S-197 RPMs drop after filling up / Vacuum Leak Diagnostics~
 

Why is my car doing this? I've noticed all year if I get below 1/4 a tank of gas and fill it up, it will nearly stall at idle until I give it gas. I have no issues while driving, only at idle. It will stop dropping RPMs usually after 10-20 minutes. Here is a video I recorded that shows RPMs dropping and Air/Fuel going crazy. I am not touching the throttle;


Just cleaned my CAI last month and this happened on the stock intake as well. I believe the fuel filter is inside the tank, at 30,000 miles I doubt it's dirty. My father says it could be air in the fuel pump, but I've never heard of that and I'm not sure how that wouldn't affect regular driving. Any ideas?

If you're overfilling the tank, you could be forcing fuel through the evaporative emissions system and into the engine through that route. The next time you fill up, stop a little short of completely topped or overfilled and see if it still does it.

John

Perhaps you might try the the MAF clean too. Depending on the conditions...

On the fuel cap... aren't the 2010s and up no-cap style? In any event, it'd throw a code and you'd see that on the dash display. That's what mine does anyway ('06.) I've done the loose cap once or twice.. :p

Also... when you did the various intake changes/cleanings, did you remove the battery cable and let it sit for 20 minutes, then put the cable back on and retrain the computer?

:fear: :brick:

I know, I know... silly question.. everyone does that when they mess with their intake stuff... I shouldn't even ask that.

I would check for a vacuum leak while your under the hood. I had a small pin size hole in my catch can (oil seperator) hose that made my idle mess up :)

Well I never top it off, I let the pump stop it. I can try to time it better next time and leave half a gallon to see what happens.

Yes I have the capless system, however I bought a gas cap/lock from Ford. I can try without this next time and see what happens

How do I check for vacuum leaks?

Vacuum leaks are typically checked using some introduction of a chemical to change the engine idle when the leak is encountered. Depending on the chemical that is sucked into the leak source, the engine may rev up, or rev down, or stumble. However it happens to change the engine's 'current normal', you've found a leak. Maybe there's more than one, but still.

If you go to youtube and google 'check for vacuum leak' you will see lots of videos about it.

They're all the same idea. Spray a little something here, listen for change. Spray somewhere else, listen for change... keep going until you find it... or don't.

You check any intake related hoses, as well as any gaskets/seams that are involved.

Chemicals used can be carb cleaner, WD40, water, propane, and even cigar smoke! Perhaps others even.

The problem with most of these is possible flaming up. So being careful.

I'll put two videos here for your perusal. Enjoy! And hope this helps!



Cigar smoke. Awesome. :)