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Changed Thermostat Starts/Idles Roughly

Explorin'VA

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My temp. gauge always read cold so I replaced my thermostat assuming it was stuck.

Here's what I did:

Drained my coolant, took off my upper radiator hose, unbolted the thermostat housing, removed old thermostat, drilled 1/16th hole in new thermostat where pressure release valve should have been, put in new thermostat in the correct direction, bolted its housing back up, installed new upper radiator hose, refilled my coolant and burped the air out of the system. I left my lower radiator hose in for the time being.

Here's what happens when I start the truck:

Rough start that feels like a misfire, RPMS stay very low at start up and idle, idles rough, hesitates when accelerating from stop, drives fine when I pick up some speed. Check engine light comes on as soon as I put it into gear.


I have replaced the spark plugs. I also drained, refilled and burped my coolant again to make sure air wasn't in it. Neither of these helped.

Should I try putting in my old thermostat? Is my water pump bad? Check for vacuum leaks? Replace IAC valve? Maybe coolant wasnt flowing properly and i cracked a cylinder head. All I know is something happened while replacing the thermostat. I'm not sure what I should check for next. I haven't checked the trouble codes yet.

Thanks for any help.
 



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Anime

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The rough start/idle might be a fuel or ignition issue, or some sensor out of whack. You'd really want to know what those codes are to isolate possible causes.

Coolant not flowing properly doesn't tend to affect things until after the engine reaches operating temp, unless maybe there is just such a major blockage that sludge or solids in the cooling system are hitting the water pump impeller, or the water pump is seized and the engine is fighting against it to run, but I would think there would be major noise to indicate something like that.

Coolant might be fine, look into other running issues, clogged fuel filter, old fuel pump, bad spark plugs, bad wires, bad ignition coil, etc. etc.

You don't need to drill a hole in a thermostat, the ones without the air bleed hole (Stant Superstats) have a triangular hole in the valve part to bleed air. You just need to make sure that triangle is oriented upwards. It's not a bad idea though, especially on systems like the Explorers where trapped air can cause serious damage.
 






Explorin'VA

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I got codes 335-588 and 157. So it reads egr valve and maf sensor?
 






Roadrunner777

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Did you start this just because the gauge was low? I'm not trying to be mean, I am trying to get at any earlier issues.

What you describe cannot be related to cooling system work. If it happens right at start-up, then it doesn't make sense.

Something else you did caused this.

(Light Bulb Moment!)
You had to take apart the intake plumbing to do this job. A crack/leak in the system between the MAF and the throttle body could do this, I think. Or, did you disconnect the MAF to do this work? Just thinking out loud.
 






Explorin'VA

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It was as simple as cleaning the maf sensor. It's running normal now. My temp gauge still reads cold, but the needle does move slightly so I'm assuming the thermostat works.
 












Explorin'VA

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Heat is working. I took it for another drive and the rough idle is back and check engine remains on. It drives okay so I'll keep trying to figure it out.
 






Anime

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Some with a rough idle have replaced the MAF sensor and solved the issue, might be worth a shot if you can get one cheap or swap one out to check.
 






Explorin'VA

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This morning I unplugged the maf sensor and that didn't solve the issue. Is that test certain or should I still pick up another maf from the junk yard? Also what sensors revolve around the egr valve?
 






Anime

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Unplugging the MAF sensor would give worse or the same results as a bad MAF sensor, so that wouldn't tell you anything. You'd need to swap it with a known working one to see if there's any improvement.

If you get an EGR valve code, you'd want to replace the EGR valve. Other related sensors would likely throw their own codes. I'd suggest replacing the MAF sensor first though, and the EGR code may go away, some bad parts trigger codes in other parts because it causes them to go out of spec.
 






Explorin'VA

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I replaced the MAF sensor and my Explorer's running smoothly again. I cleaned my old sensor a couple of times and it would help for a short period but the hesitation out of 1st gear gradually got worse. I was just due for a new one. I went with Cardone over Motorcraft because it was much cheaper.

Thanks for all the help :thumbsup:
 






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