High idle/Self Accelerating
Thread Starter
|
7th Gear
Joined: May 2026
Posts: 7
Likes: 4
High idle/Self Accelerating
I was recommended to cross post this from the Excursion/99-16 forum.
I posted this in the Excursion sub several days ago and haven't gotten any replies, so I figured I would cross post it here to see if anyone has any idea.
Long time lurker, first time poster. This website has been so helpful with little things here and there I've done to my Ex over the years, but I finally ran into a problem I can't exactly solve.
So, I'm not new to wrenching, but I know where there is gaps in my knowledge and one of those is pretty much anything with the voodoo magic we humans call electrical. I know it either works or it doesn't but trying to narrow down electrical concerns has always been a shortcoming of mine. I can connect wire from here to there and know enough to not kill myself or let the smoke out (most of the time). With that said, I acquired a new to me, 2nd Ex, (V10, 4wd, '03) about a month ago and took care of all of the low hanging mechanical issues, but one that has been on the back of my mind is how high the truck revs at start up cold or hot. Cold im used to, but when its hot it still revs up over 2000-2500 and high idles for 10 or 15 seconds before settling to \~800rpm. My first thought was maybe the IAC, but it doesn't show any other symptoms of a failing valve. Then while driving I noticed that it shifts a little more firm, and at higher speeds than my 2000 v10. Additionally when coasting down a hill it seems to not want to go into fuel cut off. And randomly it will actually accelerate down hill. Then coming to stops it will down shift and pull ever so slightly. Once stopped it will pull like im giving it throttle and then after maybe 3 seconds go back to a normal idle. That last bit is very random. Fast forward to last weekend and I installed an android head unit and finally got the torque app running. I have it connected via USB (same dongel I used for forscan). While I havent monitored it with forscan yet (need go renew the license), I noticed a few things that maybe made me point towards the TPS. First was the instantaneous mpg gauge and current fuel consumption through torque. While I know this is mostly unreliable, while coasting down hill at around 55-60 mph, the mpg gauge only goes to about 35mpg and fuel consumption shows about 1.9 gallons per hour. My assumption is that under fuel cut off coasting down a hill that the mpg should be maxing the gauge and the consumption should be all but zero. So I look at my TPS gauge and it reads about 21.5% at idle and 94% at wot (engine off) and my short/long term fuel trims are trying to lean things out to the tune of -5-7%. While this all seems normal, under any throttle while accelerating or cruising the fuel trims are near 0 where I expect them. Since TPS's are cheap, i replaced it yesterday and noticed i have to rotate it before i install it, like im preloading it. As far as I know the truck has no tune, but it has a k&n kit on it and previous owners have installed everything from subs to car alarms and remote starters so who knows what else they've messed with.. i checked the throttle butterflies and cleaned them. There is no binding and the plates fully close on the stop set screw, which does to look like its been messed with.
Do any of you think im on to something? Where can I start chasing issues? Everything seems to be functioning as designed and there are no real driveability issues outside the very random pulling under braking/decel. This one kind of has me stumped and I don't want to go messing with that idle set screw. I guess I could swap the throttle body from my 2000 to test, but I hate to caniblize my 00' if there might be something obvious to someone here. Sorry for the long read. Appreciate everything.
I posted this in the Excursion sub several days ago and haven't gotten any replies, so I figured I would cross post it here to see if anyone has any idea.
Long time lurker, first time poster. This website has been so helpful with little things here and there I've done to my Ex over the years, but I finally ran into a problem I can't exactly solve.
So, I'm not new to wrenching, but I know where there is gaps in my knowledge and one of those is pretty much anything with the voodoo magic we humans call electrical. I know it either works or it doesn't but trying to narrow down electrical concerns has always been a shortcoming of mine. I can connect wire from here to there and know enough to not kill myself or let the smoke out (most of the time). With that said, I acquired a new to me, 2nd Ex, (V10, 4wd, '03) about a month ago and took care of all of the low hanging mechanical issues, but one that has been on the back of my mind is how high the truck revs at start up cold or hot. Cold im used to, but when its hot it still revs up over 2000-2500 and high idles for 10 or 15 seconds before settling to \~800rpm. My first thought was maybe the IAC, but it doesn't show any other symptoms of a failing valve. Then while driving I noticed that it shifts a little more firm, and at higher speeds than my 2000 v10. Additionally when coasting down a hill it seems to not want to go into fuel cut off. And randomly it will actually accelerate down hill. Then coming to stops it will down shift and pull ever so slightly. Once stopped it will pull like im giving it throttle and then after maybe 3 seconds go back to a normal idle. That last bit is very random. Fast forward to last weekend and I installed an android head unit and finally got the torque app running. I have it connected via USB (same dongel I used for forscan). While I havent monitored it with forscan yet (need go renew the license), I noticed a few things that maybe made me point towards the TPS. First was the instantaneous mpg gauge and current fuel consumption through torque. While I know this is mostly unreliable, while coasting down hill at around 55-60 mph, the mpg gauge only goes to about 35mpg and fuel consumption shows about 1.9 gallons per hour. My assumption is that under fuel cut off coasting down a hill that the mpg should be maxing the gauge and the consumption should be all but zero. So I look at my TPS gauge and it reads about 21.5% at idle and 94% at wot (engine off) and my short/long term fuel trims are trying to lean things out to the tune of -5-7%. While this all seems normal, under any throttle while accelerating or cruising the fuel trims are near 0 where I expect them. Since TPS's are cheap, i replaced it yesterday and noticed i have to rotate it before i install it, like im preloading it. As far as I know the truck has no tune, but it has a k&n kit on it and previous owners have installed everything from subs to car alarms and remote starters so who knows what else they've messed with.. i checked the throttle butterflies and cleaned them. There is no binding and the plates fully close on the stop set screw, which does to look like its been messed with.
