OK, some background first. It's my 03 Durango with a 4.7, 136k for miles and relatively trouble free. A month ago my wife had it and it overheated on her, the first time it's ever done this. Unfortunately she ran it hot for awhile, and after doing a compression check I traced the problem to a head / gasket problem. I found the drivers side head had a crack in it. No problem, picked up another head, put everything back together after changing things like the water pump, thermostat, PCV valve, belt, etc. The engine was surprisingly clean (carbon free), oil was clean and sludge free, and always ran good so I assume that there's nothing else mechanically wrong with it.

Started right up after the rebuild and it was idleing high (1200 in neutral). Finally coded out to a P0507 Idle High (duh!) with no other codes. I did the normal stuff - checked closely for vacuum leaks, missed hoses, etc. Made sure I didn't miss any intake manifold bolts, cleaned the throttle plate & made sure it was free moving, no cable hangups (the throttle cable is actually very slack which surprised me.) On a whim I changed out the TPS for a new one. Also took out & cleaned the Idle Air Control valve & housing where it's mounted. Went thru the computer reset procedure (battery disconnect, starter on, etc.) and then restarted the truck again, same problem. It starts and goes to 1200, sits there, and after I drive it for a bit idles in neutral at ~1500, in drive it's ~1100. Unplugging the IAC while running makes no change at all. Eventually it will code out with a P0507, but nothing else.

My next step is to pull off the intake manifold and see if I pinched one of the O-ring gaskets or something, but I would think that the idle would be inconsistent & there would be a stumbling soemwhere as it accelerated. I also sprayed carb cleaner around the intake with the engine running (as best as I could anyway) and had no change. the truck drives normally, shifts well, and has the same power although the gas mileage is down to 14.5 where it was normally 16. I attribute this to the high idle.

Valve timing was checked a dozen times over when assembling the engine so I'm *SURE* that it's correct. BTW, that was probably the most complicated and time consuming set of timing chains I've ever put on

Also, the battery is good (1 year old and just tested) and the alternator is outputting good under load (also confirmed by load testing).

Anybody have any other troubleshooting tips or ideas that they could pass on? I hate to start throwing sensors & parts at this....

Thanks!
Bob

 

I would tell you to replace the IAC?

 

Thanks, I was going that route next, after I double check the intake gaskets. Is there a way to test the IAC (resitance across leads, voltage at certain rpm, etc?) or do you just plop down the $70 and hope for the best?

What bothers me on it being a sensor / electronic problem is that there was no signs of any problems before the overheat problem. If all I did was remove / install the intake, how would it go bad?

Sounds like a Saturday job to me.....

Bob

 

I would try to clean the IAC if it's still in good condition. A little carb cleaner and a rag should do it. You can also clean out the hole the IAC attaches to. Just make sure no debris goes into the the intake. JMHO.

 

Thanks, did that already. I used carb cleaner & a rag / q-tips to get the carbon out, although it was surprisingly clean. Made no diffenernce at all.

Bob

 

To me if it made no difference I would seriously look into replacing it as that should have helped somewhat. You can always try a IAC out of a Junk Yard for a few bucks just to see if that is your issue without pouring money into it. Just clean it and make sure you don't push the plunger of the IAC in when cleaning.

 

OK, Monday was the day... it was raining out so I decided to work in the garage until I got this problem solved. Started with replacing the IAC with a new one. No difference at all. Convinced that it was an intake leak somewhere, I pulled the intake manifold once again (along with the fuel rails, AC, alternator, etc. to get to it) and was dissaponted to find that all of the gaskets where where they were supposed to be, nothing folded or pinched, all bolts tight. I took the opportunity to clean the intake manifold good, as well as the throttle body. Put it all back together and ..... same high idle problem.

At this point I went for the next solution.... cold Corona's.

I poked my head back under the hood looking for ANYTHING that could be amiss, and my eyes wandered across the power steering pump with two little wires poking out of a sensor. Hmmm.... why is there a sensor there, and why are those wires at an angle? Looking closer I saw that the sensor end was banged up & bent a little, most likely from me moving the pump out of the way during the rebuild. I pulled on the wires & half of the sensor came off with it. A quick trip to the auto parts store netted me a new sensor, an hour to put it in (but I'm getting damned good at putting on serpentine belts!) and....

SUCCESS!!!!

Started it up, idled high for a couple of seconds then dropped right down to the normal speed. Road test showed that everything is back to normal and my trusty old Durango is back to normal.

Apparently the PCM reads the switch / sensor and kicks the idle speed up when the steering wheel is turned. No sensor meant that it was always calling for raising the idle some. What that did with the IAC / TPS circuits are beyond me, but it all resulted in my Durango wanting to do 40 mph with my foot off the gas.

Never did get a code other than the "Idle is Higher than expected" one. Maybe there's no trap for that sensor?

Anyways, thanks for the help. I'm sure I'll be poking my head in here once in awhile to learn other things.

Bob

 

I knew the sensor was intertwined but didn't think of it. Thanks for getting back to us on this and taking the time to update your thread.

 

sweet, glad you got it figured out, and thanks for the update

 

Maybe there IS something to be said for cold beverages helping you fix a problem.....