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Hello. I have been having intermittent idle problems where it will drop to around 500rpm and then jump up to around 800rpm before settling back around 680rpm (the normal idle). I finally got it to happen with FORScan hooked up and monitoring it so I got that file I will attach to hopefully give you more info than I can think to type. The only obvious problem I saw is the cam sensor level always reads low no matter what. I have 2 spares in the glovebox I tried out to see if it changed and it didn't. It seems to happen more when it's at operating temp. Never really seems to do it when cold.
Truck info:
2003 f250 with the 7.3
About 250k miles (give or take because of the oversize tires)
Brand new CPS sensor motorcraft part number F4TZ-12K073-C
No oil in the icp plug
IPR nut is on there and snug
No tune or aftermarket injectors
Hopefully you guys can see something I didn't because I'm running out of ideas.
Thanks
I've not had luck with that cam sensor PID - I'd say don't worry about it. PIDs that work on the 7.3 are listed in the FORScan Q&A sticky thread at the top of the forum.
That idle is certainly rough - starts relatively smooth and then ouch.
I'd unplug the ICP sensor and drive it - see if the idle remains smooth. You can drive it that way several days if you need to. If it does idle smooth, the ICP sensor is suspect, even with no oil in the connector.
If still rough, I'd clean and reseal the IPR valve. Then see how she runs.
How does the truck drive otherwise? Good power when on the go pedal?
How does the truck drive otherwise? Good power when on the go pedal?[/QUOTE]
It's a 7.3 so... it's a slow old girl but it drives perfectly. I don't notice any power drops while driving around. Just really weird idle. I tried unplugging the icp a year or two ago and I don't remember how the idle was when I did that, but it did start making a really weird knocking sound which scared me because I thought it was a rod knock but it went away when I plugged the icp back in. Fuel knock maybe? Idk how unplugging the icp would cause that though. I'll try unplugging it again tomorrow after its warmed up and see if that idle problem goes away and listen for that knocking sound.
Edit: I forgot to mention the idle also drops really low every now and then when I'm backing into my somewhat steep driveway. When I get backed up all the way and let off the pedal it'll drop to around 500rpm and sound like I put a lope tune on it for a couple seconds and then recover.
Update: I put the truck in park when I got to where I was going and the idle was all over the place again. Unplugged the ICP and it smoothed out perfectly other than when the AC kicked on and off and it moved a couple rpm. That knocking sound I mentioned in my reply also came back and from the videos I can find on YouTube it sounds like a fuel knock. I attached it below but it's hard to hear over the truck running. If that is a fuel knock why would unplugging the ICP cause that? And if it's not what else could it be?
Edit: The flex plate cover is off in that video because when I first heard it I thought I broke the flex plate somehow and was trying to check it. It's not missing.
Last edited by czweigle; May 20, 2025 at 08:29 PM.
Reason: Added info
Yes, but what does that have to do with the (fuel?) knock? It is only noticeable when the ICP is unplugged or sometimes I'll hear one or two knocks when it first starts but then goes away.
Oh okay, I misread it.
I don't really have anything useful atm. Once you replace the ICP, you can go from there and see how everything looks and run the diag tests and what not.
have you looked at the UVCH's done any other troubleshooting, etc. Wonder if you have any injector issues. I don't think any of that would cause knocking but just throwing stuff out there, lol
I haven't had the time to go through and look at all of the harnesses/pigtails to check for chafing or anything. Something to note however, the truck was stolen TWICE and the second time they had it for almost 3 months and absolutely abused it. Spray painted a black two tone, smashed in both sides from not knowing how to drive a crew cab long bed, slash in one of the tires from running over something, and they had a cheap junk tuner turned basically all the way up so who knows what they did to it. I can't afford a new set of injectors right now so I hope they're ok lol. The only diagnosing I've done so far is unplugging the ICP and swapping the CPS twice just to make sure one wasn't bad from factory.
Well shoot - stolen truck adds another variable or two.
Recommend checking fuel pressure.
Has the oil been changed since it was taken, so you know the quality/weight/time on it? Good oil is critical.
Some other checks - how is blowby? Overturned oil fill cap stay put at idle?
Clean battery connections and verify charging system voltage.
Any codes?
That backing up rpm drop would be low transmission fluid if it was bogging, but if just a lope, that and the rough idle could point to a sticking IPR valve. I think if it was mine, I'd leave the ICP sensor unplugged, purchase an IPR reseal kit, and clean/rebuild the IPR. Then see how she runs.
Well shoot - stolen truck adds another variable or two.
Recommend checking fuel pressure.
Has the oil been changed since it was taken, so you know the quality/weight/time on it? Good oil is critical.
Some other checks - how is blowby? Overturned oil fill cap stay put at idle?
Clean battery connections and verify charging system voltage.
Any codes?
That backing up rpm drop would be low transmission fluid if it was bogging, but if just a lope, that and the rough idle could point to a sticking IPR valve. I think if it was mine, I'd leave the ICP sensor unplugged, purchase an IPR reseal kit, and clean/rebuild the IPR. Then see how she runs.
Is the fuel pressure something I can check with FORScan? And if not how do I go about doing that? I have changed the oil and the filter along with the fuel filter because the fuel bowl was full of silt which I sucked out with a vacuum. I'm running full synthetic 15w40 with 1 bottle of lucas oil stabilizer. It has some haze out of the oil fill cap but the lid will stay on there until it vibrates off. The battery terminals are all tight and clean, system charges at about 13.8 volts. It has an ignition code B1352 from when they destroyed the ignition cylinder and I can't figure out how to get it to go away. Other codes that were in there but maybe old: P1249 and P0603 which I think is from when I disconnected the batteries multiple times switching out cam sensors. I'll look into that ipr rebuild kit and try to get that done soon. It also just started dripping oil out of the front of the engine I think front main seal . Lots to fix thanks to the a$@holes that stole it.
Edit: It wasn't the front main seal. The new CPS I put in was missing a good 1/4 inch of the o ring and the oil was just spraying out around it onto the harmonic balancer. That just saved a good $800 in labor.
in the tech folder there’s a fuel pressure testing guide. It’s really well put together and has a list of the parts you’ll need including part numbers.
in the tech folder there’s a fuel pressure testing guide. It’s really well put together and has a list of the parts you’ll need including part numbers.
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Random Idle Issues
it's a slow old girl but it drives perfectly. I don't notice any power drops while driving around. Just really weird idle. I tried unplugging the icp a year or two ago and I don't remember how the idle was when I did that, but it did start making a really weird knocking sound which scared me because I thought it was a rod knock but it went away when I plugged the icp back in. Fuel knock maybe? Idk how unplugging the icp would cause that though. I'll try unplugging it again tomorrow after its warmed up and see if that idle problem goes away and listen for that knocking sound.
Update with video of sound
. Lots to fix thanks to the a$@holes that stole it.
