My issue is when I first start the truck I have to let it sit for a minute or so before I take off. If I try to take off without performing this warmup ritual it will misfire and lose power until it warms up. Once warm it smooths out and seems to run perfect. It doesn't seem to idle up like most cars do on cold starts. It goes strait to normal temp idle speed. Somewhere around 725-750 rpms. It will idle with a misfire for a minute or so and then smooth out and won't return until the next cold start. Theres not a check engine light. Ive changed the plugs, wires, cap, rotor, tps, iac, and pcv valve with no change. I had a parts store hook a scanner up to it while running and at normal op temp and the upstream o2 sensor was bouncing from .14-.900 volts. The intake air temp was 165. It was 45 outside. Its taking in air from the fender well not from the hot engine compartment. i know it will read hotter than 45 b/c it's in the manifold but 165 doesn't seem right. Is that normal?
My car has 150000 miles.
My car has an automatic transmission.
Hi. I believe the ambient air temperature sensor, which measures the intake air temperature for engine management, has failed. It is reporting a far higher temperature than the engine is getting, as you have noted. Engine management is creating a leaner mixture for the engine than it really needs during cold start, so it misfires and has low power.
Replacing this sensor should improve cold start behavior. I would recommend having a certified mechanic, such as one from YourMechanic, come to your location to determine why the car is hesitating and replace the air temperature sensor if needed.
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