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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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Discussion Starter · #2 ·
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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Discussion Starter · #4 ·
As far as a leaking vacuum line, I haven't found any - yet.

I did find that the underside of the rubber intake duct closest to the throttle body was ripped totally through on the underside where you couldn't see it. It was actually ripped/cracked about 180 degrees around!

I bought a new piece that just arrived this week and I replaced it this morning. After driving about 15 miles, the check engine light came on! I now have 161,988 miles and a P0305 for a misfire on the #5 cylinder.

I think that #5 is the one on the passenger side at the back of the engine. I find it odd that I didn't have any check engine light until I replaced the leaking duct to the throttle body? I don't think that I disturbed the throttle body butterfly valve when I was pulling the old duct off or putting the new duct on.

Is there a way to test an ignition coil? I have not seen an NGK plug fail after just 42,000 miles. I've also not seen NGK plus sold individually. They usually come in packs of 4 or 6. I'm going to have to look to see if I kept the original plugs with 120,000 miles on them and swap them out. I know that I don't have the old ignition coils.

If I did accidentally "tweak" the throttle body butterfly valve, would that cause a P0305 and I need to go through that weird "throttle position relearn" procedure that I've read about?

I have never replaced any of the fuel injectors so they all have 161,988 miles on them. I really do not want to get into a parts replacement circus trying this or that. Is there a way to check the fuel pressure at each injector?

Thanks.
 

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Discussion Starter · #5 ·
I cleared the P0305. I suppose that I could swap the ignition coil #5 and plug #5 with #1 or #3 and see if the diagnostic code moves to the other cylinder.
 

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Yes. to check to see if it is the plug or the coil you just swap them to a different position, clear the code, and see if the code changes. That is, if it comes back again.
 

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Discussion Starter · #7 ·
My 2021 isn't going very well. I was thinking that I would go through the throttle position relearn procedure that I found and I got out my digital multimeter to test the battery. I forgot to take the two AAA batteries out of it the last time I used it and one leaked. I cleaned up the contacts but now the meter reads high on everything. A simple 1.5v AAA or AA battery reads at 1.625v, a 9v transistor radio type baettery reads about 11.25v. The battery in my truck reads 17.25v. And the battery in the FX35 reads 16.5v. I can't trust this meter anymore. What a stupid thing to have not removed those batteries.
 

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Discussion Starter · #8 ·
It's been 4 months since I started this thread and due to COVID closures, our FX35 has been sitting. I replaced the battery. The check engine light has been off. I think that the misfire code showed up after the initial drive after cleaning the throttle body with intake cleaner.

Anyway, the car seemed to run a little better after I replaced the battery. I'm wondering if a throttle closed position "code" was reset because the car didn't have anything powered for about 20 minutes.

I went through the throttle position relearn procedure that I found on YouTube. That has not seemed to make any improvement,

I have not found any vacuum leaks but this car isn't like a 1980's GM V8 with rubber vacuum lines running around all over the engine that dry and crack. Any suggestions on where to look/listen for a vacuum leak?

The car now has 162,028 miles on it or only about 260 miles since this stumble started when sitting at traffic lights with the A/C on. The car stumbles slightly when the A/C is off but it's not terrible. Since it's summer, driving without the A/C on is miserable so we've not been using the car.

There is one service station that I trust to not rip me off. Do I need to have my throttle body removed and "professionally" cleaned? Maybe he can find a vacuum leak with his diagnostic tools?

Could this be a clogged or weak fuel injector or fuel pump?

Thanks for any further suggestions.
 

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One time my 2005 FX35 suddenly booged down and stalled after I gunned it.

I had previously cleaned the throttle body. I used throttle body cleaner/swabs/rags and cleaned the butterfly flapper, I didn't remove the throttle body itself. Super simple.

So I knew it wasn't that.

But I read about a guy who had an insect in his MAF.

Son of a bitch! That was it, I sucked up a dead bee and after I carefully removed the bee - everything returned to normal.

Similar to you, I parked the FX35 a year ago due to Covid (home office). The car started had started running crappy, and was not throwing a CEL, but the code said misfire in cyl 6, and I didn't want to deal with it, so the car just sat.

Today I got it started, and it's still running poorly, so I'm gonna try the coils/plugs.
 
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