markes12344

I swapped a 5.0 HO long block into my truck, when I did this I also replaced my MAP, throttle position sensor and idle air control. I replaced my egr solenoid and have a new ignition coil, with new spark plugs wires and rotor cap. Re-ran new vacume lines sliding them over the plastic ones at the ends, chopping out the brittle middle parts.

So basically I almost have everything new but a couple solenoids/vacume control valves.

Yet my truck has a rough idle some times at first start,the engine light comes on when going down the high way and i let off the fuel, or roll down a hill.

Plugging it in tonight to pull codes but anyone have any ideas?

qdeezie

You need an IAC bypass plate. The HO camshaft requires more airflow at idle.

sdmartin65

What is vacuum at idle? Was motor new/rebuilt or used?
Reason I ask all this is I have a slightly re ground HO cam and it doesn't take much to make vacuum marginal.

markes12344

Remand block. Not sure what the idle vacuum is, I have no vacuum gauge. The idle bypass plate makes sense for a solution. Engines just starting. Last winter I had my throttle a crack open. Had a different problem, tps voltage high (or low can't remember) this summer I re set my butterfly's to a more closed position. Now it's not able to get enough air.
Still open to ideas and other troubleshooting.

Makes me wonder tho, while traveling wouldn't the idle air control valve close anyways?
Just so I don't thread jack this one, I started one for my problem

qdeezie

You could also check the vacuum tree to ensure it's clear so that your MAP sensor has the best signal possible.