Hi, is a rattle in the engine while cold, but fine when warm common on a 96 zx6r, as i am thinking of buying one that does this and the owner tells me it is a common fault, but fine if it goes when warmed up. Ron

Think about how the vehicle is acting. Starts fine when cold, hard to start when warm. In these computer operated systems, the computer runs everything. Starts fine when cold: the computer has the engine in cold start mode putting more fuel in till it warms up. Temperature sending unit in the manifold sends a message to the computer telling it to stop the cold start mode and it stops dumping excess fuel into the cylinders and it runs fine. IF, mind you, IF the temperature sending unit is faulty, it's not telling the computer to stop the cold start mode and is flooding the engine with fuel cause it's sill in cold start mode. This is my take away on your situation and the temp sending unit is something to check to be sure it's functional. Check it out. I hope this WAS the answer to your problem my friend. It's typical. Luck to'ya Bro.

More than likely it is a temperature sensor that tells the engine if it is warmed up or cold it problem thinks the engine is still cold.

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lots of older vehicles have the same problem. i think its just a sign that the vehicle is getting old

replace the timing belt and every thing in the front like waterpump pulleys oil seal the whole 9 yards it's time

Did you find a fix?
Same problem, wondering how you fixed it?

Hi

The engine temperature sensor is bad. If so, the ECU assumes the engine is warm and it leans out the mixture, but you need a richer mix when cold, so it will run lousy till it actually gets warm.Check your coolant temp sensor. It may be defective and telling the computer that the engine is already warm. The computer is supposed to add extra fuel when cold to "choke" the engine until it reaches operating temp. If the sensor is reading incorrectly the computer may think its warm and not add the extra fuel to keep it running smoothly. Also check the two ground wires connected right next to the thermostat housing for loose or corroded connections. A bad ground here can also lead to running problems. If the sensors test ok have the timing checked.

Pull your diagnostic codes. The codes will tell if the sensor is not right.

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Check carb balance as this can cause primary drive gear lash as these are straight cut gears

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.

Ok, time for car school. The vehicle is operated by the computer, every electrical concept that is. When the engine is cold, it starts fine because the computer has placed it in "cold start mode", putting more fuel into the engine than normally would until Once the engine is warmed up, a temperature sending unit or temp sensor tells the computer to change to normal run mode. IF said temp sensor is faulty and is not telling the computer to make said change, it stays in cold start mode, still dumping excess fuel in the engine that is now not required, cause it's warmed up. Like keeping the choke closed on older vehicles. Now I think you can answer your own question, when this no start action is happening after warm up and it always starts fine when cold, what's the first thing you check ? Right, the unsuspected temp sensor. Change that and no more start problem. Have a wonderful day. Glad I could be of service.