Misfire on cylinder 5 only at idle Give it ANY gas and misfire goes away Help/Ideas

[jj5428]

I have a 2007 Grand Prix 3800 with 250,000 miles. Runs fine when cold as the rpms is a bit higher when cold. After it warms up I get constant misfires on cylinder 5.

After the car warms up and starts to misfire if I give the car ANY gas even the slightest bit possible the misfire goes away instantly watching with my scan tool.

I replaced the following from my good running 2008 Grand Prix to troubleshoot:

ICM and coil packs
spark plug and wire to cylinder #5
Fuel Injector on cylinder #5

Tested the following:

Compression on cylinder #5 is 170# psi
Noid light on injector #5 flashes like it should
good spark to spark plug on cylinder #5

I'm thinking worm camshaft lobe or bad lifter? Is there a way to raise the idle on these drive by wire cars? 100 RPM increase seems like it would fix this issue. The car idles bad after it warms up now but it never stalls. Let it run bad and drive it as is? I just put a new cat converter on the car. It'll probably eat the catalytic converter again from the misfires if not addressed.

What would you guys recommend for this or what would you look at next to troubleshoot this issue next?

Thanks for any help!

 

[FordMan77]

Have you cleaned the MAF sensor and throttle body? The backside of the trottle plate gets gunked up and has caused weird issues before.

 

[jj5428]

MAF and TB are clean. Also swapped with known working from another car.

Interesting thing I found last night if I unplug the MAF the misfire goes away. Confirmed with 2 different MAF sensors that work fine in another car.

 

[Scottydoggs]

try tapping on the maf top, sometimes they clear up with a tap or two.

also check the maf pig tail wires for damage.