1987 5.7L TBI stalls a lot...

[Ecnerwal]

Engine is 5.7L V8 TBI (or 350)

Stalling a great deal. More hot than cold (otherwise the temp sensor mentioned in another thread seemed like a great possibilty). More in reverse than forward, though it happens in both - runs fine while running, but when slacked off to come to a stop it frequently (but not always) dies. If I keep a foot on the gas and fight it with the brake to stop it stays running. Seems essentially like the idle speed needs to come up, but with the computer controlling it I can't see a place to adjust that; I also can't see that it should have changed, and this used to work fine. I've been living with it for long enough that I can't recall for sure if it was sudden or gradual in onset - I'd guess gradual.

I've asked about it when having other things serviced, but never gotten a reason for it (despite getting comments that "it stalls a lot", as if I hadn't noticed, and asked them for a diagnosis or repair...)

1987 crew cab 1 ton 4wd (single rears). 131000 miles - recently made a 2000 mile trip without major trouble (did blow the same air injection check valve I replaced 3 months ago when the original one blew), and only used about a quart of oil, despite a constant slow drip which I have not tracked down the source of. Makes a small amount of blue smoke when starting these days, but only for a few seconds. Have not checked compression, etc... TH400 tranny.

Despite being in the rust belt, the price of new trucks is prohibitive, and I'd like to keep this one functional for a while longer. I've got a few other questions, but I'll separate them out into other threads.

[luxman2173]

my truck did the same thing once before.i changed the temperature sensor and the map sensor and it worked fine after that.

[Jason Spears]

I checked out your problem in my GM service manual. They suggest checking:

Ignition timing.
P/N switch circuit.
Leaking injectors (causes low fuel pressure)
or injectors running too rich or too lean.

Would you consider the idle to be rough when it is hot? If so there is a bunch of stuff to check.

Including:

System voltage. A lot of the sensors don't work correctly if the voltage is low.
EGR on while idleing.
IAC valve
MAP sensor
Check the oxygen sensor for a white coating

Are there any codes stored in the computer? You can ceck these by putting the vehicle in diagnostic mode. Look at the connector under the dash, stick a paper clip between the "A" and "B" terminal, the two in the top right hand corner. Turn the key to the run position and the codes will flash on the service engine soon light. It will flash code twelve three times and then any other codes stored in the memory.

Hope this info helps.

Jason

[Ecnerwal]

Tried the jumper trick - Just endless blink;blink-blink, which I gather is 12 endlessly repeating, indicating that the systems works, and has no stored codes. SES light comes on when it stalls, but is not on otherwise.

I don't see obvious signs of injector leaks.

I don't think it's "rough" when hot - it's just more prone to stop entirely. But I'm not the world's greatest mechanic.

I'll try to look at some of the other stuff shortly.

Voltage was 14 or so when running.

If all screwed connections came apart without breaking, I'd be a lot more thrilled about doing my own mechanical work. If I could find a truly good mecahnic, I'd be a lot more thrilled about paying for it. As it is, I keep muddling on...

[Captkaos]

It sounds like (as above stated) the IAC or the MAP sensor is bad.

[Grim Reaper]

EGR. It's stick on when Idleing. EGR does not fuction till fully warm and doesn't activate till over 1200 RPM.

What happens is once it activates it's sticking open. I had a poor idle issue that was complicated with a vacuum leak so I wasn't stalling BUT I did have the EGR on.

Quick test is just unplug the vac line to the actual EGR valve and drive it and see if it does it. You will get a light but it will run fine and compensate for testing. No problem happens then you have it narrowed down to a carboned up pintle in the valve OR the stupid control valve. In my case it was the control valve. I put a couple drops of air tool oil inot both port and still doing fine after close to a year. Nice cheap fix. Problem was I decided it was the valve and replaced it first LOL.

Those plastic lines are very brittle. Have some vac hose handy, your probably going to need it.

[Grim Reaper]

Ohh and the reason it's wors in Revers then first is revers is geared higher.