Rough Idle when Warm

[Robert D]

So the K5 is idling high when cold and has +30psi of oil pressure at cold idle. When warmed up, it idles low and has ~15psi of oil pressure (on the gauge). The truck is also missing pretty badly, especially noticeable when its warmed up and idling low (the engine shutters and shakes the truck sometimes). I've replaced the plugs, wires, air filter, pcv valve, TPS, both thermo sensors, and....I'm pretty sure that's it so far. I also ran a can of STP fuel system cleaner and the STP gasoline treatment with the last 2 tanks to see if it might be a dirty system...no difference. I just changed the fuel lines out, but did not change the filter...would it be a good idea to change out the filter as well? I don't think the fuel injectors have been rebuilt/replaced ever (it's a 91 with ~147k mi). Any thoughts?

 

[mtrdrms]

fuel filter couldnt hurt. Any Check Engine Lights?

 

[Robert D]

Oh and the check engine light isn't coming on. I'm going to go mess with some of the vacuum lines behind the air filter to see if they are the culprit.

 

[Robert D]

Just changed the hoses behind the intake. The ones I speak of consist of a T-connector where a plastic vacuum line connects to two rubber lines. The larger diameter rubber line runs to the top of the intake (what is this for?); the other rubber line runs into what appears to be a valve with 3 inputs, one is capped, the other runs to a spherical canister (charcoal canister??). Anyways, the hose was broken at the spot where it connects to the intake manifold...replaced...

 

[opfor2]

Did that solve UR problem ???

 

[Robert D]

I'll know tomorrow as I have not driven it enough to get it warm since Friday.

 

[Robert D]

Now that I've driven the truck more than a half-mile today; I've found the hose replacement did not fix the miss, but the truck does idle higher and keeps the oil pressure around 30 on the gauge??? Weird. I'll probably do the cap/rotor next.