corrected vaccum leak. Still high idle and obd2 code 1506???

 

Did you dis-connect the battery?

 

yes then idled for 15 minutes, then drove around for 15 minutes. still high idle

 

If you are sure that ALL vacuum leaks have been corrected, then:

What year? What engine?

 

1988 f150 4x4 402 ltr 5 spd std. After test drive, the only code I get is 1506

 

1988 shouldn't have a PCM.
1998? shouldn't be in this forum.
Maybe 2008? IIRC, didn't have a 4.2.

 

Duh....sorry.....1997 f150 4.2 ltr 4x4 5 spd. "High idle" Vaccum leak repaired. Battery disconnected for 5 minutes. Idled for 20 minutes and driven 10 miles. Still high idle. The vaccum leak was located behind the plenum at the PCV elbow ....replaced both peices.

 

Maybe you can get an Admin to move this to the proper forum?

Do you still have the P1506 code?

More than likely you still have another significant vacuum leak.
Check the PCV valve and its hoses for a vacuum leak.
And check that the EVAP Canister Purge Valve isn't stuck open.
And check that the EVAP CPV diaphram will hold a vacuum.

With the engine idling, disconnect the IAC valve and see if the RPMs drop.

 

Done.

Moved to the '97 - '03 F150 forum.

Stewart

 

Do this next.
With engine at hot idle, remove the IAC electrical connector.
Does the engine drop in RPM?
If no, the IAC is stuck open or there is still an air leak past the throttle plate at some point.
Normal hot idle is 650 +/- 50 rpm.
Idle outside this limit set the 1506 code.
Without the IAC it should drop to about 500 rpm that is normal for this test.
If you clear the problem,
the better way is to remove battery on a cold engine to clear and reboot.
Then start engine to see that cold high idle does occurr normally then comes down to 650 as the engine full heats. Do this with the lights on and fan on high.
After full warm up, drive about 5 miles, then do several hot starts.
After this procedure the engine should have perfect starting under all conditions unless there is still an issue.
Good luck.

 

Repaired! Found vaccum leak at PCV elbow. Clean IAC but still a problem. Replaed IAC and is now OK! Thanks for the help!!!

 

I am having this same issue on a 2001 Sporttrak. 1506. Changed IAC with one that mounts 180 degrees off than the original which is a tad strange. I am at the limits of the cabling. Hot idle at 900. Cold idle 1200 approx.

One note, its not the original engine in the vehicle but it was installed by a competent overworked mechanic. I found some thing loose, like the mass airflow unit not bolted to the filter box tightly, loose heater vacuum line , a nicked plug wire which was causing a miss during bad weather, but none of this has fixed the idle. yes I reset the battery a ton of times. Unhooking the negative or positive is a mystery to me for a reset, but I did both.

 

I'm also having the same problem. 2002 F150 4.2L V6 w/manual transmission.... likes to idle at around 1000-1100 rpms.

I had lean codes P0171 and P0174. I cleaned the MAF and throttle body, replaced the fuel filter, and replaced the two forward O2 sensors, then erased the codes.

Now after driving about 200 miles, I have P1131 and P1151 codes. (also lean)
Erased the codes and drove other 200 miles... same thing.

I have tried to eliminate all possibilities of a vacuum leak, and I'm starting to believe this has NOTHING to do with a vacuum leak, but instead that it might be the ECM trying to compensate for a "perceived" lean condition by feeding fuel to the cylinders which is speeding up the engine, because on Closed Loop, the Short Fuel Trim is always up at 32.8% at low RPMs and at idle. It also seems to rev up a little when I push the clutch in. Unplugging the IAC makes absolutely no difference in the idle speed. It does seem to reduce the amount of revving when I push the clutch in.

When I reset the codes and the engine is running on OL-Fault... the engine runs great.... and when I push the clutch in while driving, there is no revving. When I park, the idle is lower... 780-920. But when I take it for a longer drive and it switches over to CL (closed loop) all the problems come back.

Any ideas? Are our problems related to the same issue?

 

A 4 cycle engine only responds to airflow.
This is how and why your foot can accelerate the engine.
You must find if the IAC is being held open or there is an air leak from some point you missed.
Added gas, does not RPM with out air. PCM will not either unless it opens the IAC. This is how cold start high idle is done.
4.2L motors have a particular issue that often is different than a V8 when standard transmissions is involved.
Look under the intake manifold for vac hose you may have missed.
Good luck.

 

Low RPMs and light load is when a small vacuum leak has the most effect.

Is the EGR valve fully seated? Heck, the vacuum leak could be in the HVAC system.