2007 Mustang GT Cold Engine and Hesitation Problem


New Member
Nov 17, 2020
Clarksville, TN

You've probably read this one a thousand times: "Hey guys, having problems with my car, help me fix it." I know, I know, it gets annoying. And trust me, I've tried all I can before coming here. I hate having to sound hopeless and ask for help on this type of stuff, but this is really a last resort. I cannot find the problems I am having on any other forum posts on the internet. Similar, but not quite what I'm experiencing. And working with my tuner, Lito, is really tough having to go through email.

Let me start off with everything done to my car first (not stock):
- 4.10 Gears
- AiRaid CAI
- Off-road H-pipe
- Ford Performance 47lb Fuel Injectors
- Bosch 02 Sensors
- Bosch Fuel Rail Sensor
- ACCEL Ignition Coils (with new OE plugs)

Now let me try my best to explain this problem, and list everything I've attempted to fix this. Quick note: 0 codes, no CEL.

So when I start the car, and it's cold, it's almost undriveable. It bucks back and forth, feels like a misfire at anything under 2000 RPM, gas pedal feels really unresponsive, and everything feels clunky and clumsy.

And before you think "Okay... just let the car warm up", I do. I always try and let the car warm up for 5 minutes before going to out because that's just what I've been taught. Gotta let the car warm up and get the oil circulating before putting any type of load on the engine. But it's more then that...

This problem last really until the car reaches operating temperature at about 195F. And I'm sorry, but I just cannot wait 25 minutes for the car to fully warm up before leaving. I've never known a single vehicle where this is a requirement and quite frankly, it's getting ridiculous.

Now here's where it gets annoying... when the car fully warms up, and that bucking and feeling of misfires is gone, I get another problem (INTERMITTENT) where when I stop at a red light, or wait in the drive thru, the car surges, fan kicks on and revs between 400-1000 RPM. It normally fixes itself really quick. It happens VERY infrequently though and is EXTREMELY hard to replicate. It is also noticeably worse with A/C or heater on and happens much more frequently.

I'll list the things I've done in a attempt to fix these problems. Which weirdly and annoyingly enough all of these fixes normally fixes my problem for a couple days and then comes right back.

So I've replaced Fuel Filter, replaced 02 Sensors (Bosch), replaced Fuel Rail Sensor (Bosch), replaced coils (Accel), replaced Spark Plugs (OE Motorcraft Plugs), cleaned Air Filter, cleaned Mass Airflow Sensor, cleaned Throttle Body, replaced Intake Manifold Gaskets, sent data logs to Lito and adjusted tunes. I've done battery disconnects and followed relearn procedures. Also, NO LEAKS. Did a smoke test: nothing. No cracks or holes. Checked all connections with hoses and wires and everything checks out fine.

The weird thing is, with a lot of these things I've tried, it always seemed to work for a few days and then go right back to bad again. So I don't know if it's electrical or tune related or what.

I've heard that using the Bosch 02 Sensors as opposed to the OE Motorcraft ones can pose multiple problems. Has anyone had problems with Bosch sensors? Should I try and get Motorcraft? And what about the fuel injectors? Should I go back to stock? Are ACCEL coils bad? Just a few questions.

This is what happens when you buy a car with 160K miles that's modded with a history of 4 different owners that were probably all dumb kids with small... well ya'know.... lol

If any can help, it would be MUCH appreciate. Thanks!
  • Sponsors(?)