My truck has been running real rough latley. In park the rpms surge all over the place when i put it in gear and tap the gas it almost stalls but only if i touch the gas. In gear with my foot on the break it idles fine. Ive cleaned the throttle body and replaced the IAC which worked for a couple days but now its back and worse. Im thinking its the TPS since it only sputters with my foot on the gas. Any help would be spectacular.

 

Maybe you got a bad IAC. That seems to be a super common issue. I've heard of soo many people replace them and have the new ones go bad in a few days it's not funny. Especially if you got it from a part store. I'd try exchanging that. Honestly this is a item I personally would only get from the dealer. I've heard of those being bad too but not nearly as many problems and they don't seem to be a ton more.


When my tps went bad it just surged at like going down the highway when I had the cruise control on is most when I noticed it.

 

Did you disconnect the neg. battery cable while you were installing the new IAC? Probably won't matter much as the computer should adjust regardless, but you never know. If you try it, it might run crappy at first but might clear up in a few miles.

 

Voltage sweep the TPS and MAP sensor, then get back to us.

 

everything you described sounds like a bad iac, EXCEPT the part about when you press the gas lightly it dies. the iac only comes into play when your foot is off the gas and the throttle plate is closed.

if the new IAC fixed it for a couple of days, and then broke again - thats not unusual for autozone brand or GP brand. i've gotten several bad ones from them. after wasting a lot of time on those, i only use SMP or Mopar brand. i've not gotten a bad SMP sensor yet.

if the new IAC didn't help, i'd go ahead with tps. its not overly expensive, about $40-50. new tps can help other problems, including excessive downshifting, throttle response, etc.

its a good idea to reset pcm with any new sensor type part. disconnect neg battery and turn key to start for 30 seconds.

 

Ive replaced the IAC twice. Duralast brand. Disconnected the negative batt cable each time and its been 200 miles since then.

Ill give you a more detailed discription of how the truck runs.
On start up. RPMS will hang high. and slowly lower. Then bounce up and down. Occasionaly truck will stall in park when i hear what i think is the fan cluch engadging. Put the truck in gear rpms fairly steady with foot on break. Heres where i get confused. When i take my foot off the break and tap the gas rpms drop to almost 0 and truck will almost stall. This only happens if i tap the gas. If i just take my foot off the gas and let the truck roll in gear it wont stall. When Crusing down the road. I Can feel the truck Shudder if i tap the gas.

Other thing to know is that the other day i was running out of gas and the truck would shutter really bad and ever since then the syntoms have been simmilar. The trucks been running rough before that however. Thanks for all the help guys

 

I'll say it again:

Voltage sweep the TPS and MAP sensor

This is easy to do and cost is zero. Stop throwing parts at it, as you'll only make your situation more confusing.

 

How do i test the sensors. What numbers should i be getting from them. I dont have the money to throw parts at it.

 

If someone would explain how to "voltage sweep the TPS and MAP sensors" Iwould appreciate it alot. Also what is an IAC?

 

To sweep the TPS, backprobe the signal wire (Orange & blue) with the DVOM pos (ground the negative lead) and slowly turn the throttle. Voltage should range from just above zero to just under 5.

For the MAP, you also backprobe the signal wire (Green & red), and slowly increase vacuum to the port while watching voltage. Same 0-5v range.

Both sensors have 3 wires. The other two are 5v reference and ground. Make sure you check those if the sensor readings are not within spec.