P1506 Code - High starting idle - 99' 4.0 SOHC

[koda2000]

i'd go ahead and swap the TCS as the reading was higher than what it's supposed to be. will it start/run/idle with the TCS disconnected? i don't know, never tried it...

 

[taylorpro]

i'd go ahead and swap the TCS as the reading was higher than what it's supposed to be. will it start/run/idle with the TCS disconnected? i don't know, never tried it...

im going to try it. worth a shot since its such an easy swap. if that doesnt fix it im just gonna say eff it until i pull the engine in a few months to change the chains. ill do new gaskets and vacuum lines at that time if need be.

I dont think it will run without the TPS though

 

[koda2000]

im going to try it. worth a shot since its such an easy swap. if that doesnt fix it im just gonna say eff it until i pull the engine in a few months to change the chains. ill do new gaskets and vacuum lines at that time if need be.

I dont think it will run without the TPS though

of course i meant TPS, but you knew what i meant (senior moment) and yes, it may not run w/out it connected, but easy to try. the pcm may think it's at idle or it may think there's something wrong.

 

[taylorpro]

of course i meant TPS, but you knew what i meant (senior moment) and yes, it may not run w/out it connected, but easy to try. the pcm may think it's at idle or it may think there's something wrong.

I'm going to be trying a new TPS today i believe

 

[taylorpro]

tried a new TPS and no change was noticed. Thinking its more than likely gotta be a vacuum leak somewhere. Just don't know what else could cause it. It's not a rough idle. There's no CEL's or obvious signs that somethings malfunctioning. It just idle's high. And the startup idle is rediculous

 

[2000StreetRod]

leaking intake gaskets

Perhaps your intake gaskets are leaking and the weather just happened to get cold when you added the alternator. See: Starting my 00M12 Installation

 

[taylorpro]

**** man that sounds like my problem in general. the whole deal. like i said the idle isnt terribly high itself. 9-1000rpm. but the cold start up flare is what scares me. I wonder if just replacing all the intake gaskets would reduce the flare? Or do you believe the new tensioner helped with that as well?

I have another question about this line at the end of the main post "The second start up was much quieter so the installation of the oil drain restrictor was worth the cost and effort". What is the oil drain restrictor you added? What does it do?

 

[2000StreetRod]

cold start flare

The tensioner should have no impact on the cold start flare. The restrictor is the pencil shaped plastic item that reduces the volume of the oil chamber that feeds the front tensioner. The reduced volume means the oil pressure comes up faster at engine start. It also would not have any impact on the cold start flare. If your engine still has the original upper and lower intake gaskets then dry/shrunk gaskets could allow air into the cylinders that bypasses the throttle plate and the IAC valve. It's fairly common on the older SOHC V6 engines.

 

[taylorpro]

Okay thanks man. Ill prob just wait it out with this line ive got on there now. It works well enough. Over winter break ill get that kit and go through all of that stuff. I think it will help me with startup rattle as it did you as well. Thanks for all the help man

 

[drdoom]

Taylor have you tried the IAC hard pipe restrictor mod? I use it and helps a little bit with the surge. All it is a one inch length of 11/32" transmission cooler line, jammed into the intake end of the hard pipe. Not much, but might be worth a shot.

PS: You know, come to think of it, my Taurus idles up worse than the Explorer...always something.

 

[faller]

P1506 Idle Air Control Over Speed Error

I also have a 99' 4.0 SOHC and the exact same symptoms. I replaced the IAC and there was no change. I'm thinking vacuum leak or possibly leaking intake gaskets. I'm going to do the pvc and tubes. Then check really good for vacuum leaks and test the IAC again because I read another post where a guys said his new IAC was faulty so I haven't ruled that out yet.

