Changing Engine Control Unit

[yahoo1]

Can the Engine Control Computer be altered successfully on my 2002 Escort SE? If yes, is it a relatively simple thing to do? My car has always idled too fast on cold start-up to suit me (the car does NOT have a tachometer). But, once it's warmed up, it should not idle any slower than it already does, or it would stall. I feel quite certain that the ONLY possible fix might be in adjusting the engine control unit, if it's possible to do that. Any excellent mechanics reading this who know the correct answer?
Thanks MUCH!!!!!

[Intuit]

Check for vacuum leaks.
When the engine is cold, a rich mixture is sought.
When the engine is warm, it tries to run a better balanced stoichiometric mix.

Vacuum leak introduces "unmetered" air.
This is air that doesn't flow past the MAF sensor and is therefore unaccounted for by the PCM/ECU. It can make adjustments on the back-end via O2 sensor but is limited, less accurate, slower.

On a cold (rich) engine, the unmetered air can result with more power and/or higher idle.

On a warm engine with EGR the unmetered air can cause pinging or other lean-related issues. "Unmetered" air can cause low idle or stalling.

EGR can also be source of unmetered air if it's introducing flow at unexpected times. However this air is mostly inert and would not result with additional power or higher idle. The EGR system's DPFE sensor hose can leak, possibly allow fresh air in (though probably unlikely) provided there's no pressure from the exhaust system.

Including the often overlooked evaporative fuel emissions system and brake booster, there are a lot of lines to check when looking for vac-leaks. A safety issue, consider the brake booster dead last and test braking prior to driving off.

All else failing, run a compression test and check timing.

Let us know what you find.

[Intuit]

Oh and to sort of answer your question, I don't think it's feasible to reprogram your existing PCM. What most people do (for racing purposes) is replace them... but I think that also means replacing the entire engine control system; which means most or all sensors. While more practical than trying to reverse-engineer the factory PCM, still less practical that finding the real cause of the idle issue. Remember, it wasn't sold with a low idle. So that means something is out-of-parameter.

Idle Air Control solenoid can also cause similar symptoms. But they're expensive and somewhat difficult to test. Best you can do is to remove and check it for stiffness and/or carbon build-up. Cleaning them is risky if done improperly. *Careful* cleaning can restore a stiff one back to sound operating condition.

[yahoo1]

Thanks much for your post(s), Intuit!!! You might find it interesting that I am definitely NOT a mechanic, however I have been driving for about 63 years so I have a pretty good idea about how engines SHOULD behave under various conditions. Of course I know that cold engines normally idle faster on start up, but this car, and my previous one, BOTH idled too fast on warmup, to suit me. Also, I have read probably 100's, or maybe even a thousand or so comments on all sorts of engine problems on various car forums, so I am well aware of VACUUM LEAKS, and also IDLE AIR CONTROL problems (and TPS problems, and MAF SENSOR problems, and on and on and on). But I just have a "feeling" (nothing more), that the PCM/ECU might not be programmed EXACTLY right, to give the result that I would like to see on the cold startup. This Escort has been doing this since I bought the car in Nov. of 2006, so I guess I can continue to live with the fast idle warmup indefinitely, if need be. The car's only got 66K miles on it. At least that's what the odometer shows.
So, thanks again for your post, Intuit!!!!!!!! Much obliged.

[Intuit]

I kind of know what you mean. When I cranked my '94 up it used to idle low and then slowly idle higher. This was due to a stiff Idle Air Control solenoid. I waited too long to clean it and was eventually forced into replacing it. Post replacement, I missed the lower idle experienced on initial start. Instead of crank, crank, VROOOOOOOM! It was more like crank, crank, rrrrrrrrrrrrrruuuuuunnnnn. I agree they idle much higher than need to, particularly during warmer weather. The reasoning is really based on old-tech Oxygen sensors. The idea was that engine needed to get up to operating temperature ASAP for more efficient operation. This was because the old O2 sensors had to reach a certain temperature before they could be read. Newer oxygen sensors are of course self-heating and therefore don't rely upon exhaust gases as much as the old. A warm engine does run more efficiently, but don't think it's as necessary as is let-on.

[yahoo1]

Thanks again, Intuit!!! You certainly seem to know "your stuff", when it comes to engines.
Best regards