2000 Ford Mustang No engine light!

Bit hard to tell with out actually hearing a problem like this, but I would be checking air flow meter, and TPI sensor, coolant temp sensor also ensure that the plug gaps are correct.

The clue here is the backfire through the intake, this is often caused by ignition voltage leaking, when it is dark get the car into a shed with no lights on, open the bonnet with the engine running and crack the throttle, if there is any shorting in the ignition you will see it in the dark.

ECU's can be strange beasts, with in the program there is a set of parameters to which it will "self adjust" to maintain optimum engine performance, once any of these parameters goes out of range, that is when problems begin. More modern systems use a fuzzy logic, that is they can go out of parameter and sill stay within normal operating conditions, if it wanders out more than 5 times in a row, it will then set a code, engine speed to idle is not something that you normally worry about as long as it is a constant and not stepping down there should be no problem. If you alter any system, say fit a new coil that is working far more efficient than the one replaced the ECU with adjust in millisecond's they ecu is re adjusting all tune setting all the time faster than you can think about it, so what you need to consider is make sure that all wiring is secure no bare or loose connections, no vacuum leaks, clean fuel, good fuel pressure, clean air filter, and no codes, the inlet back fire will not be tuned out by the ecu it is an introduced problem that need to be eliminated.

Problems like this are sent to test us to the max, you are correct when you say that a sensor can lie to the ECU and the ecu accepts this a correct, the fail safe with this (to a point) is that the ecu will gather information from all sensors and combine the reading to make adjustment, it may over ride to a point, if one sensor is reading incorrect (but in still in range ) as the other sensors combined will give enough information for the ECU to adjust to best performance available, well this is the theory. But in the real world this is not always the case. I am leaning towards a problem with the TPI, but as I am working blind, I an having a hard time visualising this, you are probably on the right track with the DPFE but I feel that it is going to be a case of trying a new sensor and seeing what happens.

Often the fuel cap is the culprit. It the easy and first place to start, the rest of the EVAP system can get a bit nightmarish, but if you start at the cap and using a good schematic of the system, you should be able to nut it through, check carbon canister as well and all evap vacuum lines and valves carefully.

It has become popular to install high pressure radiator caps in an attempt to lower cooling system temps. While some makes and models come from the factory with and are designed for high pressure caps, raising your radiator cap's pressure above factory specs increases your cooling system's maximum operating pressure above design parameters. While raising your cooling system's maximum operating pressure does raise your cooling system's boiling point and therefore helps to avoid boil-over, it does not lower your operating temperature prior to boil-over, and simply allows your engine to continue to operate at temperatures higher than it is engineered for. Water boils at 212 degrees, and for each pound you raise the system pressure it raises the boiling point 3 degrees - Example: The 1.1 bar (16 pound) cap will have a boiling point of 260 degrees. Operating your engine at higher than acceptable temperatures can destroy your engine. We wish to point out some considerations that should be taken into account before an individual chooses this approach.

There are several possible reasons that you might be experiencing higher than normal cooling system temperatures:

†An engine malfunction or cooling system problem - increasing your cooling system pressure will not correct this problem and will quite possibly add to the problem. We recommend correcting the problem instead of using a higher pressure cap.
†Engine or body modifications have altered the performance of the cooling system or air flow through the radiator. Again, we recommend correcting the problem instead of using a higher pressure cap.
†Engine modifications have increased the HP of the engine - creating more HP means creating more heat. We recommend increasing the heat dissipation capabilities of your cooling system to match the increase in heat generation. The best way to do this is install an All-Aluminum High Performance radiator, increasing the radiator cap pressure will not help dissipate additional heat.
†Your car is being driven in a harsh (high heat) environment or is being driven hard for extended periods of time. Again, the best way to solve this problem is install a High Performance radiator, increasing the radiator cap pressure will not help dissipate heat.

Raising your cars cooling system's operating pressure increases the stress on all the other components of your cooling system. Before increasing your cooling system pressure by replacing your radiator cap with a higher rated radiator cap, check to make sure your entire cooling system is in excellent condition and all of the components are capable of handling these higher pressures. These may components include, but are not limited to:

†The radiator (all of the All-Aluminium radiators that we sell are rated to handle these higher pressures)
†Radiator hoses
†Heater hoses
†The heater core
†The water pump
†Freeze plugs
†All gaskets that come in contact with the cooling system

Increasing your cooling system pressure by installing a radiator cap that has a pressure rating higher than factory specs increases stress on the entire system. Although some race cars use high pressure caps, their cooling systems are built to handle these higher pressures (All-Aluminium brazed and welded radiators, steel braided hoses, no heater core, high performance water pump, high performance gaskets, etc). I recommend that you only use a cap with the pressure rating that your car was designed for.

If you can park the car slightly nose up this will help air escape, and if you use a filler adaptor, this keeps a head of coolant above the filler this will also aide in bleeding.

Sorry have been off line due to ongoing internet problems, I live in a remote location and we are the last to get fixed when things go wrong, where are you at with this car? Do you have it sorted yet?

I think that if you get it moving it should drop, may be get a friend to add some weight to the pull down force.

Change the fuel filter as a matter of course, you need to do this or the pump warranty will be void, check manifold vacuum with a gauge and watch what it shows a vacuum leak will sho up as a change of vacuum if you spray some degreaser around the manifold, is it is some what viscos, the vacuum will stabilise for a second or to as it is drawn into the engine and it will not do any harm as long as you don't start using tin after tin.