Hello all. I have a 99 dodge ram 1500 2wd 5.9 with a weird high idle problem. It has ran fine until yerterday. I put gas into the tank and my gauge was showing half a tank. I took it home and parked it. I went out to start it later that night and it would not run unless i was holding the gas pedel down a little bit, when i would let go of the gas pedal the engine would die. I have already replaced this past year the following:
IACV
MAP
Fuel Pump

I did repalcing the IACV again yesterday under warrenty and now it is running but with a very high idle "1600 rpm". I did notice that the IACV is not moving at all during key up and during engine running. I tested the wiring connector at the IAVC and there is no power. I checked the connector to the pcm connector and all wiring has continuity through them. I did notice that also now my gas gauge is show it to be a full tank. I am thinking it is my PCM? Any ideas. Thanks.

Also i did reset my PCM already and it had no effect. Thanks again.

 

sounds like a tps problem advance has em for 40 dollars i think it a throttle positioning sensor

 

Wonder if you got a bad IAC motor.... Key on, engine idling, there should be 12 volts on two wires. other two are grounds, and may or may not be grounded at a stable idle. (the PCM will ground both wires to lock the IAC in place.)

 

I replaced the IAC again today and it did not help. Any idea on what of the 4 wires to the IAC should have power and how much? thanks.

 

vac leak or bad coolant temp SENSOR not sender .the sender has 1 wire the sensor has 2 both located at the front of the intake

 

ok replaced the TPS and it did not changing anything. on the IAC connector i am getting the following voltage with the truck running:
1= gy/rd wire: 3.5 volts
2= yl/bk wire: 7.1 volts
3= br/wt wire: moves from .8 to .3 volts
4= vt/bk wire: moves from .6 to .1 volts

The engine starts at 1500 rpm and if i gas it up it will move up to 2000 rpm and stay there.
Any ideas?
Thanks.

 

Ok, seems the system is weirder than I thought. All four of those wires go to the pcm, and the pcm can apply 12 volts, or ground, to any of them..... still, you are getting some rather low numbers for voltage there. Check the pins, and make sure they are clean, and tight, at the pcm end.

According to popular theory, when the battery is disconnected for a while, the PCM will 'forget" where the IAC motor was, so, it will drive it all the way in, the next time you turn the key on. Might wanna try that as an experiment..... Disconnect the battery for a few minutes, then have someone else turn the key on (but, don't start the motor.....) while you watch and see if the IAC does indeed close. (it might back off a bit after it seats all the way in. )

 

If you do decide to try the coolant temp sensor, there is only one on a 99. It does double duty , pcm signal/gauge signal.

 

How long has it been since you have removed and cleaned the TB? Did you clen the IAC port when you installed the new sensor? If the answer is no to either of the above questions, remove and throughly clean the TB especially the IAC port. Disconnect the negative terminal for about 1-2 minutes.

After you reinstall the TB with a new gasket, reconnect the battery, start the engine and let it idle, DO NOT REV THE ENGINE, and let it come up to operating temp while idling. Switch it off, restart and go for a drive making as many starts and stops as possible, such as stop signs. This gives the PCM a chance to relearn the part throttle settings. After doing all this, your idle should be at 650-700 rpms.

 

I removed the TB yesterday and cleaned it out really good. I reset the computer "I Left the battery unhooked until this morning" tried it and it still is giving my a high idle. What is the minimum amount of volts to operate the IAC. Its almost like the IAC is getting the volts to open it but not enough to close it to bring the idle down.