Ruff Idle on cold start. Almost Misfire. No codes

[Spoofy]

2005 Sport Trac 4.0L has a ruff idle on a cold start up. It's almost sounding like a misfire. Engine also seems to idle too low after cold start. 400-500rpm and feels like its about to die. I can press on the gas a bit and it will get stuck at around 1000rpm for a min or 2, then it will idle down to about 600rpm. The misfire feeling starts to get alot better after driving for a few min. There are no codes at all on the computer. It has been to 2 shops. No issues with spark or injectors. There is also intermittent issues with exhaust fumes entering the cabin after the engine is warmed up, while air vents are on except when on max A/C. I figure that I have some kind of exhaust leak with the exhaust manifold going on there, but I wouldn't think that would cause the ruff idle on cold start. Engine and trans has 55k miles on them. One shop said it could be the harmonic balancer causing the issue because it's looking like it's starting to fall apart. Any ideas fellow explorer drivers?

 

[donalds]

Classic sign of intake gaskets
When the engine is warmed up everything expands closing the gap

Do a smoke test but let it sit overnight so its cold when u do it

 

[Fix4Dirt]

Classic sign of intake gaskets
When the engine is warmed up everything expands closing the gap

Do a smoke test but let it sit overnight so its cold when u do it

^^^^^ditto, donalds is an extremely knowledgable member! also had the intake gasket leak, was worse on cold start but still sucked hot LOL!!! dont elt it get that bad! although mine was a combo issue intake gasket and the iac pipe so it was a bad leak it would hit 2k in park as its idle LOL

 

[swshawaii]

See FIRST sticky from the link below. PCV elbow does NOT always throw po171/174 trouble codes.

List of Useful Threads - '01 - '05 Sport Trac Forum's Best Threads

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www.explorerforum.com

 

[swshawaii]

Good preventative maintenance.

CLEANING THE IAC MOTOR

Use CRC throttle body body cleaner instead of harsh carb cleaner.

Untitled Document

Also spray the MAF sensor filaments with contact cleaner when checking the air filter.

 

[Spoofy]

Had the truck in the shop. Replaced fan clutch, fan, water pump, harmonic balancer and the air cleaner hose. It runs a whole lot better over all now. Issues with high and low idle seem to be fixed along with shaking. It still feels like a slight misfire on cold start that gets alot better after the engine is warmed up. The misfire feeling is more noticeable now that it's not shaking from the fan and balancer replacement. The engine feels like it is slightly surging on cold start. Not a lot maybe 100 rpm for a min or 2 then that stops. Is everyone still thinking intake gaskets? If so what is the best thing I can purchase to do a smoke test? Sorry it took a while to reply. The shop had it for a week because it was an issue sourcing the fan. Thank you for the replies to my post.

 

[Dean peulen]

2005 Sport Trac 4.0L has a ruff idle on a cold start up. It's almost sounding like a misfire. Engine also seems to idle too low after cold start. 400-500rpm and feels like its about to die. I can press on the gas a bit and it will get stuck at around 1000rpm for a min or 2, then it will idle down to about 600rpm. The misfire feeling starts to get alot better after driving for a few min. There are no codes at all on the computer. It has been to 2 shops. No issues with spark or injectors. There is also intermittent issues with exhaust fumes entering the cabin after the engine is warmed up, while air vents are on except when on max A/C. I figure that I have some kind of exhaust leak with the exhaust manifold going on there, but I wouldn't think that would cause the ruff idle on cold start. Engine and trans has 55k miles on them. One shop said it could be the harmonic balancer causing the issue because it's looking like it's starting to fall apart. Any ideas fellow explorer drivers?

 

[Dean peulen]

Replace your air idle control Valve and check all intake hoses for holes or leaks .small leaks affect the idle and cold start idle up and down speeds. I Had the same problem with my explorer tried cleaning the air idle control Valve with carb cleaner helped a little didn't fix the problem. Brought new air idle value replaced one hose . Perfect. Also cleaned mass air sensor with correct spray. Never use degreaser on intake parts.