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erratic idle speed

4247 Views 9 Replies 6 Participants Last post by  Garry Anderson
My grandaughter is having an idle problem with her 09 passion. Starts and runs normally, except that when idling it has recently started idling at about 1000 rpm, then immediately speeding up about 500 rpm, then oscillating back and forth at about a 2 or3 second rate. Isn't throwing any codes or any other abnormal behavior. I removed the air hose at the throttle body intake and couldn't see any movement of the throttle plate. Went a step further and replaaced the throttle assembly with a known-good one and it did the same thing, so I.m assuming it must be something accosiated with the fuel injection or timing. Anybody else have any kind of similar problem or ideas on the cause?
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Good question. My 450 cabrio occasionally does this as well. My only assumptions are a bad ground or a bad alternator, but I'm really not sure.
My 2008 has done this a few times in the 5 years that I've had it. I put half a can of seafoam in to the gas tank and the other half in to the crankcase. Took it for an hour highway drive shifting at 5k. I do this once a year just before I change the oil and it's been good since. I think these little engines are prone to carbon build up. If you do lots of city driving, it's good to rev it up once and a while and clean out the junk.
That’s possible solenoid failure.known issue for rough idle
The cars above are not 453s.... :)
The cars above are not 453s.... :)
My bad then thought it was like mine 453 0.9T 😁
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That’s possible solenoid failure.known issue for rough idle
My 2010 Smart 451 slowly developed rough idle over the last 5 years. It is getting worse with time, thus something must be wearing out or slowly failing over 5 years. It only has 110,000 Km (66,000 miles), so that seems too young to be having such issues.

After reading many forum posts, I tried SeaFoam, MMS, Spark Plugs, Coils, Crankshaft Position Sensor, ECU (ME) replacement, Upstream Oxygen Sensor, Compression Test/Leak-Down okay, but NONE of these items fixed the rough-idle issue.

By observing the Timing Advance Waveform with OBD2 Car Scanner Pro App, I see the timing (at idle) is erratic and goes from -5 deg (retard) to +30 deg (advance), so I am thinking there may be some connection with Camshaft Hall Sensor or Adjustable Camshaft Timing Solenoid. So today, I looked at the PWM signal driving Adjustable Camshaft Timing Solenoid and it appears to be reasonably stable, certainly not showing a 30 degree jump in PWM to effect timing adjustment. Also, I look at the Camshaft Hall Sensor and its waveform is quite stable too. But, the problem with any closed-loop control system is to figure out what component is disturbing the loop: Is the unstable RPM causing the Hall Sensor to change, or vice-versa.

So now I am thinking that Hall Sensor may be okay, because it is giving good timing information to the ECU, which leaves theTiming Solenoid to be suspect. Perhaps the solenoid is erratic on its own behalf, because the PWM input signal is not changing the solenoid's position. Sounds unlikely, but perhaps it is "sticky" and over-compensates in jumps to different angles.

The only other alternatives include loose timing chain or loose tensioner, both mechanical issues outside of the ECU control domain.

If anybody has any ideas, I would like to hear them.

Garry Anderson
Mobile 604-805-2555
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Rough Idle begins after Secondary Air Pump turns off, indicating ECU beings its "closed-loop" mode. Some other sensor must be monitored after the first 25 seconds, and that sensor is causing rough idle. Is that possible?

Text Line Plot Parallel Diagram
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Is it possible to program the ECU to never enter closed-loop mode? If so, how?
Any suggestions welcome. The secondary air pump is not the problem, however, its shut-off time gives us a clue that something else happens after shut off, and that "something" is creating the rough engine idle and extreme timing changes.
Thanks, Garry.
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