Your engine problems are unrelated to the relay.
Did you replace the plugs, wires, cap and rotor button with new quality parts, dont go cheap here and use the factory plugs. These are high performance engines, if you go cheap youll join the P0300 groud, muitple ramdon misfires and swear the problem isnt those parts becuase you just replaced them.

Low idle problems only when cold could be your IAC isnt working. The IAC controls low speed ilde when cold.

As for the relay, unplug it and see what happens. Both of the relays you show in teh pic should be the same, swap the wiring and see what happens. Personally for the $8 each I would just replce them and never worry about it again.

 

Replace them for sure. We sell them at autozone for $13.

 

I'm a techhead not a gearhead so I'd have to go pull the receipt and see what exactly I bought. I know price isn't everything but I did not buy the cheapest items on the list. I went middle of the road as far as price goes on the cap, rotor button wires and plugs (I know it was a platinum plug). There is a night and day difference to it running after warming up.

I was going to replace the coolant temp sensor but if you think it sound more like the idle air control, I'll go there first.

Is there anyway to test it? Or just have to replace it and see?

 

its a device which holds in scents that attract zombies! they are on there way to get you run!!!!!

 

Ok... checked and the relay on the right is the fuel pump relay apparently. I disconnected the plug from it and the engine just turned over, no attempt to run.

I bought a new one at Advance for $9.99. No difference in the way it runs but at least it's one more thing I don't have to worry about.

It got dark on me (started late) so I did not have time to see what the relay on the left was for or to see if it was the A/C, fyi.

I replaced the air temperature sensor (I believe that's what it's called), that's inside the housing/duct after the air filter. No difference on how the engine runs.

I don't know if it's came back or I just been too sidetracked to notice, but I had time for a leisurely drive this evening and I have a miss after the engine warms up. So it still runs a little rough/has a slight miss the same whether it's cool or warm.

Again, it's not bad but it doesn't have the power that this engine should have. It's ok on take off but not a lot of passing power. When sitting still idling you can feel the rough idle pretty noticeable.

I deliver mail in this truck part time so all I do all day when I'm driving it is stop and go so that's why I guess I didn't notice the miss after it warmed up cause the engine is just constantly revving up and down from mail box to mail box.

So if it's not temperature related (apparently), what would be the next step/diagnostic I need to take?

Also thank you all for your time to post thus far to help.

 

Check fuel pressure. Sounds like its idleing rough due to unburnt fuel. Maybe something is leaking in your plenum. Test your fuel pressure and post some numbers.

 

Is the only way to check it is to T-off from the fuel line?

I don't have a tester and not sure where to go to get it tested at that won't cost an arm and a leg.

 

You can buy a fuel pressure tester kit at a local auto parts store... they start at about 17 bucks i believe and you can spend all the way into the hundreds of dollars range.

 

Autozone rents them for a steep deposit...but you get all your money back and can use it up to 90 days.

 

If you have a TBI motor then the answer is yes. If you have the CPI motor, then there is a fuel pressure test port on the back of the intake plenum near the brake booster. I doubt you have a TBI motor though. If you have VORTEC written on the top of your motor, then it is the CPI motor.
As stated, any autoparts store will have one. Some let you rent. They come in handy though.