Do any of you think im on to something? Where can I start chasing issues? Everything seems to be functioning as designed and there are no real driveability issues outside the very random pulling under braking/decel. This one kind of has me stumped and I don't want to go messing with that idle set screw. I guess I could swap the throttle body from my 2000 to test, but I hate to caniblize my 00' if there might be something obvious to someone here. Sorry for the long read. Appreciate everything.
Hotshot
Joined: Jan 2004
Posts: 19,762
Likes: 1,079
From: St Louis
Your TPS readings were completely normal. Put the old one back on.
In order:
1. Inspect the PCV valve and hose looking for vacuum leaks. Probably not if your fuel trims are under control, especially at idle.
2. Replace the IAC valve. Cleaning it sometimes works but that's usually a very temporary "fix".
3. Perform an idle re-learn.
Note that the IAC is actually a computer modulated, controlled "vacuum leak" around the throttle plate.
In order:
1. Inspect the PCV valve and hose looking for vacuum leaks. Probably not if your fuel trims are under control, especially at idle.
2. Replace the IAC valve. Cleaning it sometimes works but that's usually a very temporary "fix".
3. Perform an idle re-learn.
Note that the IAC is actually a computer modulated, controlled "vacuum leak" around the throttle plate.
Thread Starter
|
7th Gear
Joined: May 2026
Posts: 7
Likes: 4
Your TPS readings were completely normal. Put the old one back on.
In order:
1. Inspect the PCV valve and hose looking for vacuum leaks. Probably not if your fuel trims are under control, especially at idle.
2. Replace the IAC valve. Cleaning it sometimes works but that's usually a very temporary "fix".
3. Perform an idle re-learn.
Note that the IAC is actually a computer modulated, controlled "vacuum leak" around the throttle plate.
In order:
1. Inspect the PCV valve and hose looking for vacuum leaks. Probably not if your fuel trims are under control, especially at idle.
2. Replace the IAC valve. Cleaning it sometimes works but that's usually a very temporary "fix".
3. Perform an idle re-learn.
Note that the IAC is actually a computer modulated, controlled "vacuum leak" around the throttle plate.
I'll report back in about a week when I can get to it.
Thank you!
Thread Starter
|
7th Gear
Joined: May 2026
Posts: 7
Likes: 4
I replaced the IAC a few days ago. It was definitely nasty, but still moved freely. Once replaced I performed the idle relearn. As far as the idle goes, it is improved as is the decel to a point. I still don't think it's going into fuel cut off at high speeds all of the time. I notice my STFT go to 0 when slowing down most of the time but it is not 100%. Both fuel trims are still leaning out the mixture more than I would like to see.
Having 336k on it and not knowing the full history I am just going to throw a bunch of parts at it maintenance wise, mainly for peace of mind. The cat is gone, so I'm going to replace that, new O2 sensors, new fuel filter and throw a few cans of BG 44k at it as I have had GREAT experience with that in the past for cleaning injectors, worst case it wouldn't be the end of the world to replace those as, again, they are 23 years old with 336k on them and owe the truck nothing at this point.
Having 336k on it and not knowing the full history I am just going to throw a bunch of parts at it maintenance wise, mainly for peace of mind. The cat is gone, so I'm going to replace that, new O2 sensors, new fuel filter and throw a few cans of BG 44k at it as I have had GREAT experience with that in the past for cleaning injectors, worst case it wouldn't be the end of the world to replace those as, again, they are 23 years old with 336k on them and owe the truck nothing at this point.
Thread
Thread Starter
Forum
Replies
Last Post
AKHunter93
1994.5 - 1997 7.3L Power Stroke Diesel
48
May 29, 2017 08:45 AM
makemeknowit
Modular V10 (6.8l)
18
Nov 4, 2014 03:15 PM
