Hey guys
Hoping someone can provide some insight to a strange issue that has come up. My truck, at idle, will rhythmically idle rough. I will feel the truck shake and the idle drop about every 3 or 4 seconds. No codes are being displayed. Things I have tried:
Cleaned throttle body
Idle air control sensor
Map sensor
Plugs, wires, cap and button
Air temp sensor
Cleaned carbon buildup
Last year did timing chain, harmonic balancer, fuel spider injector, fuel pressure regulator and fuel filter, fuel psi is at 49 idle, 47 under load.
Hoping someone has come across something similar. Everything i am trying now is a hail Mary. Any insight would be greatly appreciated.
Thank you

 

Rough idle can take some work to find and fix but that’s what we are here for:

1. Measure fuel pressure at key on and then the 10 minute leak down
2. Do you have a recent compression test?
3. You will need a capable scanner and to start with, get CMP retard with the +/- 2 degree spec

George

 

Thank you George for reaching out. I have tested fuel psi at key on, idle and under load. key on is 50, idle is 49, load is 47.
No compression test but the engine has 387k so i know she is tired
Got a decent scanner but not sure what the CMP retard is that you mentioned. I am not a mechanic but i have turned a few wrenches in my day. lol I did check fuel trim numbers and the long trim is around 7 and stays about the same or drops a bit under load.

 

Your key on fuel pressure is low. What is it ten minutes after key on without starting the truck?

Fuel trims have to be reported together, all 4 values: STFTB1, LTFTB1, STFTB2, LTFTB2.

George

 

not sure if this new info will help but the idle will "lope" about every 3 to 4 seconds. Idle will be at 700, then a quick shudder and drop to around 4, then pops back up. This happens consistently when warned up. Also significant increase in issue with the AC on or if engaging power steering

 

my apologies George i did not check all the trims at the same time. I will check that tonight. I also did not do a 10 mins after key with the pressure tester

 

I think i might have found the issue George. Going over some things i did for the fire last year i realized i did not replace the plug behind the steering shaft. I did that on Sat. Well in the process of doing that i realized the plug wire for the cylinder closest to the firewall, was laying on the heat shield and was discolored. I replaced that and the other plug, and seems to be running pretty good now. Will continue to monitor but wanted to thank you for reaching out and providing guidance. Its guys like you that make these sites so helpful. You rock young man !!!

 

Glad your fixed up


George