2011 GT wont idle runs rough

2011 Mustang GT, MT, 135K miles, Completely stock car

Hi, I'm new to the forum and was hoping someone could point me in the right direction on a 2011 Mustang GT I just purchased. I'm a mechanic (20 years of exp) and familiar with these cars and all the first 3 generations of coyote engines. I bought it about 2 months ago for a couple thousand dollars because it wouldn't run.

When I got it back to my shop I found out the secondary timing chain tensioner on the driver's side had failed and the little chain snapped. It ruined the cat on that side and bent 6 valves. I removed the head, had it machined, replaced the valves and reinstalled it. All the cylinder walls and pistons looked fine on that side. Everything on the passenger side was fine.

I replaced the head gasket, head bolts, chains, guides, tensioners etc but not the phasers because the dealer told me they were on back order.

I got the engine back together and it just will not run. If i flutter the gas it will run briefly and then die out when I release the gas pedal. I also get a little backfiring noise sometimes. If I give it a shot of starting fluid in the throttle body it starts, runs and sounds great until the fluid burns off.

Things I've checked.

Compression test - Close to 180 on all cylinders
Leak down test - Almost no leakage at 85 PSI
Fuel Pressure - 40 psi at idle and goes up with throttle
Gas - New
Noid light test on injectors - good pulse
PATS - Functions correctly with the light going off with the key inserted.
Oil Pressure - Tested with an analog gauge on the sender. Has 35PSI at idle and goes up with throttle.
Removed Cats on both sides - No change
I triple checked the timing and it's correct, I've timed dozens of these over the last 10 years and never had a problem.
I tried a CAM/Crank Correlation relearn but it needs the engine to idle to do this.
No lower engine noise or rod knocking, no metal in the oil filter.
No combustion gases in the coolant.
Fresh oil and filter.
Changed the MAF sensor with a spare I had, Live Data shows a very high value, 48 G/S at 2500 RPMS. What could cause it to be registering twice the airflow needed? It has a stock Intake and filter.
I'm having trouble reading fuel trims because of how poorly it runs.

The car sat for 6 months or so before I bought it and their was a mouse nest under the intake. I looked at all the wiring very carefully and didn't see any chewed up. What could be causing it to not get correct fuel/air? I can't find any air leaks past the MAF sensor and I replaced all the gaskets associated with the head gasket repair.

Thanks

James

Vacuum leak caused by vacuum pipes perished or chewed by mice or wires to the MAF ate by the mice? It looks like you've already checked all that James. were any codes present? Did both MAF,s present the same symptoms?

Hi, thanks for replying. I didn’t see any chewed wiring, hoses or plastics. Only code was the P0300 random missfire. Both MAF, same problem.

If you unplug the MAF, does it idle? If it does, something in the MAF wiring/circuit is sus.

Crank position sensor?

hi, with the MAF unplugged it does idle a little better. Still runs real rough overall though. I haven’t checked the crank position sensor or wiring yet. I’ll check that out.

Hi, thanks for your help guys. I swapped the complete intake with another I had and it fired right up. It’s running good now. Same throttle body so I guess the injectors were clogged from sitting.

Thanks again

James

Thanks for posting back what cured it for other users experiencing the same symptoms, So Possible gummed up injectors from sitting about, or one of a few issues can happen with the intake.