I’ve got an early 99 PowerStroke that is having rough idle issues. I’ve finally got the truck to start, but after a minute or two idling, POOF, I’ve got a rough idle. Shut the engine down, pause, restart and idles fine. A short while later, POOF, rough idle just like before. This is real consistent, and aggravating as this is my daily driver and tow vehicle.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o></o>
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The back story is, and I’ll try to keep it short, about three weeks ago I decided to locate and fix an oil leak that I was having. The truck used about 3 quarts in one trip to the races and back (about 250 miles). I started by washing the engine and engine bay so that I could trace the source of the leak, drove the truck home about 15 miles with no troubles and started the planned maintenance. Brakes, rotate tires, and locate the leak. After I was done over a busy weekend, I went to leave for work Monday morning and the truck lacked power, started running poorly and the SES came on. So I turned around for home and then the truck started running fine. So, I turned around again to go to work and the truck started running bad again, the SES came on and then the engine stalled. Now the engine would not restart. Checked the fuses, looked for anything amiss under the hood, nothing. After work, I got a friend to pull me home the two miles or less so that I can start working on the truck. <o></o>
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After some fussing, I finally got the truck to run after replacing the CPS (I doubt it), a GPR (took it apart and the contacts were severely corroded and pitted, but I doubt this was the problem) and replacing the computer. Once I replaced the computer, I was finally able to get the truck to run kind of OK, but holy cow, I thought the pistons were going to come out through the heads. I did some more work and I torqued the rocker arm stands, injectors, did the quarter fix on the UVWH and even though it’s running a better, the truck is still not running right and I’m reluctant to drive it in fear of doing further damage. <o></o>
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What is happening right now is that I can start the truck and it will idle fine, but after a short while, the idle will suddenly get real choppy and rough. I can shut the engine down, pause for a few seconds, restart and the engine will idle fine, but again start idling rough like before. The truck is acting like something is getting to a certain temperature or something is timing out.<o></o>
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The truck is an early 99 and the only modifications are the updated filter box and a <?xml:namespace prefix = st1 ns = "mitelunifiedcommunicatorsmarttag/smarttagmodule" /><st1:MySmartTag w:st="on">2000</st1:MySmartTag> computer to replace the bad original computer.<o></o>

 

UVC harness... One side or the other is loose or shorted out.

 

Ok, I finally got some time on my truck. Upon recommendation from a local expert, I tried unplugging the Fuel Pressure Regulator. I unplugged the FPR and then tried starting the truck. The truck would crank forever, but nothing. So I plugged the FPR back in and the truck started right up. After about a minute or two, the truck started idling rough again. I then tried unplugging the FPR while the truck was running and the engine stopped, just like I switched off the ignition switch. Tried it again just to be sure it wasn't a fluke with the same result. I then started the truck and when it started idling rough again, I unplugged the Injector Control Pressure (?) sensor while the truck was running rough and sure enough, the idle smoothed right out. I checked the plug and the sensor looking for oil, but I didn't find any. Would this mean that all I need is new ICP sensor, or is there something else this is telling me?

Thanks for your help, I'm looking to make it to the last couple of races this year.

 

You were likely not unplugging the FPR(Fuel Pressure Regulator) as it is a mechanical part on the fuel bowl.

What you were unplugging, likely, was the IPR(Injection Pressure Regulator) and if you unplug it, the motor will stop running since it uses a electrical solenoid to hold a valve open to allow oil to flow to the injectors through frequency modulation.

When you unplug the ICP the PCM runs a default table of values for the ICP. Usually oil in the sensor is the first sign of a failed or biased sensor.

What codes are you getting with the SES light? That will help pinpoint where to look.

You could try replacing the sensor, although ideally I would personally like to view live data to validate it as I believe your issue would more likely be an IPR or as Joe said shorted Harness.

 

Any smoke while the truck is idling rough? Do you have a way to check fuel pressure? I ask because you might have clogging screens in the mixing chamber in the fuel tank. The screens clog over time and air gets introduced into the fuel system also known as the hutch mod.

 

The seal in the big connector (41 pin...I can never remember how many) may be bad and wet in there now. If u decide to clean, disconnect the batteries first. Its interesting and prob bad if u do no. I think he said in his op he did the 50 cent mod.

 

I know he said he did the 50 cent mod but he washed the engine compartment. If too much water got into the valley then some of that water could have made it into one of the connectors going into the valve covers. Unplug the connector going into each valve cover on the outside of the valve covers and blow them out with air. Ensure you wear eye protection and that you do not blow the gasket for the electrical plug across the universe or valley for that mattter. It will not take too long and it is free to do.