Hey guys. First I have searched threads and found lots of info that lead me to this point, but not finding a definitive answer, so posting in hopes someone has an answer, or can point me to a thread with it. I don't mind reading if something exists already for what I need

Details - 2000 Dodge Ram 1500 ST 4x4 5.2L Reg Cab 148,000 miles (bought as a cheap beater/bug out truck)

p0505 code. Idle is a bit high @ 1200rpm or so, and surges here and there with the truck just sitting. Surges more if I shift through the gears, but most noticeable is when I turn the A/C off, like if I let it run for 30 seconds or so, and turn off, idle will sometimes jump up to 1500rpm or so, then drop back down. I have seen the rpm's go to about 800-900 but the needle bounces a lot in this range.

Replaced IAC valve/motor because I don't know the history on the truck, only that it's in very rough shape and needs a lot of work that I am currently doing. Also cleaned out the throttle body and IAC port before installing new part.

Tested TPS with ignition on, manually moving things with my hand. I get truck voltage at 3rd wire, ground at 1st wire, and closed voltage reads .89v constant, moving it with my hand the voltage climbs and descends as expected with no noticeable spikes or drops.

Tested the IAC connector with it unplugged and ignition on and if the picture loads this is what it looks like (truck not running, only ignition ON). Also to note that I tested this connector with a snap on test light. Numbers 1, 2, and 4 all flash the test light with truck running, but #3 (the one reading 6.89v) barely lit the test light, just a very faint green light that I had to look very hard to see, and it was not flashing, just a constant faint almost non-existent light.

I am trying to diagnose a possible bad PCM because I am throwing a lot of money into this truck and all I want to do is get it on the road and have it some what reliable as it will eventually turn into my daily driver when I find a job.

 

Check connections at the PCM. They like to corrode, and then things start getting strange.

 

idle problems are usually either IAC or TPS.

<< if no change - keep your old ones as spares. >>

if you already replaced IAC with no change, i'd try the TPS next.
i've had surging idle problems before that were fixed by new tps.

 

Thank you for the replies. I checked the PCM connectors and there appears to be no corrosion or dirt or anything, just shiny terminals and pins.

I checked the TPS with the screwdriver handle method. When I tap the TPS gently in different areas the voltage goes from .82v to .83v for a split second, then back to .82v. Not sure how dramatic of a change it's supposed to be, but that is the result.

Going to try replacing the TPS today I guess if the weather holds up, see how that goes.

Now I have another question, when looking at the throttle body I noticed a zip tie around the piece that the throttle cable connects to. It is acting as a bumper against the Idle screw (I know not to adjust this screw). Just curious why there is a zip tie there, maybe to keep the metal from clanking everytime you release the pedal? or did someone add this at some point to increase the idle? I don't want to remove it because I have seen this on other vehicles before during my life as a tech, but I never paid any attention to them. So anyone with a 5.2, do you have a zip tie like this?

 

Remove the zip tie and disconnect the negative battery cable before cleaning or replacing any sensors. This will allow the PCM to relearn the new or cleaned part.

 

damn dbl post.

 

ok, replaced TPS, still have p0505 the second I start the truck up, and idle did not change much. Then I removed the zip tie. Good news is the truck now idles at what I think is reasonable (see picture). It is a little rough, but still better than my 01 2500 v10 was.

Guess it is back to diagnosing the PCM and the one wire going to the IAC that is not flashing the test light.

 

Yep, that's pretty close at the very least.

If you clear the code, does it still come back after removing the zip tie?

 

@HeyYou , yes the code comes back the moment I start the truck, as long as it takes me to select 'read codes' on the cheapy mac tools code reader. Same thing if I disconnect the battery for a while too.

editing to add a more precise answer- if i clear the codes and start the truck without turning the key off, the code stays gone. But as soon as I turn the key off, and back to IGN On, the code is there again.

 

well, I pulled off the throttle body today, soaked it down with CRC Air Intake cleaner, it was filthier than I imagined. I thought I cleaned it good the other day, but glad I decided to take it off. Also replaced all spark plugs, they were terrible, all white and yellow, I don't know how the truck was running. One of the metal heat shields was compressed around a plug so I had to soak that over night and spend a couple hours today getting that things off just to get to the spark plug. But thats all done.

Now the truck runs, revs like it should, etc.. but one time I revved it up with a quick tap and let my foot immediately off the pedal, and the engine died. Started right back up though no problem. Still have my code p0505 and rough/bouncy idle even though it is in a good range right now. Still concerned about not getting one of the wires on the IAC to flash like it supposed to. Traced the wires from the IAC all the way to the PCM, seperated those 4 wires from the rest of the bundle checking for problems, shorts, breaks, etc.. even ran a resistance check from the pcm connectors to the IAC connector and they are all in the same range.

So I think I am about ready to just order a PCM on Monday. This place I am looking at online has it for half the price of anyone else, rebuilds them there, and programs them to the VIN before it's shipped out. I don't have to send mine to them until I get their's, and it's postage paid. Will post more updates if any come about.