Blazer accelerates for no reason - Car Troubleshooting


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Blazer accelerates for no reason

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upmaine
User

May 19, 2008, 12:41 PM

Post #1 of 3 (2996 views)

Blazer accelerates for no reason	Sign In

I have a 1999 s10 blazer and this started 2 weeks ago. When I come to a stop while my foot is on the brake all of a sudden the engine will accelerate a little. sometimes if my foot is not on the brake enough it moves forward. If I let it take off it will climb up to about 30 miles an hour by itself. then if I push on the gas pedal it will disengage and slow down. I noticed that the acceleration is much worse when the A/C is on. I also can be driving and when I take my foot off the pedal it will only slow down to about 30 miles an hour and it will stay there until I put my foot on the brake to slow down and then when it gets around 10 mph it will disengage and then it will slow down on it's on. I can watch the tack when I come to a stop and all of a sudden it will move it to about 1200 and that's when it wants to take off on it's own. Any ideas.

dave284
Enthusiast / Moderator

May 19, 2008, 6:28 PM

Post #2 of 3 (2990 views)

Re: Blazer accelerates for no reason	Sign In

You need to check for vacuum leaks around the intake/TB/airfilter assembly.....also the idle air control valve could be sticking.....injector cleaner might help.

DanD
Veteran / Moderator
DanD profile image

May 20, 2008, 4:45 AM

Post #3 of 3 (2983 views)

Re: Blazer accelerates for no reason	Sign In

Just to add to dave284 it could be one of a number of sensors that is telling the PCM (computer) that there is a load being applied to the engine when it actually is not.
For example; if the power steering pressure switch or the AC pressure switch has an intermittent short; the PCM sees this signal toggling, knowing (thinking) you have the steering turned all the way over against its stop and then off or the AC has just been turned on & off.
In turn the PCM will bump up the idle, raising it to compensate for the extra load on the engine, preventing a stall; load that is not there.
I have also seen the park/neutral switch short, telling the PCM that the gear shift was being moved from neutral to drive; like toggling a light switch on and off. Same thing was happening; the PCM would see drive and bump up the idle; then the switch would show neutral, lowering the idle. It felt like I was tapping my foot on the throttle.
Have the thing scanned; not for codes but to check sensor data. If this is a sensor problem but the sensor is staying within its parameters, it may not set a code.
A TPS (throttle position sensor) that is shorting from .5 of a volt to 1-volt at closed throttle won’t likely set a code; all the PCM thinks is that you’re doing a tap dance on the throttle.

Dan.

Canadian "EH"

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