Rough or Surging Idle

[Jay]

Hope this might help someone in the future diagnose similar issue.  I could have saved myself a lot of time and effort if I had initially performed this simple check on the Fuel Pressure Regulator.

 

1989 Coupe

Issue:  Rough idle / surging or hunting idle

Symptoms: 

- black exhaust

- rough running

- hard start only after pressing accelerator

- fuel pump audibly engaging in proper sequence

 

Efforts Attempted:

- new spark plug wires 

- clean IAC valve and IAC port 

- installed new IAC valve

- clean MAF sensor

- fuel pressure test conducted with initial pressure decreasing immediately from peak / pressure constant only while engine running

 

Resolution:  Fuel Pressure Regulator replaced

 

Process for Testing Fuel Pressure Regulator (at least how I tested)

1.  Engine off and cool

2.  Remove vacuum line connected to the Fuel Pressure Regulator at the regulator

3.  Check for gas coming from the vacuum line

4.  If gas is present in the vacuum line, then replace the Fuel Pressure Regulator

[Ronnie]

Thanks for posting this.  When I get time I will add a note to the Fuel Pressure Testing tutorial here on ROJ about checking the fuel pressure regulator for gas in the vacuum line.  That is something that probably should be done before doing any of the fuel pump tests.