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Discussion Starter · #1 ·
2007, AWD with 161,750 miles.

Check Engine Light is OFF.

In park or neutral, there is no noticeable stumble. If the A/C is OFF, there is a minor stumble when waiting at a traffic light.

All spark plugs and ignition coils were replaced at 120,000 miles so I have about 42,000 miles on the replacements.

I replaced the air filter, cleaned the MAF, and filled the tank with 15 gallons of 93 Octane at 161,710 miles and that seemed to help considerably. The air filter was really dirty.

I replaced the PCV valve at 161,740 miles and that didn't make any difference.

I have not removed all of the duct work between the throttle body and he plastic resonator. I only removed the section between the resonator and the air filter intake.

Other than checking the throttle body and cleaning it, without any check engine light on for any diagnostic codes, what would be best to check next?

Is the fact that the stumble is worse with the A/C turned on, mean anything specific or is it simply because it adds an extra load on the engine.
 

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Since last evening, I have been searching on-line and I have found that there are a lot of people that suggest that twhen you have any idle issues without any check engine light on or diagnostic codes present that the throttle body needs to be removed and thoroughly cleaned with Intake/Throttle Body cleaner and that would be followed by a throttle function relearning procedure. There appears to be some disagreement on a couple of the delay/wait times between some of the steps in the procedures.

There are some people that say "DON'T TOUCH THE THROTTLE BODY!!". And one other that said that some technician at a dealership said that most cleaners will remove some "dry lubricant" that is used - I assume on the pivot ends of the throttle body butterfly.

Does the simple removal of the electrical connector from the throttle position sensor require the relearning procedure or that you most likely manually open and close the butterfly a couple of dozen times while cleaning the throttle body?

I have searched this forum and I've found nothing definitive to help me.

In 13+ years and nearly 162K miles, the throttle body on this 2007 FX35 has never been cleaned or serviced by anyone.

I would imagine that if I decided to buy a remanufactured Hitachi throttle body that I would definitely need to have all of the relearning procedures performed.
 

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I know it's been a few years since this was Posted, so just know this, that stumble is from a leaking vacuum line.
When you're AC is switched on, your engine idle is increased to spin the compressor at a more efficient speed to compress the freon.
If you take a weekend to inspect your entire vacuum system you'll find the culprit.
Good luck.
 
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