As a side note I had the leaking intake gasket problem when I got the truck. It ran rough as hell on real cold days at start up and would stall if not given gas. It didn't rev high like it's doing now. Once it warmed up it was okay. It never threw a code either. Doesn't mean that we might not have intake leaks with different symptoms but I just figured I add that info to this mystery. Also I replaced the gaskets which cured that problem. That was about three years ago so I wouldn't think I was due again. Because it happened to you when you were messing around in there I'd be inclined to lean more toward vacuum leaks. My pvc valve seemed loose at the T when I just checked it. That's why I'm going to start there. It is original too with 100,000 miles so it's due. Please update if you figure yours out. I'll be sure to do the same.

 

[faller]

It was the IAC.

I tested the IAC for all the electrical stuff and it passed. When I replaced it last winter it got better for a few days then went back to doing the same thing. It didn't do it all the time before either so I assumed no change. Anyway, I swore it was going to be a vacuum leak and I was researching building a smoke machine. In the mean time I figured I'd do the pcv and I also put in a new air filter. When I messed with the pcv a few days ago things got worse. It idled rough etc. One of the new symptoms was the vacuum cleaner sound coming from the air filter. I started searching for that symptom on this forum and it pointed again to the IAC. I just wouldn't believe it. Sure enough I pulled the tube from the IAC where it attaches to the intake tube and I found that the sound was now coming from that tube ...and it only goes to the IAC. Soooo lucky for me I saved the old IAC that I had cleaned up. I tried just cleaning it before and it didn't work right that's why I got the new one. Anyway, I switched them and voilà! It runs like a champ again. I disconnected the battery for a while to reset the whatever you call it because I learned on here that that's what your supposed to do. I saved the IAC again as it passed all the electrical tests and mechanically seems fine. I can only say that it could be the seal below the IAC and maybe changing them cleared it up for now or it's just that they need to be constantly cleaned. ...or both. I'm sure this is not the end of this for me but it will just be a maintenance issue really. I'm lucky the fog horn vacuum cleaner sound came on or I never would have figured IAC this soon. I was just so convinced that it couldn't be.

Do the tests with a multimeter on yours. If it passes them all. Unplug it while it's running and see if there's any change. If there is then it's okay but so was mine so take it off anyway and clean it. move the gaskets (rubberized seal) around on the bottom if they come off stuck to it and make sure there's a good seal going on there when you put it back on. Get a new seal if you have to. Mine was pretty new because the IAC was fairly new. Put it back on snug but don't strip those puppies in the plastic. That's all I can tell you. It worked for me. Same truck, same symptoms. I didn't touch anything else. Actually, I did. I replaced the pcv and the air filter. The pcv was definitely bad and I'm sure the air filter was too but the truck ran the same until I switched the IAC.

 

[faller]

I re-read the thread and I see that you've tried replacing the IAC already. It might just be the seal underneath. It's defiantly something to do with that piece if crap. the code says so and it's that tube that you messed with when your problems started. Test it again. Make sure it's sealed. Clean it. Make sure the tube is clear. Pull it off and put it back on. Throw it against the wall and swear at it. I know it doesn't seem like it could be that ...but that's what it is. You could smoke test the intake and vacuum lines. That wouldn't hurt ....but it's the IAC.

 

[taylorpro]

yeah im doing a long block swap in about a month since i'm having timing chain guide issues anyway. I'm going to clean it out and go through the pcv and all the vacuum stuff when i do. as well as put a new IAC gasket on there, and new intake gaskets. I think replacing all the seals, the pcv valve, and checking the vacuum line's im basically taking care of all possibilities. Again, it NEVER idle's rough. EVER. It idle's perfect, just about 300rpm to high; that and the startup spike is ~2000rpm

 

[faller]

