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Hey guys... I'm curious to see if anyone on here can help pinpoint the cause or possible cause for an exhaust sound issue....I've got a tricky little qwirk in my engine but haven't been able to find it yet...If I'm sitting still in neutral, clutch out and or in... the exhaust audibly changes when moving or stopped...
Just so you know... I'm not accelerating ....I'm rolling off from a stop in neutral and within a sec or two the exhaust audibly changes and when i come to a stop it changes back...I've tried it using the brake to stop as well as a down hill to uphill roll without the brake...Makes no difference... the exhaust sound still changes ... I'm curious to figure this out....Any Ideas.... Maybe speed sensor??? Was wondering if the speed sensor is used for any other reason other than for the speedometer .... It's an electronic cluster and not a cable...Thought about an inertia switch but this truck doesn't come with one...

Also... While playing around with the brake pedal I found another weird issue...If I pump the brake over and over the engine goes into a freaky stumble.... Almost sounds like its missing on a couple of cylinders when doing this... I then pump the brake several times and hold it ... for a moment the exhaust sounds really smooth and the exhaust sound I spoke of in the previous paragraph also goes away for a moment then its back again...

I've considered a vacuum leak or a bad booster but have checked for both and booster is fine... No vacuum leaks... Have used a can of b 12 and a propane tank to find a vacuum leak... None present .... HELP !! PLEASE !!!
 

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Applying the brake causes the computer to go into "Fuel deceleration cut" mode, which leans out the mixture a little.

Pumping the brake pedal causes the brake booster to use engine vacuum to function. You're stealing engine vacuum at a higher rate than the engine can supply if you pump the pedal fast enough. I would consider your low idle problem normal while repeatedly pumping the brakes.

What is your idle RPM's set at with the engine at normal temp?
 

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YOTA Master
'93 2wd P/U
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2,434 Posts
sounds like normal PAIR operation.

just untder the intake manifold is a valve with a vacuum hose attached. disconnect that vacuum hose and retest. if it stops, it is a normal noise. If not look some where else, and reattach the vacuum hose.
 
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