Yesterday while I was warming up my truck the idle on my truck went down to 2 on the tachometer so I hit the gas and it went back up to 6 on the tachometer thats what its on all the time.Then after a few minutes it went back down to number 2 on the tach .I again hit the gas but this time the idle went to high all the way up to 11 on the tach.It was pretty cold here yesterday about 30 deg outside.But it did this a few times during the summer when it was 85 out.what could be causing this?theres no check engine light on at all.anyone?

 

You could be losing fuel pressure so it should be checked. I bet it's IAC valve though. Those things can be a pain to diagnose and cause funky idle issues often times without throwing codes. I've never had one act funny on my Dodge yet but a couple 5.0 Fords I've had needed a new one.

 

+1 for IAC, mine only acts up when it's cold out. tried to clean it and it ran good for about a day. Would suggest outright replacing it.

 

Could be a tps to. I had to replace iac and tps to fix my surging

 

Try to clean the iac motor on back of throttle body. My done that

 

i have the same issue with my 1998 2500 but its every day no matter if its cold or hot or im driving and it just bogs down and back fires. i have to slam on the gas to make it run right again. ..... im no master mechanic or anything i can hold my own but what is "IAC, and TPS" and where are those on the truck. and just real stupid question this wouldn't affect my gas gauge not working would it? thanks everyone

 

IAC = Idle air control motor. On the back side of the throttle body. Four wire electrical connector.

TPS = Throttle Position Sensor. Drivers side of throttle body. Three wire connector.

In your case, I would check TPS first. And no, neither of those will affect your gas gauge.

 

If you have this problem with gauges not working, I would say look into a bad electrical ground. I have a pet peve with throwing parts at something without reading codes first. I would check fuses first, then fuel pressure, then see if your cat is clogged - threads on that in this forum too. Fouled plugs or old plug wires can cause it too. I had this issue once on a gen 1 ram after I hit a dip in the road really hard, found out it was running on 4 cylinders and the fix was the coil wire, it was detatched under the boot so it looked like it was on, but was really off. Pushed it back on & all was well, but hard to tell at first. A carbon build up in the EGR can cause it sometimes, but that is rare. So, read the codes & see what pops up and let us know what you find. More over, if a sensor is implicated, first check the connection on it before buying a new one, because sometimes it is just as simple as cleaning a connection or pushing a connecter all the way on again.

 

OK, i have changed out the TPS, AND THE IAC, and im still having this idle issue.... if i had long hair i would be pulling it out..... people keep telling me vacuum leak but there's 150 damn vacuum lines im getting ready to just light the damn thing on fire.... i'v done a tune up (everything is fine there) changed these 2 sensors im running out of ideas......

 

Vacuum leak would have it idling high. (if it were an external leak) Check your fuel pressure.