How to tell if plug wier or distrbuter cap is bad 5.7 ltr 98 chevy suburben

Bad coolant temp sensor or EGR valve stuck. You can remove and test temp sensor (the one for the ECM--has only one wire) using cold and then hot water and read resistance with ohm meter.

misfire can be from plugs and also from injectors. It it is fine when it warms up I would be looking at injector tip problems from the cold.

May be a leaking or bad injector, Misfiring fm coil

Have your temp sensor checked. It may not be setting off a code but a sign of a failing temp sensor is hard starts, rough idle, until the car heats up. It sends a code to the ECM to help adjust fuel mixture. If it sends gals readings, the computer will adjust the fuel-air ratio and cause vehicle to run too lean until warmed up. Some people have had to keep pumping the gas pedal to keep it going from a bad temp sensor.

Possible TPS (Throttle Position Sensor) issue. The TPS controls idling speeds under all conditions. Although the truck may idle fine when cold, once warm, if you are encountering sputtering or stalling, the TPS could be the culprit. Other possibilities could be fouled spark plugs,bad wires, or a bad distributor cap.

check plug wiers for cracks and rubbed off insulation

check that the EGR valve is not sticking or has a vacuum leak. This valve will not operate until the engine is warm.

check also the engine coolant temp sensor (ECT). This sensor tells the engine computer that the engine has warmed up, so if it is faulty, it could be sending wrong information to the computer. If the sensor is disconnected, wires to it broken, or faulty in full cold mode, it will tell the computer that the engine is very cold, like -40F. The computer will schedule fuel for cold conditions. This is usually way too much fuel for a warm engine and it will rich misfire, idle rough, and be difficult to start warm.

The ECT has two wires going to it and is dedicated to sending information to the engine computer. It has nothing to do with your dash gauge that shows coolant temp. That sender has only one wire and is dedicated to the coolant temp gauge.

if you replaced the plugs in wires in it is still doing it id looking in to changeing the dis cap in rotor bug in the dist or you mite have bad gas in it

give a good tune up. if it still is acting up let me know

Make sure all the glow plugs are working.