peterls

First, I noticed a few times that when shifting from 1st to 2nd gear, my LS would have slight hesitation, like half a second, as if it is thinking which gear to go to. I replaced my tranny shift solenoid long ago (aftermarket) and was thinking that maybe those are not as great as OEM...

But, then I noticed that when weather is cold, like it has been lately in NorCal, the whole car feels a bit lazy and MPG goes way down, sometimes. Sometimes it drives just fine. The problem shows up mostly when I am just touching the gas pedal and driving at slower pace. When I step on it, it takes off every time, so it is hard to really notice the problem as instinctively, everyone would just step on the pedal a little harder when needed. However, when the weather is hot, or when the car is really warmed up well, like after 1 hr of driving, it shifts well, and there is no hesitation ever. It actually flies with merely a touch of the gas pedal. The difference in MPGs is: 16-17-18 mpg when cold, 20-21 when hot (in mixed city/hwy driving).

My entire electrical system, with exception of the ignition coils, is brand new, all OEM.
Throttle body was cleaned.
Engine purrs otherwise.
No problems with acceleration, although when it is lazy, it does accelerate a little slower; but when it is hot outside, it takes off like a jet.

And a few times on Golden Gate bridge where cold winds would freeze any car, I can notice sudden hesitation, although it is so slight that it feels almost like just the bridge moving (and it is moving) and those joints ruining my ride a little.

So I am really stumped as I don't know where to start from.

I know that either my EGR pipe is broken, or there is a crack somewhere else in the exhaust system, although a tiny one and it seems to move about - sometimes there is a noticeable leak (when going over bumpy streets of SF), but most of the time, there is no leak.

- Cooling system is perfectly fine.
- AT works fine other than that little problem (and don't know if the hesitation is AT related at all)
- All new spark plugs and wires and rotors (OEM except Bosch rotors)
- New air filter
- New fuel filter
- Cleaned throttle body
- Cleaned IACV but not too happy with one of the bearings, it feels a little rough, but spins freely still (shouldn't affect driving anyway, right?)

Could it be my MAF going slowly bad? Or coils maybe?

I have another ECU which is good, and I think I will replace it just to see if I get the exact same behavior.

So to sum it up: slight, intermittent hesitation when not under load or hard acceleration, at 35-50mph combined with loss of MPG and primarily in cold weather.

oh, and I don't know if it is related, but it does bother me that the car will start like a champ when warm, but takes a bit when completely cold.

Yamae

I would check the resistance of the ECT sensor when cold and hot.
Does it show within the range?
It should be about 5K ohm at 0 degrees C (= 32 degrees F) and 1/20th of it at 80 degrees C.

peterls

I will do that, since ECT sensor is not OEM, I just bought the cheapest one at Rockauto if memory serves me well.

Yamae

Some aftermarket ECT sensors show good resistance at the operating temperature around 80-85 degrees C but they tend to show too big or too small resistance at low temperature. In case of a smaller resistance, the compensation doesn't work well and the 1UZ-FE engine runs rough when cold.