I've been a long time lurker, jumped on to say I'm having this exact same issue. The symptoms are very similar. For reference, I've got a 2002 XLT 4.0L 4x4 with 137k miles on her. FYI: no codes thrown at any point.
Cold start would either stall or run rough, around 300 rpm just like you. If it stalls, the truck will fire right up the second start. Once warm, runs great, no issues.
I have a question. Does your throttle hesitate just after the rough start? Mine will if I experience either a stall (and start it up on the second), or if it starts and runs rough. The hesitation on the throttle only lasts for 30 seconds or so. This is after the very low idle of 300rpm. So basically, start engine, runs at 300, jumps to 1100, hovers there for 30 seconds, then begins to lower as the engine warms. During that time, where it's running between 850-1100, the throttle hesitates when depressing gas pedal. After that, everything seems to balance out and the truck runs as it should.
These are the repairs I've done over the past year. (In chronological order)
- Fuel pump and filter: Symptoms: Similar as what is occurring now, however, truck would not start at all. If I let it sit, it would fire up no problem. After reading up on this forum and doing some troubleshooting, (smacking the bottom of the tank). The theory is a flat spot on the motor's arbor (which I read on this forum, forgot where). Which explains why it only happens when starting since the 02-03 has a return type, open loop, fuel delivery. I never opened it up to confirm though.
- Replaced IAC: No change. It was looking pretty gunked up. For $33 on amazon, got a motorcraft replacement.
- Cleaned MAF sensor: No change
- ---- no repairs for 5-7 months at this point, I've just recently started after the gremlin again ----- The following is what I've done in the past couple weeks.
- Front passenger wheel bearing hub: just mentioning
- Master Cylinder, Calipers, ABS Module, All new brake calipers, Rotors, Pads, Ebrake shoes + hardware. unrelated, just mentioning. I had a bad front passenger side caliper and pedal was sinking a bit. Thought it was the caliper internally bleeding. Had to fix it anyway. Still sinked a bit. Changed MC, still sunk a bit, decided to change ABS, pedal is much better after that. Stops on a dime now. Everyone needs brakes fully functional, right?
- Replaced EGR and PCV. The PCV was loose when inspecting, had a bit of a wiggle to it. Probably due to vibration. PCV was gummed up a bit. Not enough to cause failure, but you could feel when shaking that it wasn't as free moving as the new replacement. EGR was fine but swapped it out anyway.
- Replaced Alternator: Unrelated to issues, it went out, needed a new one. Just worth mentioning.
- Topped off coolant. I'm stupid. I didn't notice it was low =/ . After sifting through the forums and reading the temp sensor as possible cause I topped it off and got it back to the proper level.
So at this point, the symptoms have shifted a little bit. They match yours more. For example. Cold starts, and I mean cold (it's been below 0deg F lately). Starts up no problem. But after I get to work, let the truck sit until lunchtime for maybe 3 hours or so, I need to do the two start dance.
Yesterday I finally got a smoke machine to check for vacuum leaks. I've tested twice. Both tests have come back negative. HOWEVER, after both tests the truck started up perfect. I have read on the forum that intake gaskets could cause a leak when cold, then seal up once warm. Each test was performed when the engine was cold, and warm. I'm not ready to rule manifold gaskets out just yet. I'd like to smoke it out and get a stall condition afterwards. The cold/warm theory doesn't really apply in this case, as it should have leaked when cold.
What I'm planning in the coming 2 weeks:
- Valve cover gaskets: Left gasket is leaking a bit (drips every so often). So I'll use this as an opportunity to change out other parts while I've got it ripped apart.
- Intake Manifold gaskets: If the gaskets are to blame, this should fix the problem.
- Fuel Injectors: Because, why not =) I'm tearing everything open, should take on as many wear parts as I can.
- New thermostat housing w/ sensor. I ordered this shortly after topping off the coolant.
As you can see, I've got my Remington 870 loaded with a buck shot ready to rock and roll. I'm confident that the issue is either coolant sensor, or vacuum leak at the intake manifold. I'm leaning more towards the temp sensor at this point. Mainly due to the symptoms changing after topping off the coolant reservoir. Not sure if that is a coincidence.
I have recently picked up an Autel Maxisys MS906TS (purchased a family van recently, rolled the cost of the scan tool into it [my rationalization to the wife]). I'm going to take a closer look at live data on both MAF, TPS, and Temp Sensor. After looking through the forums, I have a good idea what the operating voltage range of each sensor should be.
I'm sure a lot of people will read this and say that I'm not properly diagnosing and just aimlessly throwing parts at it. Yes. You would be correct. I'm not a mechanic/technician by trade. I'm a software engineer. Having a family with two kids (both under 2 years old) my time is scarce and out weighs the cost of parts. I have to use what little time I have to my advantage and be smart with it. For me, the time I spend troubleshooting a part is about the same amount of time it would take me to replace (at least the ones mentioned [PCV, EGR, IAC]). So while some of you may think it's wasted money, for me, it's more time with the family. And I get the added benefit of not worrying about those parts failing in the near future. I'm already getting complaints from the wife about how much time I spend fixing the truck.
I'll keep you posted on what transpires after I rip into the engine. It's supposed to warm up by me next weekend, I plan to use that time to do the repairs.
Matt
