RememberGoliad
Veteran Member
Howdy y'all,
This isn't a 'what do I do about...' post, I've already solved the problem as far as I know. Just posting in case it might help someone else with an un-findable solution to the engine speed creeping up on a warm Excursion or Super Duty Ford pickup/van.
The troublemaker was ol' Blue, our 2003 Expedition 8800GVW (so making it a less-restrictive emissions class when it was built.) It had been acting for months like it had an intermittent vacuum leak. I googled and youtubed and crawled forums for seems like ever, and when I'd go out to check what I'd found, it wouldn't act up. The problem: It'd start and run just fine cold, get down to the hard road through both gates idling just fine when I'd get out to open 'em....around 800 rpm. By the time I get to town, though, it was straining against the brakes and when I'd go into neutral or park, it'd jump to about 1200rpm and gradually, over about 20 seconds, climb to 2000rpm. It wouldn't do this every time, and sometimes at the next errand, it'd do what it was supposed to do. Hard to find a gremlin. It wasn't worse when humid, or when dry, or when hot or cold. I got to where I really dreaded going anywhere on account of empathy for the transmission and converter.
No codes showing, no check engine light, took it to a shop and had 'em put the computer on it, and since they didn't want but another half hour labor to see if they could figure it out, I let 'em. They diagnosed bad alternator. Reasoning was, and I confirmed this, that with that emissions class, if the computer sees low system voltage it'll try to boost it by raising the idle speed. IDK if that was by design or if it was one of them 'retroactive' design claims. Anyhow, I replaced the alternator since it was an O'Reilly lifetime warranty one and they did the swap-out on the strength of me having a piece of paper from a real shop that said it was bad. Nope, that wasn't the problem.... which I didn't think it was anyway but since I was only gonna be out a half hour of my time I did it just for giggles.
A week or so ago I caught it doing its thing as I pulled into the yard here, and didn't have something else urgent to do and was in a cranky mood about it so I popped the hood and went to hunting. Was thinking maybe EGR valve stuck....or its pipe/hose cracked and letting a huge unseen vacuum leak in when the temp around it changed. Started pulling hoses off one by one and looked the pcv valve and thought nah, can't be that one, there's no manifold pressure on it. But right above it was another one from the filtered air (I mean, tee-ing off of the duct that goes from the air filter to the throttle body) that wrapped around back up by the firewall and disappeared into the shadows behind all the plastic. I pulled that one off, and shazam! I found shop-vac style suckage like it was a straight pipe into the intake! When I plugged it with my thumb, engine throttled back to a slow, 'normal' purr. Got all excited, killed the engine and climbed up there and found it going to the idle air control valve.
Knowing me, and how I hate throwing parts at an engine until I win the wannabee-mechanic's lottery, I set out to scientifically prove this valve's brokenness. Pulled it off and checked it physically. Blew in it and zero restriction.... then I stuck a screwdriver in it and manually tried to actuate it. It did, moving about 1/8". Blew again while holding it against its spring and it was sealed against the force of a human exhale. Ok, so mechanically it's doing its thing. Checked resistance across the two pins in the connector. 10.5 ohms. Neither side grounded. Checked Blue's connector with key off, 0V and with key on, 12V. Hmm. Don't know what they're supposed to do. So I obtained a new one from O'Reilly. 10.5 ohms resistance, 1/8" or so of shaft travel, normally open and sealed when held against the spring. So far I had proved....NOTHING. The only difference in measurements and actions of the new and old ones was the dirt and tarnish on the old one.
What the heck. I've got nothing to lose if I don't try it. If it doesn't work I'll clean it back up and take it back. So I put the new one in and put it all back together. Ran like a dream, idled perfectly. Only thing I can think is its spring was getting weak or the electromagnet for the pull was both shorted and open in just the right combination to cause a weak field while keeping the same resistance.
Bottom line is, if you have hunting warm idle problems in one of these old two valve 5.4's, suspect the idle air valve, even if a 'reputable' shop tells you point blank that they tested it and it's fine. (That was the answer I got from the "mechanic" that diagnosed my problem as being a bad alternator.) It's kinda involved to get to the thing but it's really no more than 10-15 minutes and three different wrenches: 8mm and 10mm end wrenches and 8mm socket. Pair of needlenose helps get the throttle spring off. And 8mm is close enough to 5/16" to use it on the gear clamps on the air ductwork.
