I have a 98 ford ranger and have had a problem with rpm. I have a 2.5 litter 5 speed engine with a/c.
When the outside tempature rises above 60 degrees I lose control of my rpm's. Rpm's will shoot way up and not come down to normal until I stop rolling. I have changed my idle speed control valve and checked for vacuum leeks but have not found the problem.
Does anyone have any ideas?
Sam

. Check for codes--AutoZone will do it for free.
. Clean/replace Mass Airflow (MAF) sensor. A defective MAF sensor can cause surging, stalling, rough idle and other driveability problems. Air passing over the hot wire causes it to cool--the sensor converts this temperature change into an analog voltage signal to the PCM. The PCM, in turn, calculates the required fuel injector pulse width to obtain the proper air/fuel ratio.
. Ensure you are not using an oil-impregnated air filter.