I have a 1996 Blazer that has developed a rough idle. It runs fine when accelerating, but lopes and shakes on idle. Changed the plugs, wires and coil and ran some fuel injector cleaner through it first. No change. It runs rich and gets about 14mpg, instead of the usual 17. Got a random multiple cylinder misfire code. We have also done:

• New cap and rotor
• Checked all vacuum lines
• New pcv valve
• New fuel filter
• Checked and cleaned egr valve
• Checked internal fuel lines
• Replaced upper intake and fuel meter assembly gaskets
• New fpr

Before changing out the fpr, we put a fuel pressure gauge on it and it was losing fuel pressure when you shut the vehicle off. This is why we thought it might be the fpr. However, it runs the same as before. We're thinking about running another fuel pressure test to see what it tells us. Our only other thought is that we need to replace the fuel injectors. Any other thoughts? Getting pretty discouraged and don't want to spend the money on a new spider if it may not fix the problem. Thanks!

 

how many miles and when it 'lopes'-put your gauge on it and let us know what it shows. Brand of pump was? JP

 

Mine is doing the same thing. If you find out what causes it I will be very interested to know.

 

If you didn't verify that the pressure leak down was cured, you really don't know. I would do another fuel pressure test to see if you still have a leak somewhere. Did you isolate the fuel pump and retest for pressure/leak-down?

Did you replace the o-rings in the fuel metering body while you had it out?

 

Thanks for the prompt replies guys. It has almost 140k miles on it. Did another fuel pressure test tonight, but didn't read these comments til just now, so I didn't test it while it was idling really rough. When it was just idling it holds at about 57psi. When I did the leakdown test it dropped 5psi in 7 minutes. Going to try to check out/test the fuel injectors tomorrow. We haven't isolated the fuel pump to check the pressure. That might be on the agenda for tomorrow too. I thought it wasn't likely to be a bad fuel pump since its running rich and holding normal pressure while it's running. We did replace the o-rings in the fuel meter assembly, yes.

Peru Motors - what pump are you asking about? I haven't replaced the fuel pump.

 

My bad-thought you wrote that you had changed the fuel pump. Many troubles out there with aftermarket pumps..Sorry. JP