filter and gear on dist bottom and the truck has been good. I now am getting a rough idle and a P0300 code. I had my mechanic run diagnostics on the truck. He said my timing is off when it idles. When you give it a little gas it corrects the timing. He's thinking I may need a new distrib or a ECM. He has a good used dist he wants to put on and try and if not he was thinking ECM. I was wondering if that sounds correct to you guys. I was thinking my fuel pump was lose pressure but didn't know if it would cause the time to be off. Any help would be great.

RacerX

why doesnt he just move the distributor to fix the timing retard? you cant set timing at idle, you have to be a like 800rpms in neutral. Loosen the hold down bolt and move the distributor back and forth slowly to hear the perfect tune if you dont have a timing light. You should be at -10BTDC I believe for this motor. Someone will confirm this.