hesitation, high cold idle and poor gas mileage

[f00g00]

Try cleaning your egr valve first before anything else, mrnickleye is giving good advice there. Id clean mine for my crappy mileage but I don't have one installed and my bad mileage can be attributed to my recent installation of pace setter headers. the minute increase in performance doesn't compensate for the more recent trips to the gas station. I lost over 50 miles a tank and made sure the O2 sensor was flush when they installed it. Its only back by about 2 feet.
Maybe the performance increase is due to my wallet getting lighter and we all want lighter supras.

[IHateHacks]

Before you go ripping it apart to stare at the timing belt why don't you run a cylinder compression test? A very easy, cheap and accurate way of determining if the engine needs a rebuild. Low or uneven compression will rob you signifcantly of mpg.

My EGR valve passages were half restricted by carbon build up, could not even stick my pinky in the passage. I still saw 18.7mpg on a turbocharged motor.

[rnoswal]

There is also a cold temp sensor that helps with the cold start injector timing and richens the fuel when cold. If it always reads cold then it will always see the need to run rich. Try checking that sensor.

Russ

[sd88supra]

where would this sensor be located? the high idle only occurs when cold. But it warms up fine, and when it does it idles normally. I'm also starting to suspect that my cat is plugged up.

[mrnickleye]

Originally Posted by rnoswal

There is also a cold temp sensor that helps with the cold start injector timing and richens the fuel when cold. If it always reads cold then it will always see the need to run rich. Try checking that sensor.

Russ

Not correct.

This sensor is called the Cold Start Injector Time Switch, pg FI-112 in TSRM. It only operates during cranking and engine that is below 56*. Never after the engine is running.

When active (only while cranking the motor), it supplies 12v to the Cold Start Injector, which will open and squirt a bunch of fuel into the intake manifold.

To prevent flooding, this switch will stop working automatically (heater element inside it)if you crank the engine over for more than 12 seconds, and it hasn't started.

Quoting myself: The EGR passages on the 7m usually will plug up with miles, and then you don't get any EGR gasses thru. This problem is usually not detected (nor cause troubles)until you have to go in for an emissions test. It causes high NOx readings.
So......
You won't have idling or running troubles with plugged EGR passages, or inop valve.

[sd88supra]

Originally Posted by mrnickleye

You won't have idling or running troubles with plugged EGR passages, or inop valve.

So, what is causing my poor fuel economy, high cold idle (better yet it runs harsh when cold) and hesitation? I've driven almost 9k miles since my last full tune up (plugs, wires, brakes, compression teset, LSD change, etc). I've also noticed loss in power. I think I'll start by redoing a compression test.

[sd88supra]

i looked at the spark plugs and found oil on them. im gonna put new ones in, but can i clean the housing with carb cleaner, or should i use something else?

[mrnickleye]

Carb spray down the holes will work. Or brake cleaner spray is less strong, safer.

The oil down on the spark plugs/boots can cause a misfire. You need to fix the leak. Usually the V/C gaskets, #1 & #2. Not the center one. Not a difficult job at all.