Rough Idle

I realize that there are plenty of threads discussing rough idle on the 2.7 4 cylinder. This one might be new. My 2.7 runs perfect and idles like a new Rolls Royce when the weather is warm. As in summer when it's up around 70+ degrees or higher. However, once the weather turns cold it idles rough. Not the kind of "rolling smooth type rough idle" we all experience with the 4's but a "jittery" kind of idle.

Checking the plugs recently had no effect. Octane has no effect as far as fuel or octane rating is concerned. Changing over to 91 octane ethanol free from 87 ethanol or 91 octane ethanol free made no difference. Runs the same with 87 octane regular with ethanol. Ambient temperature seems to be the culprit. Does anyone have any ideas? The throttle body is clean enough to come from the show room floor but I have never looked at the IAC valve. Not that I would think the IAC would have anything to do with idle with lower temps.

Is there an air temp sensor on the 2004 2.7 that might be the problem?

 

Have you used any non sensor safe silicone on any gaskets recently? around the intake, maf, TB, airbox, etc?

 

No, none at all.

 

When I purchased my Tacoma it didn't even idle on a cold start. What's your mileage?
Anyways it was so bad I had to hold the RPM up a little so it could idle. I changed spark plugs, wires, cap and rotor, and nothing.
So I removed the throttle body and sure enough it was all gunked up. Cleaned the passages for the IAV and throttle body.
Ran a can of seafoam thru the intake and problem solved.

 

I get around 20mpg. It goes up and down depending on how much I idle it and whether or not I spend a day driving around on dirt trails. I idle it A LOT in the winter. I don't even bother to shut it off if I'm stopping somewhere for 5 minutes or less. I took off my air cleaner a while back and looked inside the throttle body. Nothing in there. It was clean as a whistle. The IAC is something I have never looked at though. I may do it next summer. The idle isn't bad it's just that it idles slightly rough when the temps drop. My truck never gets up to 180 degrees in the winter except for once in a while. It runs at about 175 to 179 on the interstate at 75 mph and I've seen it as low as 173 degrees on real cold days. it only idles slightly rough in the winter. Idles perfect in the summer when it's up above 180 degrees. Even in the summer on a 90 degree day i hae to really thrash it to get it up over 184 degrees. I'm beginning to think the thermostat is sticking open just a little. It is the original and the truck has about 154,000 on it. Or, it just might be the water temp sensor.

 

The engine coolant temperature sensor is mounted to the back side of the cylinder head, not easy to get to, but a likely suspect.
The sensor (aka sender) near the thermostat sends its signal to the dash temp gauge.

 

I really appreciate your info,
tan4x4 I'll look around and locate the sensor on the back side of the cylinder head. I have suspected a bad thermostat or a sensor since it only idles slightly rough when it gets cold. I just ordered a grill cover since it gets pretty cold where I live (down near, or below zero at times) and I'll probably order those sensors so I have them just in case. I'll just replace the thermostat, and both sensors next summer when I change the coolant.