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Old 06-30-2019, 03:44 PM   #1
Standard Care
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1999 Chevy Suburban won't slow down.

I have a 1999 Chevy Suburban with the 5.7 liter motor. When I let off the
gas, the truck doesn't slow down right away, it kind of coasts as if you shifted
it into neutral, and then somewhere between 3 and 10 seconds you feel the
back pressure and it starts to slow. I can have the gear shift in any position,
D, 3, 2, 1 and it acts this way.

If I disconnect the Throttle Position Sensor (TPS), the issue goes away.
When you let off the gas, the truck starts to slow right away, like a normal
vehicle. However, running with the TPS disconnected causes bad things and
so it's not a long term fix. I've replaced the TPS with a known good one and it drives the same.

A neighbor has an identical truck and it does the same thing. His has over
200k miles and it's "..done it forever, I think since new." Mine has low miles
but I haven't had it since new but it's done since I've had it.

What's causing this and what's the fix? Dealerships tell me it's the way it's
designed, nothing can be done. Some people say I need a new "chip" that
will give more power and will fix it but they can't tell me why so I'm not so
sure they know.

Thanks
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Old 06-30-2019, 08:40 PM   #2
cadillac_al
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Re: 1999 Chevy Suburban won't slow down.

Sounds normal to me. GM vehicles like to roll. They don't slow down as soon as you let off the gas like foreign vehicles.
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Old 07-01-2019, 11:24 AM   #3
Bigdav160
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Re: 1999 Chevy Suburban won't slow down.

It should not do that in manual D

The overrun clutch locks the forward sprag to give you engine breaking on the D range.

Drive highway speeds and pull the shifter down into 'D'. You should feel the deceleration. If it coast I would say the sprag is starting to go bad. If the sprag completely lets go you wouldn't be able to move forward from a stop but you could back up.
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Old 07-18-2019, 11:11 AM   #4
YoungPup1977
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Re: 1999 Chevy Suburban won't slow down.

when you use the brake it slows down right ?
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Old 07-18-2019, 01:34 PM   #5
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Re: 1999 Chevy Suburban won't slow down.

My 97 Suburban does this.

Always thought it was 'rev hang' to smooth out letting off the gas. I'm betting if you could monitor the position of the IACV, it would hang slightly open for about 3 seconds after you let off the gas, then close up. To test this, you could: Start the engine, let it warm up, as the IACV gives you high idle when cold. Wait until you are at normal idle. Disconnect the IACV. Drive it and see how it responds.
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