Pontiac Repair: 91 Grand Am 2.5L, haynes repair manual, coolant temp

Question
QUESTION: As the temperatures have begun to drop at night, I am experiencing a no start situation in the morning.  Once the temperature warms up during the day, the car will start.  Mechanic checked it out and no codes to the computer...pump is OK and injector is fine.  I suspect that it is the Manifold Air Temperature sensor, but my  Haynes Repair Manual does not give a definite location of where it is located...cannot find it on the air intake housing.

First, do you agree that it likely is the MAT?  And do you know of it's location?

ANSWER: Hi Perry:
No I disagree with a IAT sensor intake air sensor. Yes it has an affect on the way the engine runs but not as big an effect as the ect engine coolant temp sensor will. On some of those older cars the sensor is actually screwed into the intake manifold sensor it's self and on in the hose or air cleaner or in the air cleaner housing. It will have 2 wires more than liekly a tan wire and a black wire. You could have a number of other things going on too the best thing to do it levae it sit overnight at a shop and let them put a scanner on the car and see what the sensors are reading when the car is cold. You could have a fuel quality issue or even a carbon build up on the back of the intake valves causing it to run poorly when it's cold out. The carbon on the valves acts like a sponge it absorbs the fuel and starves the engine of fuel at start up when it needs it the most. You may want to try using a probudt called top engine cleaner in this car before you start going crazy changing parts. Get 2 cans of it at any GM dealr ship and follow the directions on the can. This stuff works wounders and it's relativly cheap less than 8 or 9 dollars a can. Good luck :)


---------- FOLLOW-UP ----------

QUESTION: I pulled the IAT sensor and checked it and according to my readings was bad, so I replaced it.  Unfortunately this did not solve the problem.  Off to my mechanic which got it to start fine the next morning (warmer night and morning).  He tried starting it this AM after 32F temp overnight and wouldn't start.  It's getting fuel, but no spark.  Unfortunately he doesn't have the instruments to meticulously check the distributer, ECM, etc.

So off to the GM dealer.  Warmer temps the next few nights, so expect it to start.  I'll let you know what we find out.

Answer
Hey Perry:


This is a weird one. When it doesn't start it has no spark or either coil packs but yet it does have injector pulse?? I would venture to say that the problem is in the ignition module then.  Usually if you have no spark on both coils you will not have an injector pulse either due to the ignition module either completely fried or the crank shaft position sensor is bad not letting the module know that the engine it actually spinning. Very weird. Let me know what the outcome was I'm curious now.....