identify 90 g'marquis part

I have a 1990 grand marquis 5.0 and I am trying to identify a part.
It is located at the top of the middle of the firewall directly behind and above the engine, looking at the engine from the front grill.. It
is black plastic with one or two small gauge vacuum hoses going into it with a wired harness also.
I am not sure but I think it is a "module" named part with a three letter abbreviation name. I had a digram of it but lost it.
Thanks for any help!
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On Wed, 05 Jul 2006 20:36:47 -0400, whisper

Mounted on the firewall, you are probably looking at the MAP sensor (manifold absolute pressure).
Lugnut
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wrote:

Thank you!
another question. I have changed just about every sensor already, including the IAC TPS and the EGR valve with the solenoid sensors and the coolant temp sensor. I still get a minor hesitation from a dead stop on initial drive of the day and sometimes I get a hunting idle.
I was getting a steady check engine light to start with but replacing the IAC did away with that and I gave the throttle body a good cleaning. Now I get a check engine light for a fraction of a minute one out of every 10 starts. All codes that I had I cleared and none appear now either.
I was told the MAP sensor could be the last resort causing this problem. I can't say for sure but I think that changes in the weather, hot and humid, dank and damp, afffect this problem also.
Would I be wasting my time changing the MAP or do you think it is a possible cause.
thanks again!
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On Wed, 05 Jul 2006 21:25:15 -0400, whisper

Your problem with erratic idle is usually related to either a bad IAC or a vacuum leak. The off idle stumble sounds more like a bad TPS or signal from the TPS circuit. Maybe it has a bad connection or it is not at the correct idle voltage signal. Has anyone tried to set the idle speed with the stop screw on the throttle body? This is a frequent cause of erratic idle and off idle stumble. The stop screw must be set exactly by the book. A maladjusted stop screw will result in incorrect idle signal from the TPS. I think you are shotgunning it with parts instead of diagnosis. For the cost of a MAP sensor, you should be able to get a good diagnostic scan done by a pro to find out what it is doing and, the MAP sensor is not likely to cause erratic idle or stumble as you describe. Has anyone done a fuel pressure/delivery test? That vintage sometime experienced fuel pressure regulator problems that resulted in a rich mixture which can cause some of these problems.
Lugnut
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wrote:

Thanks for the detailed reply.
Today I first took the car to my mechanic and checked for any codes. There were none.
Next I went and purchased a new TPS and I will be putting it in later today. I am hoping this problem ends here with the new TPS. I will post after the repair and update the situation.
Thanks again!
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Does it sburn oil? If so check the vacuum hose at the back of the engine.It is 3/4 in I.D. and roughly a 90 degree angle.Sits in the middle and connects to the intake.

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wrote:

Thanks for the reply.
No, it doesn't burn a drop of oil. I have it since it was new and it runs fine, except for this recent problem. I still get approx. 25 mpg on the highway with just 132,000 total miles.
Installed the new TPS about an hour ago and so far the hesitation problem has not happened but I really had no time to drive around to really check it. I'll know more tomorrow keeping my fingers crossed. It would be nice to finally get rid of this problem.

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