Starts but won't idle
 

1998 Trans at 6.0 LQ4 swapped. Got it started. But it won't idle longer than a minute, sometimes you can feather the gas and it'll stay alive. But won't just idle. It's getting a low signal from the cam sensor code but that's it. I know that won't help but it shouldn't keep it from running. But I could be wrong. I was thinking it could be the security system cutting fuel but it wouldn't be able to stay running with giving it gas then would it? I also thought idle air control solenoid but haven't had the time to check it and see what it looks like. It has been tuned, and it is on its second pcm so it is not a computer thing.

It has been tuned for the swap?

Sounds like you need more base airflow as it warms up. So to me, it seems like the tune isn't right. That's the easiest thing to fix.

Another thing to try would be to open the set screw on the TB up 1/8 or a turn or so. If you have to feather it to stay alive, you need more airflow. Pure and simple.

And the cam sensor doesn't help, but won't cut off the fuel. It makes startup harder.

And VATS cuts fuel at startup. So it's not that.

It was tuned for the swap and the injectors. But the computer before it had the exact same problem so I don't believe it's computer related. I could be wrong. And it also doesn't get better as it gets warm. It does the same thing no matter what. But it has idled perfectly on its own a few times for a minute or 2 but it always ends up dying

And, fuel psi is?
Data log it.

28-35 but 98's are known for low pressure

Put a mechanical fuel pressure gauge on it. Although I had a bleeding line from the pump to the hat in my fuel basket, and it made starting hard... it would idle once the pump was primed. It would just lean out up top.

The other things to check are the coils/plugs and make sure you're getting sufficient spark.

Always start with the big 3 - fuel, air, and spark. And troubleshoot each before moving to the next.

I just tightened that screw on the TB. Don't wanna start it yet because there's a blown fuse. I'm going to get a new fuse and possibly an IAC motor just to be sure. If this doesn't work I'll go to fuel and then coils. I'll let you know how it goes when I get back

I wouldn't tighten it - I'd open it up more. Typically when the motor warms up, the IAC motor closes down... so at cold start you may have sufficient airflow to keep it alive, but as it warms up and the IAC counts start to drop, it may drop too much and kill it.

So I'd open the TB some more to allow the IAC some control over the idle.

Huh??
 

:confused:

we got it. Maf sensor was bad. We unplugged it and it ran completely fine. Bought a new one and it solved our problems.

98's are weird. They have low pressure at the rails. I've seen them hot idle at 40psi

You need to fix this asap. And no it's not common nor is ok to run that low.

You'll need 53-58 psi to run right

LOL. No they don't. They have normal 4 bar fuel pressure.