I hate to embarrass myself after being so sure in my other posts but I figure it's only fair to update. About a week or two later the light came back on. Same code. I figured I'd clean the newer IAC that I had which was off the vehicle and put it back on. During the cleaning I broke the plunger doohickey that seats the valve. So I figured I needed a new one anyway because the original was on the vehicle. So I cleaned the original and reinstalled it. Didn't see any difference. Went to Autozone because their IAC has a lifetime warranty. So did the one I broke from Pep Boys. Lesson learned. I won't clean them anymore. If they don't work I'm returning them. Anyway, on the trip home the light came on, same code 1506. Put the new one on and no difference. Haven't driven it far enough to make the light return yet but I'm sure it will. I suspect a vacuum leak. Oh yeah after that I did clean the MAF, no change. I know you're doing your big project on your truck but I figured I'd keep posting on here what ever I find out. At this point the inspection sticker is expired on mine so I may throw in the towel and let the pros find the problem. I'm not on here often but I will come back and post anything I find if I do go that route. I really want to smoke this puppy to eliminate leaks but I'm out of time. So building a smoker at this point seems like an exercise in frustration. Going to the stealership would obviously be expensive but probably be the best option to find out the real cause. As I said if I do I'll make sure they tell me what they did and report back.

 

[faller]

Redeemed.... for sure this time

So I finally got it. This is gonna sound ridiculous but the fix was to turn back the idle screw. Duh! It idles too fast. It's the last thing you would think of doing because why or how did it get turned the other way? I have an answer for that too. Normally there would be no reason to go there so I never did. But if you're bored and you like to read I'll tell you how I got there because there is a bit more to it. I read a guy's (javi2001) post on another forum describing how he fixed his and it was the tps. All credit goes to him. I wouldn't have figured this out without his post. According to him the IAC is triggered once the tps voltage is above 1.1 So I went out and tested my tps. I used a pin in the back of the middle wire of the tps. To this I touched the red lead of my multimeter and I stuck my black lead onto the negative battery post and it showed 1.133 I loosened the two screws on the tps and moved it around and got the car to idle higher but not really lower. So I took it completely off the throttle body and the car did Idle a little lower but not much. So I shut the car off and turned the key to 'on' and tested the tps while it was off the throttle body and I got .70 Hmmm so the voltage goes low enough and I tested it through its range and it seems to work. I put a screwdriver in it while the car was running and turned it and sure enough the car idled higher and higher. Hmmmm... I messed with it some more on the car but with no success so I gave up and put it back on and put everything back together. Before I went back in the house defeated I started the car to make sure it was okay and now it was idling at about 2500. Yikes! It's way worse but I was thinking this is good because that definitely has something to do with my problem. So I'm thinking about the other guys post and how if it's above 1.1 it increases the idle. I'd like to get it below that but even when it was off and showing .70 it didn't idle down where it should. What else could it be? Hmmm...

I had cleaned the throttle body before but I didn't take it off the vehicle so I decide it wouldn't hurt to do so. So I take if off and as I'm cleaning the back side of it I'm trying to see if it isn't closing all the way. Well it is ....sort of. It's stopping on this little screw here against this plate but I do see a little bit of a gap over and under the butterfly valve. I figure that's normal. Then as I keep cleaning I can see that if I back this screw off a bit it will close the butterfly valve a little more giving it less air (which is what I think I need) AND at the same time it will take some of the turning pressure off of tps thereby lowering the voltage. Eureka! ...this sounds good! But why would it have been turned to begin with?

So I get it all cleaned up and put it back on. Start the car and it's a little better but still idling @ around 1500 which I didn't even know wasn't normal before to be honest. My complaint was the big surge on start up. Anyway, I'm making progress because it seems that the surge has gone away. Unfortunately thanks to you guys I now know that the idle is also way too high. So I figure I'll see if I can get the tps voltage down to .96 (read somewhere that that would be the best setting) So I hook up my multimeter to the tps and start backing out the idle screw (or at least that's what I'm calling it) counting turns in case this all goes bad. When my tps is showing .96 I stop, go over and fire up the truck and I could cry. Idles at 750. I don't think I've ever heard this truck idle that low. So that was it all along. I broke my brain on that. Why was it turned in though?

It's possible that someone was in there and turned it up before I purchased this vehicle in order to counteract the O ring issue. The first winter I had the truck you had to give it gas to keep it going in the cold. So they may have turned up the idle screw so it wouldn't stall instead of fixing it correctly. Then I bought the vehicle and replaced the intake O rings. Boom ...fast idle. Big headache for me but i couldn't be happier at this point. That took forever to figure out. Peace.