This isn't a 'what do I do about...' post, I've already solved the problem as far as I know. Just posting in case it might help someone else with an un-findable solution to the engine speed creeping up on a warm Excursion or Super Duty Ford pickup/van.
The troublemaker was ol' Blue, our 2003 Expedition 8800GVW (so making it a less-restrictive emissions class when it was built.) It had been acting for months like it had an intermittent vacuum leak. I googled and youtubed and crawled forums for seems like ever, and when I'd go out to check what I'd found, it wouldn't act up. The problem: It'd start and run just fine cold, get down to the hard road through both gates idling just fine when I'd get out to open 'em....around 800 rpm. By the time I get to town, though, it was straining against the brakes and when I'd go into neutral or park, it'd jump to about 1200rpm and gradually, over about 20 seconds, climb to 2000rpm. It wouldn't do this every time, and sometimes at the next errand, it'd do what it was supposed to do. Hard to find a gremlin. It wasn't worse when humid, or when dry, or when hot or cold. I got to where I really dreaded going anywhere on account of empathy for the transmission and converter.
No codes showing, no check engine light, took it to a shop and had 'em put the computer on it, and since they didn't want but another half hour labor to see if they could figure it out, I let 'em. They diagnosed bad alternator. Reasoning was, and I confirmed this, that with that emissions class, if the computer sees low system voltage it'll try to boost it by raising the idle speed. IDK if that was by design or if it was one of them 'retroactive' design claims. Anyhow, I replaced the alternator since it was an O'Reilly lifetime warranty one and they did the swap-out on the strength of me having a piece of paper from a real shop that said it was bad. Nope, that wasn't the problem.... which I didn't think it was anyway but since I was only gonna be out a half hour of my time I did it just for giggles.
A week or so ago I caught it doing its thing as I pulled into the yard here, and didn't have something else urgent to do and was in a cranky mood about it so I popped the hood and went to hunting. Was thinking maybe EGR valve stuck....or its pipe/hose cracked and letting a huge unseen vacuum leak in when the temp around it changed. Started pulling hoses off one by one and looked the pcv valve and thought nah, can't be that one, there's no manifold pressure on it. But right above it was another one from the filtered air (I mean, tee-ing off of the duct that goes from the air filter to the throttle body) that wrapped around back up by the firewall and disappeared into the shadows behind all the plastic. I pulled that one off, and shazam! I found shop-vac style suckage like it was a straight pipe into the intake! When I plugged it with my thumb, engine throttled back to a slow, 'normal' purr. Got all excited, killed the engine and climbed up there and found it going to the idle air control valve.
Knowing me, and how I hate throwing parts at an engine until I win the wannabee-mechanic's lottery, I set out to scientifically prove this valve's brokenness. Pulled it off and checked it physically. Blew in it and zero restriction.... then I stuck a screwdriver in it and manually tried to actuate it. It did, moving about 1/8". Blew again while holding it against its spring and it was sealed against the force of a human exhale. Ok, so mechanically it's doing its thing. Checked resistance across the two pins in the connector. 10.5 ohms. Neither side grounded. Checked Blue's connector with key off, 0V and with key on, 12V. Hmm. Don't know what they're supposed to do. So I obtained a new one from O'Reilly. 10.5 ohms resistance, 1/8" or so of shaft travel, normally open and sealed when held against the spring. So far I had proved....NOTHING. The only difference in measurements and actions of the new and old ones was the dirt and tarnish on the old one.
What the heck. I've got nothing to lose if I don't try it. If it doesn't work I'll clean it back up and take it back. So I put the new one in and put it all back together. Ran like a dream, idled perfectly. Only thing I can think is its spring was getting weak or the electromagnet for the pull was both shorted and open in just the right combination to cause a weak field while keeping the same resistance.
Bottom line is, if you have hunting warm idle problems in one of these old two valve 5.4's, suspect the idle air valve, even if a 'reputable' shop tells you point blank that they tested it and it's fine. (That was the answer I got from the "mechanic" that diagnosed my problem as being a bad alternator.) It's kinda involved to get to the thing but it's really no more than 10-15 minutes and three different wrenches: 8mm and 10mm end wrenches and 8mm socket. Pair of needlenose helps get the throttle spring off. And 8mm is close enough to 5/16" to use it on the gear clamps on the air ductwork.
