Topic: rough idle, but engine is running fine with throttle

[mack90]

My jeep just started this very rough idle.  I have a good bit of vibration and a strange noise when idleing.  As soon as I touch the gas, everything is back to normal.  Any idea on what sensor this may be?  There is no engine light on.

[Jeffy]

I'd first check to make sure all of the vacuum lines are going to the right place.  What's it idling at?  I'd check for codes anyway.  Even if the light does not turn on it may have stored codes.  I'd be leaning towards a bad TPS, if I had to guess.

[mack90]

The  vacuum lines look ok.  This problem started intermitantly and is becoming more regular.  The idle is hard to describe.  There is little fluctuation in rpms (750ish), but I get vibration a deep almost rattle like noise.  I am going to clean the throttle body and check the resistance on the tps today.  Thanks for the help.

[jcsanders79]

O2 sensors and a burned out check engine light?

[mack90]

I am running tight on funds, but think it is the tps.  How do you check voltage on this while it is running?  Is it better to just check resistance with it unplugged?  What should the reading be?

[Bounty Hunter]

I'd remove all sensors, remove the TB, and give it a good bench cleaning.  Pay special close attention to cleaning the IAC housing, it's where the sensor with the plunger mounts.  This controls your idle.

[countryboy514]

its not a good check to check the TPS resistance. you have to check the voltage with the key on. back probe the connector with some straight pins with it still hooked up. its a three wire TPS, so its one 12V, one ground, and signal wire back to the PCM. signal voltage should be about 0.5-0.6 volts with throttle closed. and 4.8-4.9 volt at wide open. also check for a smooth voltage increase during a smooth throttle opening. BUT the TPS is not the only thing that would cause a rough idle. I would also check the O2 sensor with a scanner to see if it cycles voltage from 0.100-0.900 volts