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

[chipskittles]

Sounds like you might have a brake booster leak. I don't think the C1500 used a check valve, someone else will correct me if wrong. Regardless, it would be easy to bypass your brake booster to see if this is your main issue. Just plug the line going to the booster. You won't have power brakes of course so remember that when stopping, and I would not do this longer than necessary. You will want to pull the fuse on the computer to clear your idle air settings before going out test driving in case this was in fact the problem. If you suddenly plug a large vacuum leak on a computer controlled engine the computer will freak out for a while while it relearns how to deal with no vacuum leak.

 

[Supercharged111]

Even a good booster affects idle slightly. Pedal to the floor sounds more like a master to me. Booster failure ought to cause a hard pedal, at least that's the failure I've encountered.

 

[MouthForWar]

^^^^That's what I thought too (hard pedal rather than no pedal with booster failure), but I guess I've seen stranger things happen.

I also have never seen the idle drop 400 rpm when depressed and then surge back up 600 rpm when released, then come back down to normal. Usually it's only 2-300 either way. Was just strange. Didn't see any evident leakage from master or slaves, but haven't had a chance to really inspect. Fluids level is still good too. (I know they can fail in other ways, just wanted to give detail.) I'm out of town for a couple of days so I won't be able to do anything further for a minute.

Plugging the hose did *seem* to cure the original stumble, but it's anecdotal/ coincidental I guess when considering other booster tests checked out (seeing if pedal builds & holds, then releases, vacuum with engine off and then starting it, etc.). I'll need to hook a vacuum up to be sure.

Seems like I might be chasing 2-3 simultaneous issue here, lol.

The first time I lost the pedal scared the **** out of me though; was driving down our main street. I can deal with the engine cutting off occassionally like it has been, I'm mentally prepared for that with this truck...but all of a sudden having 10% brake power without warning when I wasn't prepared to give myself extra stopping distance is not how I wanted to start that day. Lol. I got lucky there.

I've run it around a bunch of side streets and out in the county (I live in a pretty rural area, so I can choose less travelled routes to test drive things or run errands if I need to) and it hasn't happened again.

This truck is seriously messed up. Beggars can't be choosers and the truck was gifted to us for free (previous owners upgraded one of their many trucks and knew we needed at least *something*...it definitely wasn't a malicious/shady offload of a problem vehicle)...but man, I'm starting to think it's cursed. Lol.

 

[Supercharged111]

Master can leak internally and not make a mess. I've had that before, but it was always a gone pedal and not sometimes. Just stick with it, it's probably just 2 or 3 piddly **** issues making the truck feel like a POS.

 

[big_mike]

When my booster crapped out the pedal would go almost to the floor instantly then get stiff at the end of travel. I could hear air escaping when when I hit the brakes, I'm guessing that meant complete bladder failure on it. It never effected how my truck ran though, just braking. Wonder if it was cause it was a internal failure not in the hose or hose connection??

 

[MouthForWar]

Well I just got back into town, ran her on a short errand, she died again and now wont stay running more than ten seconds and stumbles something awful, way worse than before, after about the first 3 seconds.

Went ahead and just had her towed to the shop to have them take a fresh look at it and check out the fuel system since my pressure tester isnt here yet.

I guess we'll see.

On the bright side the brakes haven't failed again. Lol.

 

[df2x4]

I'm betting on a massive vacuum leak somewhere.

 

[okiemudslinger]

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?

mine was doing that and replace the whole distributor and fixed problem

 

[cviola2005]

I say ignition module. They can fail slowly, usually when hot. They can also fail on the low rpm side and not the high rpm side.

 

[chipskittles]

I say ignition module. They can fail slowly, usually when hot. They can also fail on the low rpm side and not the high rpm side.

distributors do seem to be dying a lot around here lately, might be on to something...