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Re: 1990 jeep yj 2.5L idles over 2200 after engine warms...
It may be a bad idle control valve. spray some brake cleaner or other fuel cleaning spray directly into the idle Control valve.it is located right inside where the air cleaner duct work is removed towards the fuel system This gets dirty and builds up gunk . making you car run bad. I hope this helps you. If it does, place a vote.
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You could pay a garage to diagnose the problem cheaper than throwing more parts at it. The problems may be connected or they may be different issues. Yes I would change the oil and filter, but first I would make sure the fuel system is not dumping too much fuel into the cylinders. The O2 sensor helps the computer decide on how much fuel the engine needs, along with the other sensors. And you said you have already replaced the O2 sensor. A mechanic would take a scanner and "read" the sensors and look for something out of normal range. The fuel pump and fuel filter are off the list as far as causing a rich mixture goes. I would start with the rich mixture and then see if fixing that issue takes care of the no start when hot issue. Change the oil and filter first, and see if the injector is on too much. You can watch the spray and tell - at idle it should be very light. Also look at the engine temp - is it warming up to normal 195 degrees? Can you tell if the fuel pressure regulator is blown and pouring fuel into the throttle body ? Without a scanner its going to be more difficult, but not impossible to diagnose. Let me know what you find out.
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.