93 K1500 5.7 erratic idle on first start.

[Mike Redding]

Hello,

 

I have a 1993 K1500 with a stock 5.7 6-month old GM long block. Every day when i first start the truck it fires right up and starts to idle erratically for about a minute and runs fine after. I can let the truck sit all day and fire it up again and its fine. I was a certified master John Deere Ag mechanic for 6 years so i know my way around a multimeter and torue wrench but i'm in no way a seasoned auto mechanic.

 

The problem started a few weeks after i installed the long block. For the install i rebuilt the TBI and replaced the fuel pump and all engine sensors. For replacement parts i used ACDelco when available but i have a few things like the IAC and TPS that are some off brand from Orileys but test out ok. Yes the EGR valve is a new ACDelco.

 

The first thing that comes to mind when i see a problem like this is to check the CTS, EGR, IAC, and fuel pressure. Everything checks out fine and its pulling the correct amount of vacuum. I uploaded this video of me starting the truck today for the first time. Some days it will idle for about 10 seconds before it starts to run rough. I'm sure its from the truck going from closed/open loop.

 

The truck has been at two different local shops but neither could find the problem.

[ifixedit]

Have you checked to be sure it has the correct PCV valve? The wrong one can cause all kinds of idle issues. I believe yours should have the one that's empty inside and has just a very small hole to allow the vacuum through.

[Mike Redding]

Just to close this out, I found the problem. The right side intake gasket was leaking around the bottom of the EGR port and sucking oil from the valley. Intake was not warped so I just installed it again and so far so good.