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I have a 2002 EX-L with 83,000 miles. Recently, I have felt a "rumbling" while it is idling. In addition to that, I have heard a slight whistle coming from under the hood and have suffered a deplorable 13 mpg in the city at the best. My first thoughts have been a vacuum leak or an O2 sensor issue. The maintenance light has not come on at all, so I am a little perplexed. The air filter is new, and the casing is tight. Does anyone have any ideas on how to diagnose the problem? Or if you have seen this same problem, what was your resolution? Thanks in advance!
 

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A whistle usually indicates a vacuum leak. You can find it (or them) by releasing propane around the engine while it is idling. When the propane enters the leak, the engine idle will increase. Note that this is a risky procedure and should be done outdoors and with no smoking.
 

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A whistle usually indicates a vacuum leak. You can find it (or them) by releasing propane around the engine while it is idling. When the propane enters the leak, the engine idle will increase. Note that this is a risky procedure and should be done outdoors and with no smoking.
That is interesting. I don't think I have ever heard of using propane to find a vacuum leak.
 

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That is interesting. I don't think I have ever heard of using propane to find a vacuum leak.
I thought so too, I've always used carb cleaner or ether but I'll have to try this at some point. I have plenty of propane for sweating plumbing.
 

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Hey, Macarnold. You know, I've noticed the same "whistling" sound from my engine (only when it was at idle) while working on it for the past few months. The sound seems to be coming from somewhere around the intake plenum just back of the IACV. I've replaced the intake gasket and tried to pinpoint it with propane but cannot find an actual leak. I eventually fixed my rough idle and starting problem (not related to the whistling sound) and wonder if the whistling sound isn't just a normal sound associated with this 3.5 VTEC. I just don't want to see you chase the same vacuum leak "red herring" that I did, if that isn't really the root of your problem. I would check out your EGR valve (which is what my problem was). There are plenty of posts on here relating to it. It could be that your valve is (A) malfunctioning, (B) clogged with soot, (C) the ports surrounding the EGR could be clogged. My van did NOT give a check engine line for the EGR valve until about 9 mos after it started rough-idling.
 

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my 02 ody ex at 94K is doing this exact same thing, plus at rough low idle with the A/C on there's a rattling noise, when I start to give gas and rpm's go up the rattling goes away.

@ gurtljb, what did you do to "eventually fix you rough idle and starting problem"?

Thanks,
Roy
 

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My father has a Caddy and it had developed a crack in the rubber boot between the throttle body and the engine, leaking air. This sort of thing is not going to likely throw an error code, but will make idle bad. Use a vac gauge and check lines. Also remember your AC system (at least on other cars I've worked on) can use vac lines for various doors inside and those can go bad or the "vac motors" that move the doors, etc. This thread is old...what was it?
 

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Cleaned my EGR passages, throttle body intake, and IACV and then ran 1/2 ping of Seafoam in from the break master cyc booster vacuum line and it's runs very smooth now, no more rough idle, seems a little more responsive to gas pedal too. The starting improvement was very slight though...not that there was a sluggish start, just saying. Battery is under 3 years but here in TX 3 years is getting somewhat old depending on the quality of battery.

I was also told by a friend that gasoline with high amounts of Ethanol can contribute to poor gas mileage too.
 
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