So, I have an 06 Grand Marquis and I keep getting a cylinder 5 misfire. It only seems to happen when I'm idling. So far I have replaced: spark plugs, coil packs(motorcraft), injectors, intake manifold, throttle body, tps and tps motor, maf sensor, egr valve, vacuum hoses, pcv valve, evap hose to throttle, cam position sensor, crank position sensor, I've checked the battery and alternator and they are both good. The boot for the coil is reading 14.3 volts but its like I'm getting no spark in the cylinder at idle. I'm getting pretty sick of chasing this issue. It does run fine for a while after I reset the computer... any ideas? I would just trade it in but it has sentimental value to me. Thanks for any suggestions.

 

It appears that you've replaced everything under the hood -- EXCEPT for the Idle Air Control valve.
Although the problem APPEARS to be electrical, it MAY be that the IAC valve is malfunctioning, since the problem only occurs at idle speed.
I would check the IAC valve circuitry, and CHANGE the IAC valve and gasket.

TIP: Use Loctite spray glue to fix the gasket to the valve's mating surface before installing the valve.
RockAuto.com has the valve and gasket for your 2006 Marquis.

95 MERC Engine Bay

 

Unfortunately, you replaced so many parts which are not going to single out # 5 and the AIC will have a global effect on all cylinders not just 5 so I wouldn't buy that.. I would do a compression check of # 5 and the adjacent cylinder. You could be losing the drive signal to the # 5 injector or the # 5 coil. Unfortunately, you have to look at the waveform, hanging a DVM on it isn't going to cut it.

 

It's important to note: "It only seems to happen when I'm idling."
Bad injectors or coils fail at normal engine speeds.
The major change to an idling engine is Voltage Drop, which can be caused by Idle Speed too low , Alternator weakness, weak Battery, Terminal corrosion, etc.
You said the Battery and Alternator are "good" -- but are they good ENOUGH !??
Normally, an IAC that gets no power is either "ON" or "OFF" - a sticking or partially-clogged IAC CAN effect just 1 or 2 cylinders, but is extremely rare.
A Compression Test is always a good idea, but the engine's compression ratio doesn't change when idling, nor do any of the engine's mechanical specs change that could cause the misfire.
Also: #5 cylinder is at the Driver's Side Front, right behind the Thermostat housing -- which often develops small leaks that can allow coolant to enter the #5 Spark Plug hole -- and cause a misfire. A LOT of problems with the Intake Manifold on these engines, including leaky gaskets.
Anyways, good luck -- and get back to us with how you make out with a solution.

Classic Style -- Relaxed Comfort -- Modern Performance.

 

You are guessing with someone else's money.The OP never mentioned if his cold engine has a proper idle speed or if his warm idle speed is correct which is usually how the symptoms of an AIC will show up. Basically a controlled vacuum leak.Yes, the intake manifold/ gasket can affect only one cylinder. The OP stated he changed out the manifold and gaskets, so I am assuming it was done right since that didn't fix his original problem. The OP needs to troubleshoot components or areas that will affect and single out one cylinder.Like verifying drive signal to the fuel injector and ignition coil. Your suggestion is not going to single out one cylinder. If you are so confident, why not send him the part to try, if it fixes it, he can settle up with you.

 

I'm not guessing. I'm suggesting. No money involved. You are WRONG -- AGAIN !!
The OP showed that he replaced nearly everything under the hood -- EXCEPT for the IAC Valve -- which I suggested be replaced as a precautionary measure.
Did I ever claim that the IAC IS the problem !?? OF COURSE NOT !! It's all in your addled head.
And yes, it would behoove the OP to verify the drive signals to the Coils and Injectors, and ALSO to the IAC Valve. BUT -- we don't know exactly who did what, when, or how.
Aside from all that -- You've been whacking at me since you got here, and you need to knock it off. You don't have to bad-mouth others in order to make or prove a point, UNLESS your whole purpose is to be just another internet troll.

Snorkel Removed -- Cold Air Ducted From Forward of Engine Bay. Cheapest C.A.I. Available, and it WORKS !

