I’ve got an 05 that just doesn’t like to start cold, I’ve cleaned the MAF, IAC, and TB and it still surges for a few minutes when started up cold. If I give it the smallest amount of gas tho it idles fine as soon as I let off it goes back to surging to the point it stalls occasionally any ideas? Would a bad exhaust system cause this? It leaks pretty bad

 

Welcome to the forum

If it runs OK after warm up, no surging, I would replace the ECT(engine coolant temp) sensor just on speculation
Also clean/replace PCV Valve, when cold they can get sticky from oil inside until warmed up, this acts as a random vacuum leak

All gasoline engines need to be Choked on cold start
With Fuel Injection the computer has to "Choke the engine", that means rich fuel mix and high idle until coolant reaches about 140degF
Computer uses ECT sensor to "see" the temp of the engine
Computer has preset idle RPMs based on coolant/engine temp, "target idles"
Say 1,200rpms if temp is 20-40degF, 1,100 if 50-70degF, 1,000 if 80-100degF, ect
So as engine warms up idle drops and drops and drops, don't have to tap throttle, like on the old carb engines
This is all computer controlled via IAC(idle air control) Valve for RPMs and ECT sensor for temp

If ECT sensor resistance/voltage is jumping around a bit on warm up that can cause surging as computer matches RPMs to reported temp

On the engine are TWO temp devices
ECT sensor, always 2 wires, 5volt sensor, only used by the computer

Temp Sender, 1 or 2 wires, 12volts, only used by dash board temp gauge


IAC Valve, this is what computer uses to set idle RPMs, its a "control" not a sensor, a 12volt solenoid that computer can adjust the voltage to, so it opens a bit and closes a bit, very accurate control, +/- 4 RPM usually
These can be cleaned
They can stick if dirty, so if computer goes to set 1,000rpm idle and engine stays at 1,100 computer keeps lowering the voltage to IAC Valve, if valve unsticks then RPMs drop too low and computer has to increase voltage to valve to get to "target RPM" so surging up and down if IAC valve is sticking a bit where the valve needs to be at higher RPMs
But at warm engine RPMs no sticking

IAC Valve should only be replaced by Motorcraft or Hitachi brand, these are true solenoid valves, other brands use stepper type and can cause erratic idle control, not smooth as it should be