I have a 1990 Jeep Cherokee with some weird stalling issues.

ANSWER : Hi there. Seems that the troubleshooting is leading to the transmission. When the vehicle goes into drive or reverse, if the transmission is lock up or the converter clutch is active, the engine will stall. When tapping on or turning the driveshaft and the engine stalling could be an issue with the chassis grounds and engine grounds. A ground will not allow the engine to operate properly. The wiring on the vehicle could be rusty and not make a good connection. If you need further assistance with your engine stalling, then seek out a professional, such as one from Your Mechanic, to help you.

ANSWER : Hi there. I would believe, if the fuel tank inner liner was the issue, the stalling would occur at any fuel level. The dealer should be able to identify, any revisions to the fuel tank part number. It may be, the fuel gauge sending unit is inaccurate and your fuel tank is actually nearer to empty than you might think.

Average MPG times the fuel tank capacity may help discern this possibility. Given the stalling only occurs with a fuel tank level half or below, rules out a possible IAC (idle air control) valve causing the engine stall. Assuming, the Check Engine Light is not coming on, leads me to believe the ECM (Engine Control Module) is not recognizing the fault.

To isolate the issue, I recommend having your vehicle’s stalling issue diagnosed and repaired by a certified technician, such as one from YourMechanic.

ANSWER : Hi there. If the vehicle overheated, and you noticed a lot of coolant on the ground, it’s quite possible that either the radiator broke, a coolant hose broke or the radiator cap was damaged. When this happens, a lot of coolant spills on your hot motor (which is the odor you are smelling). This can also cause damage to critical electrical parts that help the engine start and run. It’s probably a good idea to have a professional mechanic come to your location and complete a car is hard to start inspection, so they can determine what is damaged and needs to be repaired to resolve your problems. Without knowing what is damaged, it’s hard to provide an estimate for repairs.

ANSWER : The cruise control switch could have an issue and may have shorted the contacts inside the switch terminals. For the engine stalling after pushing on the throttle pedal, there could be either a vacuum leak on the engine or the air idle control valve could be stuck causing the idle to not return correctly. Check all of the vacuum lines and the brake booster for any vacuum leaks. Tighten all of the intake bolts to ensure that they are tight and not loose. A loose intake bolt, broken or cracked vacuum hose will cause the engine idle to run erratic making the idle not steady. If you need more assistance with your engine idle issue, then seek out a professional, such as one from Your Mechanic, to help you.

ANSWER : It may be normal engine electrical drain on the battery if the vehicle sat for a month or more. Once the battery is recharged fully then you can see if it will idle again. Just jumping off and only running a few minutes may not charge the battery enough to let it idle on its own. You should use a battery charger to recharge battery and retest it to see if it still stalls. You may have a bad battery and need to relearn the idle. If it still stalls then the idle control valve may be stuck closed and need to be replaced.

ANSWER : Failures in the charging circuit (alternator, etc.) do not typically cause a rough idle. A faulty throttle position sensor and/or clogged fuel injectors can cause the engine to run roughly but those are just two among many, many potential causes of a rough running engine. What will help you is a rough idle diagnostic during which the individual cylinder firing patterns can be evaluated on a scope. Those firing patterns will allow the mechanic to see if perhaps there is "a" or a couple bad cylinders and also whether the engine is experiencing a fuel system versus ignition system problem and in which cylinders. On an engine with so many miles, 240,000 in your case, compression should be tested in each cylinder as wear in the engine could potentially cause enough imbalance, from cylinder to cylinder, to cause the engine to run roughly. You have to keep in mind that typically there will be multiple issues with an old engine, for example you could have dirty fuel injectors, a sticky EGR valve and fouled plugs due to the inevitable leakage from old valve stem oil seals, or any of a number of other combinations. The best thing to do, to see if you can get additional service life out of the engine, and you likely can, is to methodically and carefully go through the list of possibilities. YourMechanic certified technicians specialize in just that so if you set up a diagnostic, a technician will get to the bottom of this for you and give you repair options so that the engine can be restored to reasonable operating condition.

ANSWER : It certainly sounds like you are on the right track. I would recommend replacing the ECM to determine if it resolves the issue. I would also recommend checking the circuitry near this computer to be sure that no wiring problems exist. If any wiring problems exist, I would advise you to repair this issue before replacing any computers due to the fact that this alone could solve the issue. If you are in doubt about this repair, I would recommend having the vehicle inspected by a qualified technician to determine the exact cause of the issue.

ANSWER : You should have the check engine light and engine scanned to see if the engine may be running lean due to low fuel pressures or clogged injectors. You should also have the mass airflow sensor cleaned and checked for proper readings and replace if not within specifications. The vehicle runs richer in colder weather and may be the reason for not stalling. You should clean injectors, clean throttle body and idle control valve then clean mass air sensor and relearn idle.