2003 Sport Trac Rough/Pulsing Idle on Startup

[David V.]

My 2003 Sport Trac with 165k miles has recently started to pulse at idle on a cold start, with the pulses smoothing out with 30 seconds or so. Although the revs hold constant at ~1000rpm, it feels as if someone is pumping the gas. The problem is most pronounced if idling in gear (forward or reverse), though will also occur while in neutral.

Extra Notes:
The check engine is not on.
I tried replacing the IAC and have cleaned the MAF, but this hasn't seemed to help.

Has anyone else had similar issues or have any suggestions?

Thank you!

 

[crankyjew]

how long ago did you clean your MAF and IAC? I would recommend cleaning your throttle body as well as swshawaii suggested. That said, it took my truck a while after cleaning the intake components to "figure it out."

sounds to me like a fuel/air issue. check out your air filter, and consider replacing your fuel filter.

 

[Jermsy]

I know this is kinda basic but I'm mentioning it because I've effed it up before - When you changed out the IACV and the MAF Sensor did you have the battery disconnected? I fried the ECU on a nissan when I started out as a mechanic cause I was in too much of a hurry to disconnect the battery.

 

[TJ Sport]

Very common problem with the 4.0 liter is cam chain tensioner failure. First symptom is pulsing at idle, especially in gear. It's always worth pulling the valve covers on this engine, just to check the health of the tensioners. The left side tensioner and chain can be replaced in vehicle, the right side requires removing the engine.

 

[cz413]

Not sure if related to your problem but....

My '02 4.0 trembles at idle. It almost seems the idle is too low(600-700 I assume).

And just 2 minutes ago the truck shut off completely after doing a hard couple trembles at idle. This is the second time it's happened in a month. Last time I was stopped at a light.

The truck has had a history of losing power(not shutting off) while driving and very rarely shutting off while driving. Never a CEL. I don't notice any rattle sound.