Rough idle, occasionally dies while driving, running out of ideas....

[tomb]

I would think extremely low idle would hurt vacuum available to the brake booster.
It would also be a factor on charging in stop and go traffic. What is your idle rpm when it is stumbling? (IN DRIVE, AND PARK/NETURAL)
Do you see a slight increase in rpm if you turn on A/C? (In netural)

 

[t.c.815]

Truck: 1992 K1500 Silverado 5.7L TBI

Symptoms: Rough idle when warm/hot, occasional stall. Very rarely, truck will also die while driving. (This occurs without any stumble, miss, or other forewarning. Engine simply cuts; on decel or cruising from what I've noticed. Never under load.) Truck maintains power/electricity [gauges, electronics, etc.] Also of note is that the truck will fire right back up without hesitation in either circumstance, as if nothing happened, and will continue on. So far, neither symptoms occur when engine is cold. This has been occurring for months.

Repairs completed so far (including unrelated repairs & maintenance):

-Intake Manifold Gasket (plus associated gaskets: Thermostat Housing, EGR, Distributor, Valve Covers, etc.)
-Throttle Body/Injector Pod Assembly fully rebuilt
-Oxygen Sensor
-Throttle Position Sensor
-Idle Air Control Valve
-Coolant Temperature Sensor/Switch #1 (for ECM/Thermostat Housing)
-Oil Pressure Sender/Switch
-Spark Plugs/Wires
-Distributor Cap/Ignition Rotor
-Ignition Coil
-EGR Valve & Vacuum Hose
-Base Timing Reset, confirmed via timing light. (Computer advance also confirmed via timing light.)
-Fuel Filter
-Multiple oil/filter changes and open element air filter cleanings
-Seafoamed intake, fuel tank, and crankcase
-PCV Valve & Hose

Additional Diagnostic Measures/Notes:

-MAP tests good for output voltage; voltage also decreases/increases smoothly with vacuum changes.
-Climbed under truck during a stumbling episode and listened to fuel pump...does not cut, stumble, or stall. Very consistent. Pitch of pump never changes.
-Battery tests good and holds charge. Connections are good.
-Visual inspection of old plugs reveals no fouling and no difference in wear between cylinders. Inspection of old wires did not indicate arcing or shorting.
-Injector pattern appears even and good. No drips or cutouts.
-No smoke of any color out exhaust
-No hard or extended starting symptoms, whether hot or cold.
-Accelerates smoothly and handles load without issue. Does not cut or stumble at WOT or on interstate. Also still has plenty of power.
-No codes ever thrown or stored
-No pinging, knocking, ticking, etc. under any circumstance.
-All fluids are clean and levels are good
-No vacuum leaks (carb cleaner test revealed nothing anywhere, and most hoses are new)

Remaining ideas:

-EGR Vacuum Solenoid (had replaced bad valve, but not the solenoid)
-Ignition Module (but that usually dies completely and suddenly...and if not, symptoms also usually present under load/acceleration as well, which is not occurring.)
-MAP Sensor (tests fine, but have heard of them going bad without being off very much or throwing codes)

I don't have the cash to throw those parts at it right now, but would like to see of anyone has any other ideas that I can implement once funds start flowing again.

When it isn't stumbling or dying (e.g. when it's cold or hasn't been driven long), it runs great. I really love this truck, which is why this is driving me so insane. I feel like I've done everything, to no avail.

Any ideas from our more experienced members or techs?

check your ground wire @ the front of the intake manifold,if that is ok check all grounds.

 

[tom joyce]

Classic Ignition Control Module issue. This is exactly how they fail. The icm grease gets old and hard, looses it's ability to conduct heat into the heat sink, and they begin to crap out....
Unfortunately it is impossible to test them when they are hot enough to act this way.
A cold test will test good, but it can be a bad module anyway.
When you replace it use an Ac Delco IMC ONLY!!!! I have installed new icms (other than Ac Delco) that crap out a few miles down the road...

 

[tom joyce]

Another place to check is the fuel pump ground. They are known to corrode enough to cause fuel pump/pressure issues. It's located on the cross member just before the fuel tank (breaks out o the fuel pump wire harness there). It wouldn't hurt to clean it up anyway.....

 

[94OldRed]

Sorry, don't mean to thread jack, but I'm having almost the exact same issues. Very low/rough idle when warm, its only died on me once though. When I drive at freeway speeds, the truck will slowly start to lose power and start to decelerate. I have to floor it to get the power back. This is a never-ending cycle on the freeway. I don't want to just start throwing parts at it so I'm not sure what to replace now.

Funny enough, I replaced the ignition control module a little over a year ago. It was an AC Delco unit as well. I'm in the same boat as you at this point. Not sure how to proceed.

 

[MouthForWar]

Sorry I've kept you all waiting, but I've been waiting for an update myself.

Truck has been in the shop for a full week and I **** you not, it died on them once, fired right back up, and hasn't done it since. They're at a loss. I gave them every situational detail, and they claim they can't get it to die again...even though it was so bad at the end I had to have it towed to them. Lol.

Looks like we'll be cutting bait and bringing her home tomorrow to continue playing cat and mouse.

I've spent the last week thinking about it and talking about it with some people; a few of you have been bringing up the module and that's where we're headed. I'll bring her home, throw a new module in it, and report back.

tomb: According to the stock tach (which may or may not be off as I hear told), her operating temp idle in park is around 400-450; around 200-250 in drive/reverse. When she starts idling rough on her own, she'll dip by around 100-200 rpm and overcorrect by another 100-200 rpm (above normal idle)....or die completely. I don't recall exactly what the cold idle is; I wanna say she starts up around 1000 or so, then kicks down to about 700-800 as she heats up, then settles down to the 400-450 (still in park) once she hits OT.

The hot idle has definitely always seemed low to me, although this thing is supposed to idle fairly low anyway (AllData says 525 in drive at OT). What you're saying makes sense though as far as the booster charging is concerned. The IAC, temp sensor, pvc, etc were among the first things I replaced, along with everything else, but no change in idle speed. I've also flashed the ECM God knows how many times for various reasons.

EDIT: I recall a temporary increase in idle of 100-200 RPM when kicking the A/C on, but I'm pretty sure it settles back down after a second. My 2008 Fusion does the same thing, actually. It's like it searches for maybe half a second.

94OldRed: That's strange. My truck will NOT stumble or die at highway speed, high rpms (like cold idle), or under acceleration/load. Only at idle or part throttle/decel, and only at operating temp.

I should mention to everyone that it is now taking a few more seconds of cranking to fire after it dies. Not terribly long, but noticeable. I now have to let it actually sit for about 5 seconds before cranking.

 

[89RCLB]

Did you ever get a chance to check your fuel pressure?

 

[MouthForWar]

Nah; it **** the bed day before my gear came in and I'd had enough. Truck needed some other **** done in the shop anyway (align, etc) so I threw in the towel and told them to take a look and see if they could figure it all out. Haha.

I asked the shop to test it, though, among other things. I'm assuming it tested out fine since they've been working on it for a week and still can't figure out what's wrong, but we'll see.

I get a full debrief tomorrow; the wife just happened to run into one of the guys from the shop this weekend. Said he'd give us a call tomorrow with the lowdown on their end.

Currently in a holding pattern.

 

[Supercharged111]

Get a number and not just a "it checked OK".

 

[MouthForWar]

Yea, I will for sure.

These guys are pretty reputable, but I haven't used them in a long time and they've got some new guys there that I don't know too well, so well see. If I get a shady answer (or a number I don't like) I'll just test it myself when I get it back and we'll go from there.