NEED HELP P1506 IAC overspeed.

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Randy Bobandy

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I drive a 2001 Lincoln LS 3.9L V8. I was getting this code (p1506) along with another code (p1504). I have replaced my IAC, then I discovered I wasn't getting any voltage to the IAC. I've restored the power to the IAC and am now just receiving the one code for IAC overspeed. Is it possible that this new IAC could be sticking, when it's only a few months old, and hasn't even been working (due to the lack of power to it)?

I'm planning to get a can of carb cleaner tomorrow, and spray it around the throttle body while the engine is running, to check for air leaks. Can someone help me locate possible points of interest, to look at for leaks?Also, is there other issues that could cause thic code?

Thank you for your time.
 
When they stick, it is usually closed (under speed).

So, if you unplug the IAC electrical connector while the engine is running, does it slow down or stall?

You didn't play around with the throttle hard stop adjustment while the IAC wasn't working did you? (How did you keep it running with the IAC not working?)
 
I had had the car in texas for months (where I didn't have to run the codes. Honestly didn't notice anything wrong. Well I ran the codes when i moved and I found out about these problems. I put on a new IAC and the codes never went away, but the car ran normally. Today I finally got the voltage to it, and it runs noticeably different, but a much higher idle (around 1,200-1,400rpms. While in park if I tap the accelerator the rpm's will jump up to almost 2,000 and they come down either very slowly, or not at all for a little bit.

If i unplug the electrical connector the engine speed slows, but doesn't stall.

I didn't make any adjustments to the IAC. Took it from the box and put it right on the car. I don't know what the throttle hard stop adjustment is.
 
I'm wondering if it's likely that the person who owned this before me made some funky adjustment to the throttle to keep the car running without the IAC functioning. So now that it's working the idle is just way too high, but that doesn't explain why the idle seems to stick.
 
So, it's possible that the previous owner messed with the throttle hard stop to hide this problem from you when he sold it...
 
Yes, that isn't unlikely. could you tell me how and where to check this component? What could be causing the rpms to remain so high after I accelerate?
 
I'm going to assume that PO adjusted the hard stop to keep the throttle too open, so that it wouldn't stall. The book doesn't say how to correctly adjust it, it just says not to.

If I had to do it, I would disconnect the IAC and back the stop screw out until the engine (fully warmed up) was close to stalling. After that, reconnect the IAC. If you still have problems, you may have to disconnect the battery for five minutes.
 
He's also throttle by cable, may want to check that see if it's able to move freely, on a shot of fuel see if it's restricted on coming back down or something. Wouldn't be the first time someone caused a kink in a cable or clip gummed up. Just thinking out loud here.
 
I did what you recommended, Joe. This brought down my idle to around 700rpms. I also checked the throttle cable and there was some slack. It seems that when I lowered the idle, it added removed some of the slack in the throttle. Now, after I step on the gas the idle gradually returns to the normal 700rpm's. I'll be going for a test drive in a little bit once my wife is done shopping, but this may have fixed the problem. Thank you both for the help. Especially you Joe. Not sure if you realized, but you coached me on the wiring to this IAC in another thread.
 
Alright so I stopped at autozone to clear the codes, hopefully for the last time, and P1504 had come back. That must be because i disconnected the IAC while the car was running to adjust the idle, right?
 
Randy Bobandy said:
Alright so I stopped at autozone to clear the codes, hopefully for the last time, and P1504 had come back. That must be because i disconnected the IAC while the car was running to adjust the idle, right?
Click to expand...

Yes, most likely.
I'm glad you have this resolved. (I guess we can't be sure it is adjusted correctly until your next cold start...)
 
Randy Bobandy said:
... How many miles does it take for the computer to read everything?
Click to expand...

For "everything" it's a bit more complicated than just miles. Some of the diagnostics require particular conditions to be satisfied, such as a particular fuel tank level. There are some drive procedures that you can follow if you need to set all the monitors as quickly as possible. Otherwise, it make take until you have used up a tank or two of gasoline.

For the IAC codes, I would think those would come back on the next trip, if there is still a problem there.
 
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