93 4.0L rough idle/stalls

[fearsome]

The temp gauge was right in the middle when I shut it off, waited 20 seconds, and then restarted for the KOER test. I assume I have to get the engine warmed up again to test the O2 sensors? Since I will be working around hot exhaust, what would be the easiest way to do this?

 

[MrShorty]

Easiest way? Backprobe connectors rather than try to work on the O2 sensor itself (like you said, it gets hot down there). Personally, I prefer to backprobe at the computer's 60 pin connector, but be careful if you do. You don't want to damage anything there.

 

[fearsome]

I haven't had a chance to backprobe the o2 sensors yet. What voltage range am I looking for at the connectors? Will the engine run with the o2 sensors disconnected while I backprobe? Also, with 250K on this engine, could it be a timing belt issue? I've heard of stretched belts or one slipping a tooth before. I'm not familiar with what the 4.0 uses.

Just for kicks I pulled the sparkplug wires off of the coil pack (one at a time) and there was no build-up of any kind in there. I'm running out of ideas here and really don't have the money to take it to a mechanic. I truly appreciate everyone's help to this point!

 

[MrShorty]

The engine will run ok with the O2 sensor disconnected, but you may not see the sensor switching back and forth. Best is to backprobe the sensor while it's still plugged into the computer. O2 sensor voltage should be 0-1 V, oscillating from low to high.

 

[fearsome]

So I just need to pierce the insulation and measure voltage while it is running?

 

[MrShorty]

That would do just fine.

 

[fearsome]

Unfortunately, I am back. I have been messing with this thing off an on for quite awhile now. I resorted to take it to a mechanic who said there was an intake leak. I replaced the intake gasket, now it leaks antifreeze. So, obviously there is still and intake leak. I need to now redo the gasket.

I started thinking though, when this problem first started happening, I could back up in reverse for about 10 feet before it would just stop. I heard a minor grinding, similar to brakes. If I put it in park or neutral and then back into reverse, I could back up about 10 more feet. It was still doing this when I took it to the mechanic.

Could both of these situations be caused by the same problem...possibly a broken flexplate or something? I am running out of ideas and even contemplating selling it for parts. Could something in the drivetrain be dragging and taxing the engine enough to make it idle and run bad?

 

[Rhett]

Could both of these situations be caused by the same problem...possibly a broken flexplate or something?

I just re-read this whole thread. Dying while idling is the problem, right?
If the engine is dying, you're getting air or fuel starvation somewhere.
You said you replaced the TPS and IAC. But is the thottle body calibrated correctly with the IAC?

The truck should idle at 500 rpm with the IAC unplugged.
If it can't do that, you need to open the throttle set screw (on the passenger side of the throttle body) until the truck will idle at 500 rpm with the IAC unplugged. Have you tried doing this yet?

 

[fearsome]

It will run, but it is running at about 500 rpm and vibrates badly. I haven't tried messing with the throttle body yet. After I put the top end back together I will give that a try.

 

[fearsome]

It will idle at 500 without adjustments. It does not idle well though. It shudders and idles very rough. I guess I wouldn't know how to calibrate the throttle body to the IAC. It is a new IAC and I am using the existing throttle body. I'd be interested in hearing more about this.

I've been avoiding checking the o2 sensors as Mr. Shorty suggested, hoping they were functioning properly since they are new. I apologize Mr. Shorty and beg you to have patience and help me once again. Can you tell me which wires to probe from the computer in the passenger kick panel? I guess I don't really understand what you mean...do I just push the probe into the connector where the wire enters?

If anyone else can offer any advice, I'd be very appreciative!! Thanks to everyone who has helped me to this point!