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Discussion Starter #1
Hi, I'm new here but have been on other boards for years. I already did a search and couldn't find an answer.

I have a new to me 90 Grand Marquis with a 5.0. The car has sat for a while and lurches and hesitates often. The RPM's are constantly up and down even when warmed up. I got the car free and don't want to/can't sink alot of money into her. The above to me sounds like the MAF. I, for the life of me cannot find it on this car. I googled for pics and can't seem to find a 1990. But my parts stores all have one in stock. I don't want to waste the gas to see what it looks like there (plus I don't have the $ til this weekend). My question is, where on my car is this sensor, if I have one. I don't have anything coming off the intake hose that resembles the ones I've seen but there is a harness and clip attached to a housing near the intake manifold. I undid the clip and the car seemed to idle better from doing that. Could that be it? Please help!

Great board by the way! I've lurked here before, had a '92 Sable before this one.
 

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You do not have a MAF sensor. For your problem I would change the fuel filter if not done. Also I would check the voltage of the tps sensor with ignition on but engine not running the throttle plates closed voltage should read .50-1.0 volts. Then at full throttle voltage should read 4.0 volts. I would also do a full tune up plugs, wires, and cap and rotor if need be. Also think about replacing the pcv valve. Also clean the Egr valve too.
 

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I'll agree with the tune up and checking the throttle position sensor,that should solve your problem,plus change your air filter
 

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Discussion Starter #4
You sure I don't have one? I asked AllExperts.com and they said I do have one and it's on the firewall.
 

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You do not have a MAF sensor because you have a speedensity computer which does not use a MAF sensor. The only thing I can thing of that AllExperts.com is telling you that would be on the firewall is the MAP sensor. And the only place you can mount a MAF sensor is on the Air Intake before the throttle body, Because what the MAF sensor does is tell the computer how much air is going into the engine so the computer can through just the right amount of fuel to mix with the air so you get that right amount of mixture which is 14.7:1 (14.7 parts of air to 1 part of fuel).
 

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I had that problem with a Ford P/U, and it was an O2 sensor that was throwing the RPMs off. It would jump about 500 RPMs up and down while at idle.
 
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Along the air hose near the intake manifold, there is a connector of some sort. It does not look like a MAF that I have ever seen before but if I unplug the plug going into it, the idle settles down. Not drivable because it's stalls at that point, but drops down and stays running if I give a slight amount of throttle. Any idea what that is? I really need a CHEAP fix right now. I can probably live with the high idle for another week (next payday) but if there is something that can be done for free I'm all for that!!
I did briefly check for vacuum leaks and did find one.
 

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Discussion Starter #9
Along the air hose near the intake manifold, there is a connector of some sort. It does not look like a MAF that I have ever seen before but if I unplug the plug going into it, the idle settles down. Not drivable because it's stalls at that point, but drops down and stays running if I give a slight amount of throttle. Any idea what that is? I really need a CHEAP fix right now. I can probably live with the high idle for another week (next payday) but if there is something that can be done for free I'm all for that!!
I did briefly check for vacuum leaks and did find one.
 

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that is your Manifold Absolute Pressure (MAP) Sensor. Since you unplugged it the PCM found a hard fault and goes into limp mode. That is why the Idle calmed down and why it won't really drive that well. You really need to run some self tests to find out what is going on with the car. You don't have an Air Meter (MAF) so that isn't the problem. It could be anything from a bad Throttle Position Sensor(TPS) to a Lazy O2 Sensor. I would see if there is an Auto Zone in your area that would at least get a code for you so you have some sort of direction. You will spend way more time and money by Shotgunning parts at it.
 

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Discussion Starter #11
Dunno, the map sensor is on the fire wall on the passenger side, looks just like the maf sensor w/out the housing right?....this plug is attached to the manifold and airhose
 

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You are either talking about you IAC valve which is on the side of the throttle body, and this will cause the car to stall if unpluged because it allows air into the engine when the throttle plates are closed. Or you are talking about your EGR valve which is attched to a spacer between the throttle body and upper intake manifold.
 

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I forget how it is on the cap but this should help just need to follow each wire to the cap from the plug. Here is how the cyclinders are numbered looking at the engine from the front of the car.

4 8
3 7
2 6
1 5
 

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Discussion Starter #16
*update*

I removed the TPS and cleaned it. I do not have access to a voltmeter so I can't check it. I also took off the IAB and cleaned that and the throttle body and choke plate. It did idle well for a minute or so then went back to fluctuating. I noticed if I tap on the TPS while it's running, the idle changes. Would that mean I should go ahead and replace the TPS?
 

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See the TPS might still be good just needs to be adjusted. And the IAC valve you can clean them but that really does not do much if they are no good, But to check the IAC unplug the connector on it and if the car stalls then it is still good.
 

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Discussion Starter #18
amo4387622 said:
See the TPS might still be good just needs to be adjusted. And the IAC valve you can clean them but that really does not do much if they are no good, But to check the IAC unplug the connector on it and if the car stalls then it is still good.
IAC was fine. I couldn't take the high idle anymore especially at red lights when it would surge, so I took the damn TPS off all together. That brought the idle down, ran rough but could sit at lights now. Got a new TPS this morning, ($36.00), installed it in the parts store parking lot, fired it up...................................................perfect idle!!! :driver: Check engine light went out too!!

Thanks for everyone's help!! :hy:
 
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