Amateur mechanic here...

I have an 02 Dakota 4.7 90,000 miles on truck and 65,000 on the motor.

It started with a surging rpm issue from stalling to 1100 rpm's.

I replaced the TPS sensor and 1 O2 sensor (pcm read voltage issues with both) and it seemed the level out but it is now idling high 900-1200 rpms. However this is not all the time.. about 75% of the time it sticks at these rpms.

I calibrated the TPS as such:
Disconnect negative terminal
Turn and hold key for 20s
Remove key
Connect battery
Put key in on position
Slowly press and depress pedal
Start truck

Same story

I replaced my IAC valve and didn't seem to help much. But If you adjust the IAC you obviously get different rpms because it's open further or closed further. Why this is adjustable is beyond me. That may be an issue.

What is really getting to me though is if I tap the top of the throttle body lightly with a wrench, the rpms all a sudden drop to 600, every time! I cannot figure how this is happening.

I do have a multimeter and any suggestions of what anything should be I can test them.

Thank you

 

Could be a ground issue but more than likely its a cheap TPS and or IAC on this forum many have had problems with cheap sensors going bad within 1 year.


Always buy quality sensors not as cheap as they come OEM is the best but not cheap.


Have you removed the throttle body and cleaned it?

 

Could possible be a bad MAP sensor or a vacuum leak.

 

It's not adjustable. At the first key on the stepper motor will drive the IAC closed to reset the counter. After that the PCM can keep track of where the valve is.

A couple of things. Make sure the connectors for the TPS and IAC are clean and tight. After that, I agree with '98DakAZ. Replace the TPS with an OEM unit. As he says lots of parts are just crap nowadays.

Also, check for any vacuum leaks on the throttle body or the vacuum lines connected to it. Any leak can cause an erratic idle. Since it does kick down when you tap the throttle body this is a possible issue. You could also spray some carb cleaner around the base and fittings and watch for an RPM change.

You did remove the throttle body and clean all the IAC passages completely?

 

Yes the MAP sensor is overlooked and could be the problem the air temp sensor is another overlooked sensor. be aware that cheap sensors don't always show up as bad when tested they just don't function as they should.

 

I do apoligize, I forgot to mention I removed the throttle body and cleaned it out with the tb spray, I also cut 3 hoses due to small tares and cracks.
Same story

What does the tps run at to test it if it is crap..

 

No luck with the carb spray

 

I removed the IAT and the ohms climes after I pulled it out, as I researched it climbs as it gets colder

 

The TPS in the middle wire is reading sometimes at 45mV and other times 57mV it maxes out at around 243mV

 

The TPS is just a potentiometer. All it takes is one bad spot and it will be erratic - it may not generate a code.