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My check engine light has come on a couple of times, and each time the code was P0300 Random Misfire detected. According to this site, one cause could be a bad EGR. Another symptom of a bad EGR is rough idle or stalling after the engine is warm, which I also experience - it sometimes will not start after a long drive until it is cooler.

My question is, how can I check the EGR before spending the money to replace it if the actual problem is, say, the vacuum pressure? I have a '99 Intrepid, if that helps.

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2 Answers 2

up vote 2 down vote accepted

Spark plugs or coil pack issues are probably the most common cause of a random misfire. I would check those items, as they are often related to the symptoms you describe.

If you don't have a code for EGR, it is unlikely to be the source of your problems.

It's a relatively simple system, a single EGR solenoid controls exhaust gas flow from a port on the exhaust manifold to a port on the intake manifold, in response to a signal from the ECU.

Two common issues with EGR:

  1. Plugging of the intake port
  2. Failed solenoid not responding (or responding insufficiently) to ECU signal

Both of these failures are monitored by the ECU and should set a code if present.

Without a code, you can't really test for #1. Treatment involves removing upper intake manifold and cleaning the EGR port on the manifold and probably the corresponding passage on the lower intake.

The EGR valve is usually actuated on startup, so you can locate it and check/feel for movement on startup or you can apply 12v via a jumper and observe.

Hope that helps!

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Hey, thank you for a detailed answer! I changed out all of the spark plugs (which were old) and still got the issue, in all cylinders at once, which is why I started looking further up the line for problems. –  Don Mar 29 '11 at 19:49
    
When you say all cylinders at once, how are you determining that? Are there any other codes stored? –  rrhartjr Mar 29 '11 at 20:13
    
Yes, P0301, P0302, P0303, P0304, P0305 and P0306, each time there is a P0300. This seemed to me to indicate that it wasn't an individual plug or coil pack. But I'm pretty new at all of this. –  Don Mar 29 '11 at 20:16
    
Ok, so misfire on all cylinders. EGR flow is pretty insignificant, I'm not sure it could cause misfire on all cylinders. Plug wires? –  rrhartjr Mar 29 '11 at 20:24
    
An EGR valve stuck open could cause symptoms like that, and may not be detectable by OBDII. However... modern EGRs are a bit harder to test than older ones that you could check with your fingertips. –  TDHofstetter Aug 31 at 4:07

Crankshaft position sensor failure may be causing what you describe. The fix is an easy DYI job.

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This doesn't answer the OP's question at all. –  Rory Alsop Sep 3 at 8:40

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