Truck Stalls in the Morning - Help me diagnose the issue

[ClubHuntRed]

Hi all,

ChevyForum wasn't much help so I have decided to come here since this site is dedicated to these trucks! I love my truck! Have plans for it down the line and this is where I plan to come for my information!

Anyway, I have a 1996 Chevy cheyenne 1500 with the 4.3L vortec. What happens is, I start the truck in the morning it starts right up just fine and because it's cold (Oklahoma) it idles at just about 1000 rpm for a while which is normal. I let it warm up for about 3-5 minutes before leaving for work.

At this point the engine will idle at about 500 or 600 rpm. When I shift it into reverse or Neutral (doesn't seem to matter which) the engine will promptly try to stall (rpm on the tach drops to 200-300 rpms) for about a second then pops back up to 500 or 600 rpm (lights also dim during this period). The truck runs absolutely fine in any other area (city, highway, no stall while braking or accelerating) which is why this is so perplexing. I had distributor cap problems last summer but that was replaced with a higher quality AC Delco part.

At first I suspected the new tranny fluid may be more viscous than the old? I replaced it with new dex VI in the summer but did not notice any problems until it started getting cold outside. These transmissions seem to really shear the fluid because I can go almost 20 mph on a flat road without ever touching the gas and new trucks these days barely go 5... You guys ever notice that? But when it did it shifting into neutral that was crossed off the list. Also had a leak from the Intake Manifold Gasket which I promptly replaced with the felpro metal replacement gasket. Didn't fix the stall problem.

What can I do to narrow it down? or even better....does someone have the answer?! lol

Thanks in advance!

 

[ClubHuntRed]

Anybody?

 

[SkyHighColorado]

I think you might need a new IAC, idle air control valve.

 

[ClubHuntRed]

Ok, I'll look into this and replace that part. If it doesn't fix it, I'll return the part and make note of it here on this thread.

Thanks =)

 

[SkyHighColorado]

Ok, I'll look into this and replace that part. If it doesn't fix it, I'll return the part and make note of it here on this thread.

Thanks =)

ok, let us know what how it goes.

 

[duanes7]

My wife's car had a similar problem. Would idle on cold mornings, and die when I tried to give it gas or shift or etc. Warm days it seemed fine. For hers it turned out to be an intake leak. Once I started checking for leaks I realized I could hear it. Cold, dense, un-metered air into the engine...

 

[twomanymontes]

Vacuum leaks seem to be the largest cause of stalling issues. Not sure if your truck has a mass air flow sensor or not, but if has one and it's gummed up it can cause all kinds of driveability issues. Try cleaning it.

 

[duanes7]

That's a good place to start. The cleaning is practically free. I also cleaned her idle speed control valve. Not sure if the Cheyenne has something similar, but again, it's an almost free thing to rule out before moving to more expensive stuff.

 

[Yeti_Owner]

Either IAC or vacuum leak (hoses/intake gasket) would be my guess.

 

[ClubHuntRed]

Took a while but got around to it. Tried cleaning IAC valve and new valve. No discernible difference between the two. Still does it. Taking IAC back to get $ back.

Funny that you say Intake Manifold Gasket leak. I just replaced the IMG because of a coolant leak. If I remember correctly, I did not have this issue at first after doing the IMG. So, I don't know if it is a IMG problem. But no more coolant leak

What vacuum lines can I check? I know there is one for the brake booster. Don't see a lot of others.

Another thing I might add, it seems it only stalls when I am modulating the brake pedal at close to 0 mph. Ya know rolling along thru a stop sign, at a red light etc.

Give you any ideas?