4Runner jolting when the engine is cold

Question

I have a 3rd-gen 4Runner with 250k miles. It's started jolting hard when the engine is cold, for the first minute of driving, ever time I start the car. There was a code for the MAF sensor, which I took out and cleaned. After that, the CEL has remained off. Another recent problem, the wire to the engine temperature sensor had torn. I soldered it back together and that seems to be resolved.

The cold-start problem behaved differently once last week: after parking on a hill, stepping on the gas pedal did nothing at all. RPMs remained around 500 and the car slowly crawled forward. In both cases, the car goes completely back to normal once the engine is warm.

It's the 2.7L 4-cyl engine, manual transmission. I keep it well maintained.

Video here: https://www.youtube.com/shorts/9xC-8vjUigY

Answer 1

Rough idle when cold is usually a temperature or air flow sensor issue. The absence of codes doesn't mean your sensors are working properly, there may be electrical continuity but false readings. Rather than spending money and replacing sensors the best way to diagnose is to use an OBD reader and an app like torque to look at the sensor readings and see if they make sense. For the MAF/air temperature sensor you can blow a hairdryer into the air intake and see what happens to the readings - if air flow and temperature rise it's a good indication it's working. Oil and coolant temperature should be at or close to outside air temperature before you start, then rise as the engine heats up.

If I remember right your engine has a cold start injector system which runs only when cold, if they get clogged up, or there's another issue like a bad high pressure pump then you'll get the symptoms you describe.

It could be a stuck idle control valve as well, although you would likely notice a rough idle when warm as well. It's still worth checking, you pull it and clean it, then put it back in.