Tell me the symptoms of the map sensor going bad?
I've had a few people to tell me that my map sensor may be bad but i put a code reader on it and it showed up ignition control module but i changed that and ran some fuel system cleaner through it and my truck still does alot better now, i can drive it for an hour and it doesn't start shaking and missing horribly now but the engine speed lopes when its idling or you hold it at a constant speed in park, i think this started after i got a guy to clean my throttle body out for me, could that have messed anything up?
Added (1). it's a 1988 ford f150 xlt lariat, 5.0 engiine
Depends on the year and make. If it's a newer vehicle with an electronic throttle body, cleaning it the wrong way or cleaning it and then not doing a throttle body relearn procedure can cause this.
Sounds like possibly a dirty or defective IAC which affects proper idle speeds although IAC issues are only for idle speeds. If the surging condition occurs at higher speeds/throttle angle, then possibly a bad MAP. Or you may have multiple problems.
Try cleaning the IAC and the bore it sits in of any carbon residue/soot with carb cleaner and soft towel/toothbrush, replace IAC and see if it helps… May take several cycles of cold engine/warmup/city driving cycle/stops in gear/ac engaged before the computer recalibrates proper idle speeds. A dirty IAC causes the computer to open up the pintle tip of the IAC more for good idle so cleaning or replacing it causes the computer to have to relearn what position to place the IAC tip at which alters idle speeds for a while.
Cleaning the TB can also affect how the computer responds to engine load/throttle angle/air flow so it may take a while for the computer to relearn how to control the engine, injectors, timing, etc.
A bad MAP usually shows up as throttle lag or stumble or erratic rpm's if it's not sensing manifold pressure properly which is a gauge of engine load but it can also affect idle speeds or cause surging/erratic rpm's… Test the MAP if needed but I'd start by cleaning the IAC on an older car with high miles as they can get crudded up over time and should be cleaned periodically along with cleaning the TB and MAF sensor. Run the car for a while through several startup/driving cycles and cool down and see if it helps or needs further testing.
Good idea to also clean the MAF sensor which can affect engine operation/airflow inputs to the computer… Do not touch the MAF sensor wire… Very delicate… Just remove the MAF and spray off any soot buildup with special MAF cleaner spray… Sold at parts stores.
MAP info…
http://www.aa1car.com/library/map_sensors.htm
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