02 explorer code P1506, manufacturer controlled idle speed

[jj48chris]

I am getting a P1506 code ( manufacturer contolled vehicle speed, idle control, auxilary inputs ) I replaced the idle air control valve, but it did not solve the problem. the vehicle idles at 1500 rpm in park, 1100 in gear. anyone have an idea on what the problem is?

[Biker920]

Originally Posted by jj48chris

I am getting a P1506 code ( manufacturer contolled vehicle speed, idle control, auxilary inputs ) I replaced the idle air control valve, but it did not solve the problem. the vehicle idles at 1500 rpm in park, 1100 in gear. anyone have an idea on what the problem is?

try checking tps(throttle position sensor)& MAF sensor also check any throttle linkages for binding&sticking. good luck

[shorod]

Per the factory service manual, that code is defined as "Idle Air Control (IAC) overspeed Error and is set when the PCM detects engine idle speed that is greater than the desired engine idle speed. The FSM lists the following as possible causes:

• IAC circuit short to ground
• Damaged IAC valve
• IAC valve stuck open
• Vacuum leaks
• Failed EVAP system
• Damaged PCM

Did you by chance have any other codes that you didn't mention here? Have you tried unplugging the IAC to see if that makes a difference in idle speed? If not, then you might want to remove the IAC again and spray out the IAC passages in the throttle body. I've been very pleased with the aggressiveness of STP Throttle Body Cleaner spray. It seems to cut through the throttle body grime better than many of the carb and choke cleaners.

If the IAC passages are clean and the throttle body is also clean, then you should check for vacuum leaks as those have been pretty common on V6 Explorers over the years.

-Rod

[jj48chris]

I have cleaned ot the throttle body and the aic passages with no change. I adjusted the throttle linkage, worked great for about 5 minutes, then back to the high idle. i unplugged the aic and there was no change in the idle when i unplugged it. i drove the vehicle about 40 miles and the service light came back on. now with 2 codes, P1506 and P1504, both with the same definition.....manufacturer controlled vehicle speed, idle control, auxilary inputs......any tips on where to go now? also, i did check for vacuum leaks and found none

[shorod]

The P1504 code means "Idle Air Control (IAC) Circuit Malfunction." This most likely was set when the engine was running with the IAC unplugged since one of the possible causes for this code is "IAC circuit open."

Since unplugging the IAC made no change in engine idle speed, I'd suspect that you either have a wiring issue to the IAC (not really likely since the code P1504 appeared when you unplugged the IAC) or you have another bum IAC. You could also try turning on the A/C, Defrost, or momentarily holding the steering wheel against one of the steering stops. If the IAC is working properly, any of these checks should result in no appreciable drop in engine speed under the increased load on the engine. If the engine speed drops while the compressor is engaged or the steering at a stop, the IAC is not doing its job.

-Rod

[jj48chris]

ok, i replaced the iac again and the throttle position sensor, now the idle is up above 2000 rpms in park......need ideas of what else it could possibly be.

[shorod]

What does the idle speed drop to when in Drive with the brake applied? Have you cleared the codes recently and checked for new codes? How smooth is the idle in park and in gear? Have you checked for vacuum leaks?

-Rod

[jj48chris]

the idle speed drops to about 1300 rpms in drive at a dead stop, then when i go back to park, it jumps to 2500 rpms then back to around 2000. I cleared the old p1506 code, no new codes yet, but haven't driven a lot yet. I did check for vacuum leaks but didn't find anything. the idle is smooth, just high. seems strange that it gets worse with new parts.

[shorod]

From the service manual it looks like the 2002 still uses a throttle cable rather than incorporating the throttle by wire system. Check the throttle cable to make sure it is not binding or snug. With no pressure on the accelerator pedal, there should be some play in the throttle cable at the throttle body.

You could also pull the intake air tube from the throttle body and verify that the throttle plate is closing all the way. There could be some carbon build up on the back side of the throttle plate or in the throttle body that is preventing the throttle plate from closing all the way.

-Rod

[jj48chris]

Thanks Rod, I think it's finally fixed. the throttle cable was binding behind the gas pedal, i think i got it fixed, but if it starts up again i am going to replace the cable. I did loosen it once before, but not at the gas pedal. Thanks again for all your help, Chris