1996 2.3L P1506, Need Help!

[frederickm86]

I have a 1996 2.3L. I was originally pulling codes for Insufficent EGR flow as well as Ignition Circuit 1 & 2. After putting in close to $1000 into this truck I am currently pulling P1506 Idle Air Control Overspeed. The truck is no longer pulling the previous codes (EGR & Ignition). The truck idles at 1100 when started. While you are driving idle seems normal. When you stop or engage clutch idle runs anywhere from 1500-2000. Add the heater running and that number increases by 500-600. There are numerous threads relating to this issue but here is what I've replaced in the last two months.

EGR valve
DPFE
PCV valve
Full tuneup(plugs, wires, all filters, etc.)
IAC (x3 thinking I've recieved defective units)
TPS
Oil Pressure Switch
Coolant Temp Sensor
Temperature Sending Unit
Radiator (unrelated)
Thermostat (unrelated)
Belt Tensioner (unrelated)
Clutch, rear main seal, & slave cylinder (obviously not related)
Brakes all around (also unrelated)

I've checked for vacuum leaks, there are none that I can find. I'm thinking the only things left to replace are MAF sensor, EVAP system (I've heard that can indirectly cause this problem), or the PCM itself. I really desperately need some help. My registration has expired and the truck will not pass inspection with this issue and no renewing registration without inspection. I've put almost the value of the vehicle into repairs but it's too late to regret it now. If anyone has had a similar problem I am open to any and all suggestions. I've also gone as far as putting on the old IAC to see if that made a difference but it did not. After resetting pcm this code comes back anywhere from next startup to 30-40 miles down the road. Thank you in advance for any help or ideas.

 

[JC 97]

according to chilton manual, the throttle body or throttle plate is contaminated or very dirty.Try some seafoam or visually check the throttle plate to see if it is indeed really dirty.It also lists the evap system.

 

[Thed]

This code just popped up for me too but I just got done cleaning out the entire intake. I already replaced the IAC valve and the PCV valve. All my vacuum lines seem to be in perfect working order.

Could it be the TB spacer I just installed???

 

[killj0y]

like previously mentioned maybe cleaning out some of the vacuum system and throttle body/plate? Have you recently changed out your air filter? Check for vacuum leaks again? Maybe smoke out the vacuum system to be sure...

 

[fivestring]

Make sure the idle stop screw isn't turned in too far, not allowing the throttle plate to close completely.
Disconnect battery to clear computer.

I would look inside the throttle body to see where the IAC plunger seats to make sure, like the other guys said, it is clean first of all, then look for any burrs or obstructions.

Then I would look up the specs on what voltages the IAC should be receiving from the ECM. backprobe the IAC connector and measure those readings on a meter and that should tell you if the IAC is getting the correct voltages at the proper times from the ECM.

The 500-600 rpm increase with heat on is probably the same as turning on the A/C. the ECM will boost idle a few hundred rpms to compensate for A/C compressor drag on the motor. I think the A/C compressor activates with the heat system as well.

 

[tomw]

If you have enough carbon and crud build up on the throttle plate, or the interior of the intake manifold where the throttle plate is mounted, it could interfere with the throttle completely closing. Worn throttle plate bushings could also cause the throttle plate to bind and fail to close completely. They could also allow air to leak past the throttle plate shaft, enabling a higher idle speed.
I would remove the intake air ductwork, and inspect the throttle plate and surrounding intake manifold pieces for crud and stuff. I think with it apart that far, I would also take some O2 safe cleaner and hose down the intake manifold interior walls. Be careful of blowback if you use a spray cleaner.
I would also check the throttle plate bushings by trying to move the throttle plate around using one hand, while holding it from springing closed using the other hand on the external plate linkage. If it can be moved in any direction, it is loose, and should be investigated further. They are supposed to rotate, but not wobble.
tom

 

[98singlecab]

code 1506

my 98 ranger is having the same issue. it's a 2.5l 5spd with 161k miles and a/c. things i have done so far are.
replace IAC
replace TPS
clean MAF
cleaned throttle body
backed out idle screw so it's barely touching the throttle plate
smoked intake, no leaks in vacuum system.

my truck stays at a higher idle when I come to a stop foot on clutch and coasting in. once I'm stopped it idles down.
I'd like to make my exhaust a little louder but am waiting till I get the idle thing fixed before I do that.

what have you guys done to fix your rigs???

 

[98singlecab]

code 1506

ok so this is what i've discovered. the IAC I got from o'rielly's was a BWD it had a socket in the back that fit a square drive. I finally decided to try and turn it. It turns and my idle adjusted accordingly. so now when i let off the gas my idle goes back to where it should be quickly. been driving it for a week now and no more high idle when I let off.
so for now I think i've fixed it.
I hope this helps any future people searching