 

I will step in when I read some bad advice given and you do it often. When I respond, you get offended. YOU keep coming back for more in a provacative manner.
You said "I would check the IAC valve circuitry, and CHANGE the IAC valve and gasket". That makes little sense to suggest he just go out and replace the AIC when he is not experiencing the # 1 complaints of an AIC issue.Unstable, fast idle or a slow idle resulting in a stall. Carbon buildup on the AIC pintle and in its bore or far more common than the failure of the AIC actuating solenoid. Simple cleaning will solve that.You are again guessing with his money. Then you suggest using Loctite spray glue on the AIC gasket. Ford NEVER used or recommends the use of any sealant on any gasket on a throttle body.That is bad advice. Go find a gasket maker suggesting a sealant be used on their throttle body gaskets. Not Loctite but a gasket maker.
Finally, your constant promoting of Bosch as the best solution to all cures leaves you open for ridicule. You offer no proof or facts to back your claims other than information created by Bosch. Every manufacturer is going to say they are best. Even our President. If you said Bosch has worked well for me, I would have no problem with that.That's your option.

 

Hey, there, Mr. Self-Proclaimed Automotive Genius -- The IAC valve on MY Grand Marquis does NOT bolt to the Throttle Body -- it bolts to the INTAKE MANIFOLD, and is difficult to reach when installing a new valve.
Perhaps you have confused the Throttle Body with the Intake Manifold -- or perhaps you've confused the IAC Valve for the Throttle Position Sensor, which actually DOES bolt to the Throttle Body.
In any case, you seem to have NO IDEA just where the IAC attaches to the engine -- and yet YOU are telling ME that I'm giving bad advice.
Let's be sure to chalk that up as YOUR error -- as long as you're keeping track.
The spray glue holds the gasket in place to prevent damage or mis-alignment of the gasket during the somewhat-tricky IAC Valve installation.
The spray glue is not a sealer, and it was not meant to seal anything.
The spray glue IN NO WAY is detrimental to the function or operation of the IAC Valve, nor does it interfere with the sealing of the gasket.
You were just looking for something to whine about, weren't you !??
It's all good -- since you rolled up and started complaining about the "****" and, more recently, MY pictures, it appears that you are just a disgruntled man that wants so badly to be an internet troll.
We can tell by your disdain for those offended by your needlessly-offensive screeds. Yours is kind of a "blame the victim" mentality. Sad.
Your closing remark warrants attention -- because -- your comments regarding Bosch products were based on what YOU THOUGHT was meant by my listing of Bosch products as my opinion that they are "the very best" under all conditions and circumstances. That is simply NOT TRUE !!
I listed the Bosch (and other brands) EXACTLY because those products had indeed "worked out well for me", as in providing exceptional performance, longevity, and/or value. The ONLY purpose for listing those products is to help others find products that can and will perform as well, or better than, the OEM equipment, with accent on the fact that The 95 MERC was built to meet specific requirements under specific conditions.
Your blind insistence that I am connected to Bosch in some way is (and has been) just plain ridiculous -- it appears that Bosch products live inside your head -- rent free.
Try to get over it, OK !??


Snorkel Removed -- Cold Air Ducted From Forward of Engine Bay. Cheapest C.A.I. Available, and it WORKS !

 

You whine about being picked on because I have to constantly correct you and it's getting to be a full time job.Then you come back for more while displaying your stupidity and slow comprehension of what you read.. I don't give a hoot about your old, primitive 95 model and where your AIC is located.I am not even impressed with your silly pics. I am referencing the OP's 2006. That's why we are here responding to his question, Einstein. Too bad you can't get your point across without boring me with your very long, mundane responses.

BTW, if you indicate that glue isn't for sealing, if you have to use that crud to hold the AIC gasket in place to install, you are more incompetent than I thought and gave you way too much credit. You won't catch me using that stuff on my T.B and you won't catch Ford using it either. Bye, Troll. Go back under your bridge or rock now.

 

I see. Your response to my explanations for your mistakes is to double-down with the personal attacks.
I WAS expecting better from you, but you've proved yourself to be just another internet troll -- else, why the hostility !??
I find it odd that you claim that it's YOUR JOB to "correct" anybody at this Forum. It's not.
Your arrogance is boundless.
You MAY notice that I have six (6) times as many posts here as you do -- which clearly shows that YOU, the newcomer, are the internet troll.