Chasing 87' TBI idle problem. Included service code

[chevymotocross]

My truck, with the 305 tbi has been having an odd stalling problem. When first started in the day, the truck idles like poo. If I turn the a/c on and put it in gear, it will stall. Once it warms up, it idles good, but if you put the a/c on, and you aren't actually moving, it will stumble and stall.

I checked the IAC valve and passage. It is clean. The Coolant Temp Sensor was replaced last year since I suspected it was that, no luck. I checked for the codes it was giving and I get 3 flashes which indicates a Code 13: Oxygen Sensor issues?

The SES light goes away once the truck is restarted. Or, if it is about to die and I put it in neutral, the light will also go away.

Anyone have any input on this?

[stsalvage]

Ya i have a 1987 1/2 ton short bed fleet side it has to be one of the bastard child's i ever seen mine had a 305 but it was changed to a 350 I changed all the modulus and did every thing you not done net even changed the Cat and still have the problem I mechanic told me there is a ghost code that you can get a reader for sence that is kinda the first computer controlled fuel injected truck it had more bugs then your bed you sleep on.I'm at my last hope i was told i need to get a new computer box for it and Pray I gave up on it and now it just sits mine has the 350 now with the factory 700R4 no pwer windows no power door locks but it has every thing else.But I was told the throttle bare in the throttle body if it get worn or lose it will let air in and that will affect the Idle so take off your throttle body and grap hold of the bare with the flap and pull up or down and see if your brass shim in the body is lose if so 3 ways to Fix it order a new one for 700.00 or get lucky on ebay for a new one for 400.00 i think they make a rebuild kit for it But you have to hone out the body Put the brass sleeve in and put a bigger bare in and they only last for a little while that part was made to fail that why they only used it for 4 years 1987-88-89-90 then they went to fuel injected rail its a bad year to try and fight it6 it will cost you money to stay on top of it Check with your local Smog shop to see if they have any after market mod's they will allow you to use to make the truck pass somg if not you mi8ght have to go up to the 1993 computer and fuel injected system and wiring harness

[SS Delux]

I had pretty much the exact problems you had but I dont have a/c, and mine is stick shift 4.3L V6. I replaced all sorts of things and it would still stall. The code you are giving chevymotocross, is incomplete. The way you get your codes out of the computer is to use a wire or paperclip between the two terminals of the computer plug under the dash (pics to come). Once you have your codes you can look up what exactly is wrong. Now for the stalling problem and how I fixed it. It stalled on me one day and I pulled the code, wich told me it was the HEI Module. This is after I got a code for the MAP sensor and it had been replaced. I went to autozone and bought one as well as a MSD coil. Both were put on and it has never stalled since, not to mention the better burn in combustion. Make sure if you replace the HEI you use the supplied di-electric gel. The Hei unit is under the distributor.
For stsalvage, since you swapped out the 305 for the 350 you might need to get a 350 piggyback IC chip that you replace in the main computer of the truck. It is above the glove box and under a cover plate held on with one or two screws depending on your computer.
Good luck guys .... Aaron

[munger]

dude just switch to carb and drive it

[chevymotocross]

SS Delux, you are correct, I was reading the flashes wrong. It's not a code 13, it is a code 33 which would indicate MAP sensor issues.

I inserted the paper clip in terminals A and B. Turned ignition on. It flashed once, pause, 2 flashes which indicated the code 12 diagnostic mode. It did this 3 times. Then, it flashed 3 times quickly, pause, and then 3 times quickly again. It repeated this a few times and this was the only code found.

Thing is, I think it only stored this code because when it's about to die, running like poo, it is making low vacuum which triggers the light. It stalls, restart the engine and light is off because it idles fine again. I can see the MAP sensor being bad if it always idled poorly like that, but it only happens with the A/C on, in gear, not moving.

Is there any way to test a MAP sensor w/o simply replacing it? Seems from a few of your experiences, the ECM doesn't accurately point you to the actual cause of running like poo.