I have a 1999 Toyota 4Runner, 186K Miles, 4 Cylinder (3RZ-FE), Automatic Transmission.
A few weeks ago, I noticed the truck would begin at 1400 RPM for a couple of seconds, then jump to 2000 RPM on startup. I also noticed a slight hesitation when accelerating at low speeds on take-off. Once the car is warm, the idle would normalize and the truck would not hesitate. I cleaned the MAF sensor, Throttle Body, and IAC Valve and the problem went away for a couple of days. Now it's worse than ever. Rough start sometimes, I start the car and the RPMs bounce a lot. The car stalls/hesitates on takeoff and slow speeds. Negative 10-15 short-term fuel trim. After a while of driving, symptoms seem to go away.
Other things I have noticed but might not be related are a lack of acceleration on hills and I press the gas and the engine makes a chugging sound in the engine bay on the passenger side.
Where can I start to troubleshoot this issue??
Get a new fuel filter, then get fuel pump pressure tested.
The fuel filter solved the bouncing idle. The hesitation was caused by a faulty ECT