Ok guys, My truck has been stumbling/losing rpms and wanting to die only when it is engaged in gear( reverse/drive). It does it more often if I a running AC. It wont miss a lick when driving it at speed. Only when coming to a stop. I replaced the IACV with a new one. The fuel pressure is good (32-34psi) and it doesn't drop when the engine stumbles. I searched for vacuum leaks with spraying the starter fluid around intake plenum, manifold, vac hoses,etc.. No dice...... Also, sometimes when the truck stumblesand wants to die the charging system(battery) light pops on the dash. Then as I take of it flickers and goes away.. And finally the last symptom is when running the AC and it stumbles, I give it gas and NOTHING. I can pump the gas pedal and no response, it just continues to cough and stumble until I turn off AC and the rpms jump back up.... So could my issue be an alternator, battery, MAF, ???? ANy help will be much appreciated.

 

If your fuel system is ok, I would then think to check to see if you have good plugs, wires, coils. Of course a bad or malfunctioning alternator could cause ignition trouble. Check your battery voltage at idle and then check again with 1500-3000 RPM's. This will give you the battery charging voltage from the alternator. Double check all the connections at the alternator. Does your engine stumble when the engine is cold or hot, or both?

 

Agreed on the voltage problem. The AC is both a physical load (compressor via the clutch) and electrical (clutch and three fans - two outside and one under the dash). Might want to do these tests with AC compressor clutch disconnected, or fuse associated with it pulled. In addition to cleaning up the battery terminals, while you have it diconnected, clean up the two large connectors in the under hood fuse box, plus check for any of the large fuses having corrosion where they are bolted down. When you increase the DC current being drawn by the vehicle, if you have a marginal connection it will create a voltage drop at that point, impacting everything beyond it. When you remove the high power drain, things may go back to normal. You can poke around with your meter, seeing what voltage is at the battery, then follow to other + voltage points along the path, like fuse, fuse terminal box wiring, connector, etc. Your other tests have eliminated fuel pump and fuel pressure - and if fuel filter or filter sock in tank on the pump was clogged, fuel pressure should drop quite a bit when revved up.

Seems like if was a sensor, like the throttle position sensor, this problem would not be AC / non-AC related. But TPS are good for stumble as well.

 

It stumbles both when cold and hot...It's just such an intermittent problem I am assuming it's electrical. The plugs, wires, cap/rotor are all less than 1000 miles old. Actually plugs I replaced last week..It stumbles more frequently with the AC running than when I don't use it. It's just weird, I can go a couple days without an issue then, BAM it acts up out of the blue...

 

I was thinking TPS. You could try just unplugging the TPS and see how it does. Just remember with the TPS unplugged it will idle really high. See if it stumbles. If so plug the TPS back in and move on to other things. That's what I would try.

*Disclaimer: I am not a mechanic nor do I play one on TV. Any advice followed is done at your own risk.

 

Could it have anything to do with the VSS? As it only happens when in gear, if in park/neutral it seems to stumble a bit then rpms pick back up..I will try the TPS and see what I get.

 

Sounds like an under load problem. This could be a fuel system issue indeed. Possibly early signs of the fuel pump getting weaker. I would test this by putting the vehicle in drive and apply brake. Give the engine some RPM's and hold it at around 3000. See if it stumbles or chokes out. If it happens in gear it could also be signs of a torque converter.

 

When you installed the new IACV did you calibrate it?

 

When I suspected a fuel issue, I hooked guage up to rail and ran line and guage up to windshield and drove it around for a couple days. It never dropped below 30psi, if memory serves me, when accelerating and when coming to a stop light, idling and it would stumble/sputter and act like it was gonna die the fuel psi stayed consistent @ 32-34psi. So IDK, I will try your suggestion.

 

Didn't get to work on the rover last nite, damn thunderstorms.......