88 S-10 idle issues

[buffblazer]

I got the task of fixing an old farm truck that has been mexi abused to no end.

It has a throttle body 2.8 that runs but won't idle.

I first had an issue with a bad injector, replaced that. Then it would pulsate randomly even with the motor off, testing came to a new ECM.

Now the MAP sensor was replaced but unplugged so when I plugged it in. It would half attempt to idle but would die. If you tried to drive it. It falls on it's face and won't run. Unplug the sensor and it won't idle without putting your foot into it, but once you get the revs up it runs down the road great.

Tested the plug it's getting the proper voltage and reads right when running. I even replaced it again just to be sure and it did not change anything.

Tested the TPS and it is operating properly.

Next thing is for me to check the ECT sensor.

If that ends up being ok where do I go from there? Im running out if ideas.

 

[buffblazer]

Oh I completly forgot it has an IAC valve I will check that then report back.

Oh and it's a manual tranny

 

[buffblazer]

Alright the idle air valve was good, so I checked the gap on the plugs and they were way off. So I re-gaped the plugs and it now attempts to idle but still stumbles when trying to go down the road.

The under hood sticker is screwed up and I don't have a book, so does anyone know what the timing is suppose to be on a 88 2.8 V6?

Figured I would check there and then see

 

[496truck]

Most TBI and computer controlled distributor engines want 0* for base timing. Although set 2* BTDC may run a bit better.

You've ruled out vacuum leaks and the cap, rotor, and wires are good?

I just did some work on a TBI 4.3 truck. It was stalling, running rough, poor power. I did the full tune up on it. But the exhaust was falling off in several places and loud. The tune up helped but didn't solve all the issues. Told the owner I couldn't go any further till he fixed the exhaust. Sure enough he had the exhaust done and it runs perfect now.

I don't know the condition of your exhaust but it could be adding to the problems if it's falling off (you did say "mexi abused"), especially with that little computer controlled 2.8.

 

[buffblazer]

Is it 0 with the wire ESC hooked up or unhooked?

Cap and rotor have been replaced. Its firing on all 6

It will half ass idle when it's warm but cold it won't. And if you try and drive it, it won't even let you feather it.

Now if you I unhook the MAP sensor it won't idle but it will let you feather it and run down the road.

The exhaust doesent have any leaks as far as I can tell.

Anyone have any idea where the ESC wire is on an 88 s-10? It doesn't have the fire wall fuse box like the 88 full size trucks have so I looked everywhere but cannot locate it

 

[496truck]

Wire disconnected.

IIRC mine was inside the cab on the pass side, under the glove box area. Tan with black stripe one wire connector. Mine was a 4.3 but I bet that wire is the same (even my K5 has the same color wire). May also be located on the firewall under the hood on the pass side. I've worked on a bunch of those old TBIs and can't remember exactly where the connector is on the S10.

 

[buffblazer]

So update. If the vacuum line going from the front of the throttle body to the MAP sensor is unhooked it will idle perfect and will run down the road. Only issue is have to flutter the throttle to get up to speed, it won't let you stand on it or even partial throttle.

I know the MAP sensor wiring has the right amount of voltage to it and it's on Its second sensor so I would say my problem Is isolated to there but then again everything checks out

It's running 17 degrees on the timing. I believe I found the wire for the ESC but after unplugging it the motor sped up but did not change time so either that's the wrong wire or it wasent ever adjusting the timing in the first place.

I think I will just go get a book, was hoping not to have to drive the 40 miles to town but looks like I have no choice

 

[zombiyjay76]

I'm sure you checked, but how is the fuel pressure. And has this truck been sitting for a while (bad fuel?) Recently had idle issues with one of our brush trucks, went through every thing trying to figure out why it wouldn't idle and run right. Turned out to be bad fuel, the truck was running so bad it was getting fuel into the oil. Emptied and refilled the gas tank, changed oil, and a tune up, now it runs great.

 

[buffblazer]

Alright so truck will not idle when cold. Have not checked the temp sensor yet and have not got a book, any ideas what it could be while I wait to get my book?