I've been trying to figure out two codes for about a year now. P0171 and P0174. I've changed fuel filters. Air idle control. Air filter. An elbow vacuum hose. Changed plugs and wires. (Now may be a good time to mention I have absolutely no troubleshooting skills-if someone can tell me what part is bad I can change it but I cannot figure out what's causing the problems). Last week I found out I have two more codes. P1131 and P1151. Plus cylinder 5 misfire. The problem with my truck is when I'm idling it idles rough. Like at red lights or in a drive thru. It revs up like its going to take off-have to hold my foot securely on the brake or it will jump. Then the next moment it nearly shuts off. Lights dim. Shakes like crazy. I can put it in neutral and press the gas to raise the rpms and it will stop. I certainly appreciate any help anyone can provide. I've been thinking I should check the voltage on the o2 sensors (upstream). A guy at an express lube says the two latest codes point to the intake manifold or gasket-possibly the isolator bolts. Thank you in advance for any help!!

 

Do you have the 4.2 V6 engine? This sounds like the isolator bolts, which is a common problem with this engine.. Had the almost identical problem about a year ago. Had to have the isolator bolts replaced.

 

Here is a picture of what they are asking about. This happened on my BILs 4.2. Sounds almost the same. https://www.google.com/search?q=isol...iw=768&bih=928

 

Yes it is the 4.2 V6. Thank you so much!!! I will look into this and start there!