I have a 4.9l engine surges at idle running way to rich and miss. at higher rpms .I changed fuel filter spark plugs . what can it be?

High gear strains the engine more than others, so any tune up item could cause this. Leaking vacuum line, bad air flow sensor, clogged converter or muffler, weak fuel pump or dirty fuel filter all can cause this. I have also seen rust in fuel tank go right through filters and make metallic deposits on spark plugs which will then miss at high speed first and soon at all speeds. Try pulling plugs and "reading" them first. Then test fuel pressure while running at high RPMS.

Change the air filter.
Check the Throttle position sensor and make sure there is no recall on the intake manifold.
- I had a Ford Taurus with the 3L V-6 that had an intake manifold issue similar to what you describe. The butterfly in the intake had excessive wear and would stick in a different position causing the car to idle at 1800 rpm. The "fix" was to change the intake manifold.

Also, change fuel filter, spark plugs and check distributor cap / rotor and plug wires.

Its definitely running rich (exhaust smell). With no CEL I would say its a mechanical issue more than an electrical issue but you cannot rule ANYTHING out based on description. May want to entertain the idea of plugged cats too.

GOOD LUCK !!!

When there is an engine misfire it could be gas or spark related. Or, the oxygen sensor may not be operating correctly, which controls fuel supply.

If there is a 'random misfire' then it could be an oxygen sensor causing the problem, as well, causing a rich mixture.

Good luck on this repair.

replace fuel filter first reply let me know when you change fuel filter

plz vote comment reply if you need more help

adjust the idle, check the carburator system...., also check the battery and alternator.

PO171-System to Lean (Bank 1)

Air filter cover tight?
All intake ducting tight?
Clean MAF Sensor.--CRC MAF Cleaner
Fuel Pressure Regulator?
EVAP Purge Valve-stuck open?
Vacuum leaks?
EGR System-issues?

Seems your getting a lean O2 Code,because it is trying to correct for a rich condition,as you said.

Is the Throttle Position Sensor-original?

Work on what is driving it rich,my list is a possible.

How about the fuel pressure regulator?

Ensure your spark plugs,wires (ignition coil and spark) and your filters (air and fuel) are within 2 years of installation It's erratic at 800 rpm as the engine is cold and they like the 2200 range for 3 minutes before they kick down on their own. Press the pedal twice before inserting your key. The owners manual states depending on the outside temperature, the engine will require more priming. Update if possible.

You changed everything but the temperature sending unit/sensor. That's what is your problem as far as no proper cold start. When first started and cold, the sensor tells the computer to place the engine into cold start mode, engine starts and runs because it's at a bit higher idle and getting a bit more fuel. When warmed up, the sensor, if good, will tell the computer to place the engine into normal run mode now. Have the sensor tested first. If good, the engine is not going into a higher idle and is still getting the fuel but not using it fast enough because it's flooding. Hence the fuel smell. That's the fast idle solenoid on the EFI for this and the A/C high idle when it's running.

if it is burning rich, there for it will be over fueling around low rpm i do belive, which will cause the engine to flood, im guessing after you have been low rpm then go for high rpms, it like hesitaes and takes abit of a cough then goes, if that is the case then it is overfueling.

there is a way to advance/****** the engine mixture, but id say for safe if you don't know what your doing to take it do a garage, and ask for it to be timed up with the timing strobe light :) which will stop the, over fuelling around low rpms.