Rough Idle
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5th Wheeling
Joined: Dec 2024
Posts: 34
Likes: 9
From: NW FL
Thanks! I’ll probably order an IPR then. I’ll inspect my lines as well, could be I didn’t do a great job when installing the driven diesel in tank filter delete.
she’s a 4x4 SRW CCSB Lariat
she’s a 4x4 SRW CCSB Lariat
Last edited by woody18; Nov 11, 2025 at 09:34 PM.
It's a Van Gogh
Joined: Feb 2010
Posts: 7,813
Likes: 1,335
From: Elk Grove, CA
Looking at those 2 WOT files, it does look like ICP is lower than normal, but the PCM is adding PW, and the rig is performing well. You could change out the IPR and see if your rough idle smooths out. Checking for fuel aeration is another possible cause - usually from the fuel line connections between the tank and frame rail pump ( the suck side).
I measured your 20-60mph time on WOT 1, and it's 7.6 seconds, good for an empty truck on a stock tune. What is your truck's cab and bed size? Wanted to get an idea of the weight.
I measured your 20-60mph time on WOT 1, and it's 7.6 seconds, good for an empty truck on a stock tune. What is your truck's cab and bed size? Wanted to get an idea of the weight.
I learn something new every time.
Gonna buy you a beer some day.
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5th Wheeling
Joined: Dec 2024
Posts: 34
Likes: 9
From: NW FL
New IPR fixed the stumble at idle or at least it feels like it. Need to gather some data on my fore scan to see if the data reflects what my butt dyno tells me. I’ll post the CSV whenever I get one! Thanks for the help troubleshooting.
Lead Driver
Joined: Jun 2013
Posts: 5,648
Likes: 893
From: north of Minneapolis, MN
I had noticed a barely noticeable rhythmic variation at idle on mine. I really just thought is was the 400k miles catching up to it. But then towing the horse trailer through Des Moines...the HPOP failed, leaving me stranded. I had installed a new IPR 3 years ago.
Laughing Gas
Joined: Jun 2017
Posts: 835
Likes: 125
From: CSRA, SC
Looking forward to that data!
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5th Wheeling
Joined: Dec 2024
Posts: 34
Likes: 9
From: NW FL
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It's a Van Gogh
Joined: Feb 2010
Posts: 7,813
Likes: 1,335
From: Elk Grove, CA
If it clears up when the ICP is unplugged that's a good sign the wiring is fine, but the ICP is not.
Any oil on the connector? If so clean it up with some spray contact cleaner and reuse.
Then get a new ICP from a trusted source like Riff Raff or Diesel O Rings.
Any oil on the connector? If so clean it up with some spray contact cleaner and reuse.
Then get a new ICP from a trusted source like Riff Raff or Diesel O Rings.
Thread Starter
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5th Wheeling
Joined: Dec 2024
Posts: 34
Likes: 9
From: NW FL
New ICP from Diesel O Rings. No real change. Truck performed well on 3400 mile road trip up to altitude in Colorado. Had extreme difficulty starting despite new Mitsubishi stock style starter, new GPR and New battery Cables. Here’s some data at altitude and recently with a load. Thinking injectors may just be worn out as best I can tell they are originals.
Last edited by woody18; Jan 28, 2026 at 08:20 AM.
Lead Driver
Joined: Jul 2017
Posts: 6,860
Likes: 2,335
From: WV
Been following along but haven’t had anything helpful to offer.
Nice Mustang in your profile photo!
Trouble starting could be GPR related. You can try crossing the large terminals for 30 seconds (more or less) immediately before cranking to see if it helps.
Otherwise 5w-40 helped mine start more quickly. Not sure how that may affect your wandering idle though.
Nice Mustang in your profile photo!
Trouble starting could be GPR related. You can try crossing the large terminals for 30 seconds (more or less) immediately before cranking to see if it helps.
Otherwise 5w-40 helped mine start more quickly. Not sure how that may affect your wandering idle though.
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5th Wheeling
Joined: Dec 2024
Posts: 34
Likes: 9
From: NW FL
Thanks! It’s a ‘22 GT500, my uncles but I get to drive it. Pushing about 900 to the wheels as we increased the blower size and it’s running on E85. Been having issues with it hooking up, all that fancy technology doesn’t like the additional power and the big slicks.
I currently am running 5W-40 and made the switch for that very reason, I will check the GPR again but now that I’ve done some more searching I think maybe I was simply asking too much of the truck when it had trouble starting. It was 0 degrees ambient temp at 9000’ elevation. This morning it was 26 deg here at sea level at home and it cranked absolutely no problem.
I currently am running 5W-40 and made the switch for that very reason, I will check the GPR again but now that I’ve done some more searching I think maybe I was simply asking too much of the truck when it had trouble starting. It was 0 degrees ambient temp at 9000’ elevation. This morning it was 26 deg here at sea level at home and it cranked absolutely no problem.
Hotshot
Joined: Dec 2012
Posts: 11,276
Likes: 1,657
From: Las Cruces New Mexico
Get a quart of 2 stroke oil, add some 2 stroke oil directly into the fuel bowl maybe a quarter of the way and the rest in the fuel tank, that helped my 00 a bit when it it had old injectors. Could also be worn out injectors causing hard cold starts and smoke, you could probably prolong them a little more if short on dinero by shimming them.
Also you mentioned oil loss, does the truck have serious blow by? Has the injector O rings ever been replaced? IMO like I previously mentioned you might want to at least get new injector O rings and shim them in the bench and see if the oil consumption goes down and your hard hot starts goes away.
Also you mentioned oil loss, does the truck have serious blow by? Has the injector O rings ever been replaced? IMO like I previously mentioned you might want to at least get new injector O rings and shim them in the bench and see if the oil consumption goes down and your hard hot starts goes away.