P0171 - rough idle, ok when in gear.
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P0171 - rough idle, ok when in gear.
Son drives a 2001 Neon SE to school/work. Can home yesterday and car was acting up. Here is what I know and have done so far.
When you turn the key the engine starts and for the first 5 seconds the engine builds RPM to maybe 5k before it comes back down.
When it returns to be at idle the engine will continue to rev up and down. Over the course of about a full second or so it will rev up and rev down. Not too much but it is VERY noticeable.
When you put it in gear Drive or Reverse, the idle changes to be steady.
No matter if it is in gear or not, when you so much as touch the gas pedal it will rev the engine quite high and take about 2.5 full seconds do return to idle. Not normal.
I removed, inspected, sealed up anywhere vacuum hoses could be leaking. No effect
I removed the air box. No effect
With the air box, when we started the car the tube that connects the throttle body to the intake sucked down all the way to the intake. There was NO airflow through the throttle body.
I could also stick my finger in the throttle body and ever so slightly move the plate in there and the engine would rev up like when pushing the gas pedal above. (I know that makes perfect sense but just reporting).
I have sprayed 2/3 of a can of Carb Cleaner all over the engine (with someone with a fire extinguisher right next to me) and haven't heard any difference in the engine.
There is a definite HISSing noise coming from either the front or right side of the engine.
I did replace a faulty Coolant Temp Sensor about 3 weeks ago. No issues until yesterday.
I am a DIY guy and NOT a real mechanic, so I am kind of stumped.
Should the throttle body plate be stuck closed at idle and NO air be coming in when the car isn't in gear?
What does the engine taking off at startup mean? Why would that be happening?
Could this be exhaust? I don't smell any exhaust? Clogged cat converter?
He can CAREFULLY drive it to school and back, so it is getting fuel/air and not dying, and calms down when in gear, but it comes back down to idle much slower than it should still.
I have cleared the code a couple times and the CEL just comes back on.
Would a clogged PCV valve do this?
Think I should remove/clean/lube the throttle body? Go to the junkyard and pull a 'new' one?
Help and advice is appreciated!
When you turn the key the engine starts and for the first 5 seconds the engine builds RPM to maybe 5k before it comes back down.
When it returns to be at idle the engine will continue to rev up and down. Over the course of about a full second or so it will rev up and rev down. Not too much but it is VERY noticeable.
When you put it in gear Drive or Reverse, the idle changes to be steady.
No matter if it is in gear or not, when you so much as touch the gas pedal it will rev the engine quite high and take about 2.5 full seconds do return to idle. Not normal.
I removed, inspected, sealed up anywhere vacuum hoses could be leaking. No effect
I removed the air box. No effect
With the air box, when we started the car the tube that connects the throttle body to the intake sucked down all the way to the intake. There was NO airflow through the throttle body.
I could also stick my finger in the throttle body and ever so slightly move the plate in there and the engine would rev up like when pushing the gas pedal above. (I know that makes perfect sense but just reporting).
I have sprayed 2/3 of a can of Carb Cleaner all over the engine (with someone with a fire extinguisher right next to me) and haven't heard any difference in the engine.
There is a definite HISSing noise coming from either the front or right side of the engine.
I did replace a faulty Coolant Temp Sensor about 3 weeks ago. No issues until yesterday.
I am a DIY guy and NOT a real mechanic, so I am kind of stumped.
Should the throttle body plate be stuck closed at idle and NO air be coming in when the car isn't in gear?
What does the engine taking off at startup mean? Why would that be happening?
Could this be exhaust? I don't smell any exhaust? Clogged cat converter?
He can CAREFULLY drive it to school and back, so it is getting fuel/air and not dying, and calms down when in gear, but it comes back down to idle much slower than it should still.
I have cleared the code a couple times and the CEL just comes back on.
Would a clogged PCV valve do this?
Think I should remove/clean/lube the throttle body? Go to the junkyard and pull a 'new' one?
Help and advice is appreciated!
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Joined: Mar 2021
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How are the gaskets on the intake manifold? Fixing a previous issue replaced the orings over time leak air can cause issues. IAC Idle Air Control motor on air cleaner housing too might be having issues? Any codes set hook up a scanner? Could have something to do with Cam or Crank sensor going bad maybe even MAP sensor. Being the housed sucked down to intake sounds like IAC not open to allow air into it? IAC allows some air into the system with the throttle closed.