Code 48 Advise Please!

[tlry00]

So my 94 3.9 keeps throwing a 48 code
* I've cleaned & swapped the idle air control motor (Stepper motor)
* Cleaned the intake
* Put new air lines on the lead to the stepper
* Reset base idle several times
* Cleaned up the speed sensor
* Did continuity tests 15, 16, 25 all passed (Test 25 I'm not 100% sure I did correct)

I'll clear the code and drive the truck... it will run great, then after driving at least 5 minutes and pull to a stop (either parking or stop sign/light) it will idle very rough then smoothes out as the 'Check Engine' appears

ANY THOUGHTS? Help is greatly appreciated

[OkieRover]

I expect you've seen this from Robison....
Code 48 - Stepper motor

1. Check base idle speed as follows: First remove and clean the idle motor and the port it screws into. Clean the throttle body as well.
2. On the top of the throttle body you will see a hole (possibly covered by an anti tamper plug) for the base idle adjuster.
3. Remove the air bypass hose from the throttle body, which will cause the engine to speed up to 2500rpm or so. Unplug the connector to the idle motor after 5 seconds then reconnect the hose.
4. Squeeze the hose shut with needle nose vise grips and adjust the base idle using an allen wrench to give an idle speed of 6-700rpm. Get the lowest speed you can that gives smooth running and does not stall when blipping the throttle. Screw in for slower idle, out for faster idle.
5. Reconnect the idle stepper and remove the vise grip and you should be done.
6. In addition, refer to tests 15 and 16 of continuity test procedure. Check road speed sensor- refer to test 25 of continuity test procedure.

Other than that I haven't seen this one, sorry.

[tlry00]

Yeah! I've done all that several times... I'll try again

Any other suggestions, I'll try even the most elementary (maybe I skipped something)

[tlry00]

Anyone else?

[92RRRANDALL]

First of all I will tell you that contrary to postings on the web that stepper motors made for other systems are the same as the one on the RRC are the same is incorrect. They are not the same, and you can easily confirm this with a multimeter and by direct substitutions while observing idle quality.

You may have a problem with the road speed sensor. If the RSS is not sending a pulse(vehicle is moving), then the idle control system is turned on(vehicle is not moving). I think it's unlikely that the RSS is the fault, but that is what turns the idle system on and off, so check it thoroughly.

The code 48 may also mean that your engine is faulty and now the stepper cannot do it's job correctly. That could be cause by using the wrong spark plugs, wrong cap and rotor, etc. That may also be caused by the air gap in the distributor being incorrect. That may also be caused by a dozen small faults in your engine which are conspiring to produce a poor idle. Idling is when most minor faults manifest themselves.

Randall