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Hello, a low idle can be caused by a vacuum leak. Check all vacuum connections and the air inlet tube connections to the throttle body. If this is ok, remove the mass air flow sensor from the air cleaner and inspect inside the sensor for a bug or any debris on the sensor heater wire. Tap it out and use a can of mass air flow cleaner or brake clean, not carburetor cleaner, that will mess up the sensor. Disconnect the battery for awhile and drive the vehicle and recheck.
Ok, how many miles are on the engine? WHat is it doing while driving besides the low idle?Good power running down the road? Passes a Key On Engine Off & Key On Engine Running Test with a scan tool?
Ok, a shudder at highway speeds can be either an engine misfire, or torque convertor shudder. Check the trans fluid level and condition, if it looks brown to black and smells burnt, a transmission service/flush should be done to see if the shudder goes away. The mechanic that looked at the truck may not have found any memory codes stored, but I dont know if he did on demand testing (Key On Engine Off & Running Tests). Also a special OBDII test called mode 6 data will show if there are any misfires happening below the threshold of it turning on a check engine light. Take a vacuum gauge and hook it up to the engine and see if the needle bounces around, with the mileage on the truck if all diagnostic checks out ok it could be a worn or burnt exhaust valve causing the rough idle. A broken valve spring will show a bouncing needle. Remove all spark plugs and inspect how they are burning, check for any coolant in the spark plug tubes and perform an engine compression test. All the cylinders should be no more than 10 percent difference otherwise it is indicating an engine issue
Hello, do you need more help with this concern?
Hello, do you need more help?