Hey all, just bought my first truck today for $1700, and kinda thinking I got screwed on this one and maybe should've walked away. The engine was rebuilt by a previous owner, who also put in a reman tranny and did a lot of other work. However, it runs pretty rough. Seller thinks the big issue is a vacuum leak, and it has sat for a good while, probably also needs a tune up. Just wondering what to check/replace (and I need a good diagram of the engine bay if you have one). My mechanical skills are okay/intermediate/DIY, but I have only worked on my Audi. Here are my problems from the drive home, which was 50 miles:

• Turns over fine, low RPM idle that eventually stalls.
  
• Stalled at just about every stop/red light.
  
• Rough, slow accel most of the time, but occasionally good throttle with more gas.
  
• Accel pedal sometimes seemed unresponsive
  
• Light acceleration I got a grinding noise.
  
• 50 mile trip, avg 55mph 10 MPG.
  

Other problems that might be related:

• Has 4x4 options, but the front drive shaft is not installed. I drive it in 2wd back home.
  
• Passkey/Security issue - I can only start it in overdrive to bypass (Steering column from Yukon was put in)
  
• Dash instrument cluster - nothing except the battery gauge and occasionally the tachy work. All lights were on during the trip back, but seemed to turn off when I was tinkering at home.
  
• Battery pretty low voltage - I killed it tinkering in my driveway... gotta charge it somehow now.
  

Please help!

After 5:14 in that video, that is pretty close to the grinding sound I mentioned.

I would start with your system voltage first. This can cause run ability issues with the HV ignition system.
Check for any codes. Even pending ones are a good start.
I would verify your timing is correctly set.
PASSKEY isn't the issue. This is just a matter of installing the correct shifter.

Battery voltage is about 8v right now. Not sure if it'* still under warranty. It'* Interstate and there aren't any markings. Going to Autozone to pick up a scanner and PCV valve and some other things. Will take it to have it tested and confirm.

Is that 8v running or off?

Only accessories were running. Took it to auto one they said it was completely bad. I got a new battery. Now instrument cluster appears to be working except oil and temp. Still idling low. Got P0452 codes and some abs codes too.

Engine is turning over, but doesn't start now. I did get it started once. Seems to idle ok for a minute around 1000RPM, then drops to around 500RPM and runs pretty rough. I need to take a look at the gas tank when it'* not raining out. The gas cap didn't look to good the last time I refilled it. Guessing it could be other things - including vac leak.

Changed the oil this morning and replaced PCV. Got it running and drove around the block. Cleaned the spectre air filter and air drying it now. When I put my hand over the air intake where the filter goes, that seems to correct the idling when it drops. So I'm guessing that it definitely is a vacuum leak, or maybe a sensor fail.

So if the Passkey Secure issue isn't resolved, should the instrument panel function properly anyway? I am thinking about replacing that or checking for cracked solder.

Passkey would only disable the starter I think.

What is your current system voltage?