Hello, I am new to this forum. Would like to say that all of you that post to this forum have been a wealth of good information. I also have a problem that is stumping me good. 1999 QC sport 5.9 auto trans that seems to run good in open loop but as soon as it goes to closed loop the iac opens and the motor wants to stall. Now no codes pop up. During accelertion it stumbles but then seems to smooth out. changed coolant and tps sensors but no help. Have cat guted. Wondering if o2 might be my downfall. Any input would be great.

 

that is a good question BLUERAM....i have a similiar situation (and same truck) that when i start the truck cold i can hear the iac close and then after about a minute it opens and makes the truck run rough and there is a huge sucking sound, i tap the throttle and the suck sound stops but then starts again for about a minute then goes away. I found last night that i also hear the sucking sound when i get on it and it is about 2600 rpms and up.....plenum gasket has been changed, full tune up, iac was changed, tps, secondary o2 sensor.....

any ideas anyone.....i figured i would piggy back on your initial post b/c they are about the same.....only issue i have been finding is that there really isn't alot of info here on iac hissing or sucking sound...either very few have the issue of no one know what the fix is...hope someone does.....

thanks

mavrik

 

hey, welcome to DF!!! i would take the IAC out and clean it and or get a new one. i just cleaned mine and it started working alittle better but sometimes it still idles alittle low and rough. you could also try the o2 sensors

 

will the 02 sensor effect the iac? if so the front or rear 02?

 

i dont know how much it would affect it but i would make you engine seam to run rough and run really rich so it might not be idling good. its the front O2 sensor that would go bad, the rear only tells if the cat is bad. im suprised you dont have the CEL on though if its the O2

 

The o2 doesn't always set a CEL...at least not right away. I have a bad one in my car (which I verified via the PowrTuner), but I have no codes set as of yet.

The rear o2 does have some effect on your fueling, but they don't go bad too often.

I would do what has been suggested though. Clean/replace the IAC. Clean/replace the o2 sensor.

 

Thank You, Tani. I took the iac out and did the cleaning but no change. Trying to get forward o2 out but they don't give much room to get o2 socket in there. Did find a small cut in the black wire of the four to o2. Getting dark and bugs are bad. No room in my barn at the moment to get blue in. Wonder if there is slight corrosion in the wire to throw wrong signal. Have new o2 coming tomorrow. What suggestions does everyone have on a catback for ram. I had flowmaster 50 series DOR but was not happy with the sound (to mellow). Michigan salt destroyed it in 3 yrs. Mavrik, Sorry to here you are having the same problems. Let me know when you find out what the cause is. This is stumping the heck out of me. I keep hooking the otc machine to my truck and it just will not spit out any code or pending ones.

 

Will do....good luck on your end and let me know what you figure out....

 

my truck does that when its cold too.. i think they all do its the choke.. runs rough then revs up a bit and settles down.. mine does it 2 or 3 times before its warmed up.. and makes that air sound.. i think its air being sucked threw the throttle body openings.. since its reving up higher without the flaps opening up its sucking air threw the little opening between the flaps and throttle body

 

Mavrik, Well i started my truck after a few days and i got the engine light on. So now i have to get the machine plugged in and find out what the mystery is. My luck it won't be that easy. lol lol. I will fill in info tomorrow, i hope. Oh one more thing, this time on start up i did not notice the iac sucking sound unlike previous. We will see. lol