Rough Idle When at a Stop

I have a 2005 double cab with a V6-Auto with K&N AF that has approximately 90k miles. Generally, I love this truck. My biggest complaint is a rough idle (sound and a slight vibration) when I am at a stop, which is frequent in rush hour.

This is the situation. When the truck is in Park, the engine idles perfectly. No sound or vibration. When the truck is in Drive and I'm stopped, the engine idles roughly which includes sound and a slight vibration. The engine RPM is slightly lower than in Park (which I would expect). If I just barely press on the gas (while the other foot is on the brake) the rough idle disappears. When I begin moving the sound and vibration is usually present until about 15-20 mph. The rough idle occurs nearly 95% of the time, the other 5% is beautiful silence!

I know without seeing/hearing the idle in real life this is a stretch but would appreciate any ideas to start trouble shooting. Thanks!

 

hows the motor mounts?

 

I have 2012 Taco with a 6 and it has an interment rough idle while sitting at stoplights. Usually in drive at a light it idles at 600rpm. For no reason it will bump up to 850rpm and I notice the truck slightly vibrating. Sometimes it will lurch forward as if someone barely taped my rear bumper. I thought it was normal but now it's starting to bug me. After the holidays I'll bring it in to get it checked out.

 

motor mounts. but its present untill 15mph... weird.

 

When have the plugs been replaced?? I notice the same rough idle and pinging when I get gas from certain stations, I found a station that my truck likes and have been fueling there regularly.

 

Mine does that when the AC kicks in. Freakin hate it!

Both my 05 and 12 have done the same thing. This V6 is no smooth running engine for sure.

 

Same thing on my '12 sport v6. In park it is ok but slight vibration when stopped in drive. It has less than 3k miles.

 

I have a 2013 with 2800 miles that does exactly the same thing, was going to bring it up at my 5000 mi service

 

If the K&N Filter is lubricated I would guess a dirty MAF Sensor.

 

Ya, any of you guys clean your MAF or Throttle Body? Every spring I clean the TB, and MAF and install a new set of plugs. Always runs smooth, even when the AC kicks in..

 

my 2012 does it with 1,800 miles. a tad disconcerting but if they all do it and the trucks generally last forever it's no big deal to me. i mean, it could be a Chevy.

 

I had the same lurch in my 2011 DCLB. I was told that it was normal, I just got use to it. On my 2013 AC I don't have the same lurch.

 

Thanks for all the input. I've performed a cursory inspection of the motor mounts and didn't notice anything. I'm planning on cleaning the MAF and throttle body to see what happens.

Also, I have a new observation. I went to the open the hood when the motor was idling roughly so I put on the park brake and found out that the rough idle only happens when my foot is on the brake. No brake pedal + park brake equals no rough idle.

I'll keep this thread updated as I learn more.

 

Sounds like an issue with the vacuum brake booster...

 

This is out of my ignorance of the truck's systems, but could there be a leak in the brake booster's vacuum system which, in turn, causes the engine to stumble?

 

Vacuum leak or tight valve clearance.

 

I hadn't thought about the brake system. Is a leak in the brake vacuum system something that I could diagnose at home or something better handled by a shop? Anything particular to look for?

 

If there was a leak in the vacuum booster, your pedal would most likely get rock hard and you would most likely have a CEL with lean codes.

 

Mine does that when it's still warming up and sometimes at stop lights since almost new...never got around to figuring out what it was

 

Mine seems to do it when the temperature drops outside. I never considered it a problem.