My engine at a idle in park is at 700 RPM. When in gear and foot on brake i noticed its at 600 rpm. I am experiencing a shake i feel in the seat. when in gear and foot on brake like at a light. Now if i preload it to 700 rpm it goes away. What would cause this. What should my idle be at when in gear and foot on brake. Is there any way to raise it.

 

Sounds a bit low, but it's not adjustable. Try cleaning the IAC valve.

 

I am going to clean the iac when I get home today. I also wonder if one of the spark plugs are bad. It's a very little shake if I have a bottle if water in my center console you can see it shake. You don't feel it when she is cold not warmed up it does not do it

 

Well i just cleaned the iac no luck. I did notice it is also shaking in park. But not as bad.

 

Sounds like a misfire to me.

 

I changed out the coils to new one's and i have the same result. I might pull the plugs and check them

 

When you pull the plugs, check them for both appearance and gap. Use only Motorcraft plugs, torque them to 28 ft/lb dry, no antiseize. Make sure you use dielectric grease in the cop boots. Wouldn't hurt to pull the whole throttle body and clean it, also clean the MAF. (Use throttle body cleaner and MAF cleaner)

 

I had new motorcraft plugs put in when I did the head gaskets a couple of months this shake started when I got it back. I cleaned the maf I also cleaned the TB on the truck. I would like to pull the plugs to look at them

 

My mechanic also hooked up his snap on scanner and it shows no misfire

 

If spark plug gap was not set correct could it cause this problem. What should it be set at this is a 2003 4.6

 

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