Thanks, appreciate your thoughts on this. I do give it some time but still a little slow. That's not my biggest issue. The "bucking" and shaking out of nowhere is concerning and not my first Bronco with issues. Ford had to repurchase my last big Bronco for many safety issues. My first one was a Sport with various problems. This is #3 and the last, I've spent way too many months of my life at Ford service. I really appreciate your advice, super helpful!
Wow that's really bad luck with these sorry to hear
Modern engines do not require a significant warm up period. Modern low-viscosity oil distributes throughout the engine much more rapidly than in the past. Within a few seconds of start, even a cold start, all internal engine components are fully bathed in engine oil.The high initial idle doesn't have anything to do with oil distribution, it's about smooth starts and heating up the catalytic converter. First, cold starts require a richer fuel/air mixture--that is the engine requires proportionally more fuel vs air than when the engine is warm. Why? Because fuel doesn't vaporize as well when cold. Back in the day, cars used to have a choke valve; you closed it to reduce the amount of air going through the carburetor. Closing off the air increased the vacuum in the carburetor, which in turn pulled more fuel into the engine. Although the methodology of starting the engine has changed--we use fuel injection rather than a carburetor--the physics remains the same: modern engines also require more fuel at startup. Instead of a choke, the PCM (powertrain control module) injects more fuel than normal. Too much fuel, however, will result in a mixture that's too rich to burn, so the PCM also opens the throttle to get more air in. The increase in fuel and air serves to increase the RPM. As soon as the PCM determines the engine will idle smoothly, however, it reduces the fuel and air entering the engine, thus your idle speed drops. The second thing the higher idle does is to heat up the catalytic converter as rapidly as possible. Catalytic converters do not function until extremely hot, so getting it up to temperature quickly reduces harmful exhaust emissions. The rich mixture on start up increases the temperature of the exhaust gas, which speeds heating of the cat. The rich mixture when cold is also the primary reason your car gets worse fuel mileage when it's cold.
There really isn't any controversy about this. Auto manufacturers USED to include a cooldown recommendation in the owner's manual of turbocharged vehicles when the only thing cooling the turbocharger was engine oil. Modern turbochargers are connected directly to the engine's cooling system, and coolant circulates even after you shut down the engine preventing the bearings from getting hot enough to overheat the oil. That's why manufacturers no longer include a cooldown recommendation for their turbocharged engines.
What are the RPM’s doing during this bucking process?
If your rpm drops down to 100 or so you better take it in and see what's wrong with it?
I think you meant to say 1,000 rpm?
See what I mean?
This is true. I practice what I do because I like to keep my focus ST alive. When I cold start it let the rpms drop on idle then start driving. I do keep it easy and it does take about 5-7 minutes on the freeway for engine oil to reach operating temp 180F. Coolant warms up faster but I always wait for oil to be at temp before going WOT.
Thanks for commenting! When was yours bucking? Mine slow speed usually when I'm slowing down. Trying to track it to give them clues which usually helps with no engine light. Between 15-27 mph. Just bummed that this was the best Bronco yet, super smooth, love the way it handles and now it bucks like the logo...
Thank you! My experience has been if you can go in and tell them this other owner had the same issue and here's what they found - so this is so helpful!
