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Low rpm on Drive


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Good day everyone!  this is the situation: On a warmed-up car, when you stop at a traffic light, the idle speed becomes 500rpm.  This is too low, I noticed that when you stand at a traffic light and press the brakes several times in a row, the idle speed becomes higher, but then it drops again to 500rpm.  It's been done: Throttle Body Clean, Spark Plugs Changed,Checked with smoke for vacuum leaks, No check engine light and other, PCV Replaced.  And another question, when is the vacuum pump turned on?  because I turned it off at all, but it did not affect the brakes in any way, I connected it to the battery - it works.  thank you all for your help!

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1 hour ago, John/Horace said:

No codes on your scanner. Dealer or better high end scanner might see codes. Some scanners only show basic obd codes.  Must be sensor that turns on vac pump I guess.

 

i use many scanners like launch, and professionals , no codes

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Nice, Good scanners used.  Were the old compressed intake manifolds seals reused when plugs were changed.

Its better to change them , small air leaks can create cylinder misfire, maybe idle issue.  Vac leaks can be tricky to find even with puffer. Does turning on  a/c increase engine idle speed, curious.

Edited by John/Horace
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14 minutes ago, John/Horace said:

Nice, Good scanners used.  Were the old compressed intake manifolds seals reused when plugs were changed.

Its better to change them , small air leaks can create cylinder misfire, maybe idle issue.  Vac leaks can be tricky to find even with puffer. Does turning on  a/c increase engine idle speed, curious.

intake seal done as well, just forget to wright. when turn on ac it goes up to 600 rpm, but sometime can drop again. When i push i little accelerator idle goes up to 600-650rpm.

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You have really covered all the usual issues, it seems. No codes is the most odd thing. As you know,  drive by wire cars controlled by very low voltage signals from throttle and pedal sensor to ecm. May have to wait for it to get a bit worse and trigger a code. Something is running right on the edge. Reseat the plugs again to throttle body, pedal, map, etc.  I hate parts throwing at cars, but on cheap wear items like CPS or map sensor I sometimes do. 

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