Does throttle valve get stuck partially open?
Fleet Mechanic
Joined: Jul 2010
Posts: 1,354
Likes: 31
From: Winnipeg
Mine was intermittent at closed throttle which made it hard to diagnose. Once I had eliminated vacuum leaks (note a vacuum leak should cause the condition - in his case what I'm guessing is a surging intermittent idle - to be constant unless its also intermittent), and I had changed the IAC to a known good one from another vehicle - I had pretty much eliminated components that could cause idle issues besides the TPS.
For the OP - when your idle is high (for instance when you sense its harder braking when coming to a stop, shift it into park and see if the idle goes high. If so and its not always like this, its likely not a vacuum leak and therefore the IAC or TPS is the culprit.
If idle returns to below <<700 rpm when you disconnect the IAC connector - this tells you the IAC is returning to its closed position with no voltage applied which indicates its likely not sticking and therefore the idle is being commanded high by the TPS. You can confirm bad TPS by reconnecting the IAC and disconnecting the TPS. You should have a normal idle at that point. Or at least that's what I recall during my issues earlier this year.
I'll see if I can find my old thread on my issue and copy the link.
For the OP - when your idle is high (for instance when you sense its harder braking when coming to a stop, shift it into park and see if the idle goes high. If so and its not always like this, its likely not a vacuum leak and therefore the IAC or TPS is the culprit.
If idle returns to below <<700 rpm when you disconnect the IAC connector - this tells you the IAC is returning to its closed position with no voltage applied which indicates its likely not sticking and therefore the idle is being commanded high by the TPS. You can confirm bad TPS by reconnecting the IAC and disconnecting the TPS. You should have a normal idle at that point. Or at least that's what I recall during my issues earlier this year.
I'll see if I can find my old thread on my issue and copy the link.
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Senior User
Joined: Jan 2008
Posts: 377
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Sorry for resurrecting an old thread. I want to report how this problem (engine resisting braking occasionally) was solved.
I found new brake pads sitting on the shelf I bought a while back but forgot. I went ahead and replaced the brake pads without expecting much (rotors were not replaced). But it solved the problem. No more braking issue for last several months, not even once. The old pads were not necessarily old in age or worn out or a no-name brand. The problem didn't start immediately after pad installation. So I never suspected brake pads. Thank you all for your suggestions.
I found new brake pads sitting on the shelf I bought a while back but forgot. I went ahead and replaced the brake pads without expecting much (rotors were not replaced). But it solved the problem. No more braking issue for last several months, not even once. The old pads were not necessarily old in age or worn out or a no-name brand. The problem didn't start immediately after pad installation. So I never suspected brake pads. Thank you all for your suggestions.
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