On my 96 Limited with a 4L OHV, 141900 miles, once in awhile I'll be sitting at a stop light the engine will just idle rough and act like it wants to die. It doesn't, just acts like it. The trans in drive, foot on the brake, engine warm. Other than that, it runs great.
I get no codes.
Here's whats been done to it. At 139000 I changed plugs & wires, air filter, fuel filter and DPFE sensor.
I also get a strong smell of fuel sometimes, but not at the same time as when it starts to die.
I don't know if the two are related.
Anyone have an idea? or has it happened to them?
I'm at a loss, I can't duplicate the symptoms at home.

 

Could be intermittently sticking Idle Air Control (Idle Speed Control, old name), it's a solenoid which moves a spool valve to keep idle speed constant. Can try cleaning it, if when removed, lots of black gunk visible in passages, some are marked "Do Not Clean", so beware. A new one might be worth the cost.

 

There are a lot of items that can cause the symptoms you describe. It's going to take some further troubleshooting to determine the likely cause, or you can shotgun a few parts. As mentioned above, it could be the Idle Air Control (IAC), but that would tend to cause more drastic issues when the engine is cold. It could be a vacuum line that is cracked and expands further when warm, causing a misfire condition. Knowing the Short Term Fuel Trim (STFT) and/or the O2 sensor voltages when the roughness occurs happens could help diagnose this. You might have a spark plug wire, spark plug, or fuel injector that is failing when hot as well. Again, knowing if the engine goes rich or lean when it starts to idle rough will help diagnose this.

A couple of common items that could cause rough idle and not necessarily trigger a diagnostic code would be a cracked PCV elbow (vacuum leak) or a leaking intake manifold gasket (vacuum leak).

-Rod

 

Ok I went out today and cleaned the IAC, drove for about 10 miles and it still does it. I have 18in of steady vacuum at idle. I checked the PCV elbow and its good.
The plugs and wires were replaced about 2000 miles ago. So now I'm leaning towards a bad injector. Unfortunately my scaner is a read-only type.
I did replace Bank1 Sensor O2 sensor when I did the tune-up.
Now could the fuel smell be related? It doesn't happen at the same time.
Thanks for the help
PJ

 

Is the fuel smell from under the hood or out the exhaust?

-Rod

 

I smell it more when I'm sitting in the seat windows down and engine running. Either stopped or moving slow.
I stuggled with this because I wanted to make sure it wasn't anything else around me. It happens when the engine's warm. I smell it for a minute or so and then it disappears. the gas cap is good.
I'm just wondering if it could be an EVAP problem? It was a California truck.
PJ