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High Idle/possible run away acceleration

118K views 30 replies 22 participants last post by  Barbt1117 
#1 ·
Hey all! First let me start by saying I know a little about cars but not a lot, here is my issue.
I have a 2004 Chevy Venture when I start it sometimes it starts just fine and idles great but most of the time it idles between 1200 and 2000 rpms and I have to turn it off and on a few times to get it idle right and then when I’m driving out of know where I can feel the van pull a little bite and the I know I can take my foot off the gas and the van will take off by itself ( not supper fast but like your pressing the gas)and I have reached speeds of 70 to 75 m.p.h. without touching the gas, I stop the van and it idles around 1500r.p.m.s. to 2000 r.p.m.s. . I have the IAC replaced twice, and anything to do with the throttle cleaned of carbon and other debris there are NO floor mats in the way, and the engine light is not on.
Any ideas? Could really use the help.
 
#8 ·
Willdozer, I unfortunately do not have a widespread solution to report. As a Customer Service representative, I'm unable to provide much in the way of do-it-yourself information; however, I am on hand to check for recalls and communicate with your dealer on your behalf. Are you considering bringing your concerns to your dealers' attention?

Katie
GM Customer Service
 
#10 ·
Helo. I have an Peugeot 206 / year 2000 / 1.4 I 8 valve
I have problems whit my idle acceleration, the same like Budder


When I start it sometimes it starts just fine and idles great but most of the time it idles between 1200 and 2000 rpms and I have to turn it off and on a few times to get it idle right and then when I’m driving out of know where I can feel the van pull a little bite and the I know I can take my foot off the gas and the van will take off by itself ( not supper fast but like your pressing the gas)and I have reached speeds of 70 to 75 m.p.h. without touching the gas, I stop the van and it idles around 1500r.p.m.s. to 2000 r.p.m.s. . I have the IAC replaced twice, and anything to do with the throttle cleaned of carbon and other debris there are NO floor mats in the way, and the engine light is not on.

I have change idle air control
TPS controller
Air sensor
The two lambda probes
Air filtre

Any ideas ?i!
 
#14 ·
We have the same problem with our 2001 Chevy Venture. Ours was lurching forward by itself up to 50, but we found out the cruise control button was stuck. That stopped it from moving by itself but we are still stuck on why it's idleing. It is also stalling and pretending it is out of gas but is not. Very bad :mad:Need help
 
#18 ·
Sounds like the 84 T-Bird my wife had. Rev high at stops and went at highway speeds by itself.
Can't remember what the issue was. Then there was the time it was flooding out. The IAC was bad.
Then finally in 94 it wouldn't run well at all. Ford replaced just about every part (their diagnostic computer kept telling them different things) and it still wouldn't run.
When Ford in Dearborn told the dealer that they no longer had anyone that knew the computer system on the T-Bird I knew it was time to bail on Ford.

Went with a new Eagle Vision. I wish new cars were as roomy as that one. Today's cars have gotten too narrow and feel like fighter jet ****pits.
We love the 09 Malibu we bought to replace the Vision but still wish for for more width. The new 14 Impala isn't as wide inside as the Vision was.
 
#22 ·
Check the vacuum line on the fuel pressure regulator. A failed diaphragm on the FPR can cause varying amounts of fuel to be sucked into the intake manifold. I had strangely high idle speeds and inconsistent RPM speeds on my 2001 Olds Silhouette 3.4L engine. The vac line on the FPR was gas soaked-new FPR cured all rpm issues.
Corky
 
#26 · (Edited)
I have a 2003 3.4L Impala with the same issue, fast idle problem. I had a tech2 connected when my impala did the fast idle deal. The IAC showed 22 counts standing still and went up to 45 when it should be maybe 2 or 3 counts. The TPS showed 0 ( zero)% (rotation) , 0.45 volts. I am assuming 0.45 volts is ok. so something is commanding the IAC to open which would be the PCM. My fast idle did not start till after I replaced my cat and a few months before my downstream ox sensor. Here is what I think is happening. The IAC is being opened in response to the engine running rich or perceived as running rich. A fuel injector maybe sticking for a fraction of a second each time ...or all of the FI's. or the downstream ox sensor is picking up something. I have to say though my car runs really good lots of power off the line no hesitation at any throttle position. Not getting the best gas mileage though. So I am going to try a can of Seafoam in the gas tank. Could also be the PCM itself. Could be a bad contact or wire. I had something weird happen a long time ago and I found the connectors on the PCM were loose. So I disconnected the neg then pos leads on the battery and took both connectors off the pcm and squirted with electrical contact cleaner and reattached and whatever it was went away. Unfortunately I don't have anymore time now to look into this. Will pick this up again in the spring.
 
#27 · (Edited)
IAC counts are determined by the PCM based on target RPM and possible load (A/C, Alternator). It doesn't react to AFR.

Also, IAC counts are sent to the IAC but are not confirmed. So the PCM can send a position, but that doesn't mean the IAC is actually in that position. So, the IAC could be sticking/slipping, this causes the PCM to see rpms that are high, and command a lower IAC position until it's maxed out. But, the IAC is still allowing more air through than commanded.

This same condition can be caused by a vacuum leak or by a bad gasket on the TB.

Also, your car is MAF controlled for AFR then fine tuned via the O2's. If you're running rich, check for a leak between the MAF and TB. Also, make sure the MAF is clean.

A rich condition can also be caused by fouled or bad O2's or O2 wires. And an exhaust leak before or near the O2's do cause a rich condition too.
 
#28 · (Edited)
its not the tps although a bad one could. I have an Impala 3.4L that starting doing the fast idle. Lucky I had a tech2 hooked up at the time it did the fast idle. It showed the IAC at 20 then 40 counts. Its possible a bad PCM I kind of doubt this in most cases. I think it is in response to something else going on could be the EGR. With the ignition key off engine off I disconnected the negative then Positive battery cables from the battery I touched both together momentarily with a piece of metal, then I connected the positive then negative cables. With the key off/engine off I unplugged the EGR and drove till the CEL /MIL came on, which may be the next day. Then I drove for awhile , then with the key off/engine off I reconnected the EGR and drove till the CEL went out. My Impala has not had the fast idle since. Although it may still be in learn mode from the battery disconnect. I hooked up a HFT scanner not my tech2 and it now shows 2 codes both EGR related. Its been a couple of weeks and no fast idle though. I am thinking that the EGR may be sticking open or whatever and the PCM is increasing the idle due to this event probably being picked up by the downstream ox sensor... HRCSLAM I doubt its an air leak anywhere after the MAF. This is intermittent and air leaks usually have a systemic affect throughout the whole range , like surging at cruise speed or at idle not a constant fast idle when it does happen. If it is the IAC that is bad how come it always goes to the same idle speed. Right now I am thinking it is a bad EGR.
 
#29 ·
Your IAC counts point to a vacuum leak after the TB. The IAC is trying to close completely, but it's basically maxed out on the lowest setting.
 
#30 ·
I have replaced the Throttle Position Sensor 3 times in 5 months also the I.A.C., the Throttle body gasket , replaced the fuel filters etc and have NO Vacuum leaks so telling me I need a T.P.S. is kind of redundent it is just perplexing is what can fry the TPS so often it isn't fast enough to be a short and not slow enough to be just the sensor.
 
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