Why does my 1996 Toyota 4Runner 3.4 runs good in the winter but bad in the summer
Why does my 4Runner ,run good in the winter and bad in the summer
I have theories on this, as my boyfrind's '05 GMC has a similar issue. My theory: regular maintenance such as changing the trans fluid& filter as well as viscosity of trans fluid &/or gear oil. Higher mileage vehicles become senile.
1. It could be an ignition problem. The coils heat up and resist current then the ECU fails to conduct the electrical signal for spark. 2. Cold is hard on batteries, but hot is too. In hot weather, heat can reduce the battery's ability to send out electricity; reducing juice for ignition. Keep the battery in top shape and keep the electrical connections clean & tight. 3. In winter, coolant problems might not be that noticeable. But in hot weather, any failure can cause running problems when an engine runs too hot.