1991 Chev S-10 idling question

[brother chris]

I have a question about the idling. 1991 Chev S-10 4X4 Automatic 4.3 liter.
My truck idles fine for the first 10 minutes (I guess while it warms up), then it all of a sudden revs up real fast and stays like that. Around 3500rpm! If I tap the gas pedal, it bogs down and dies. Then it won't start. If I wait an hour or so; sometimes sooner, it will start up and I go through the same thing.
Short history of the truck. I've had it sitting for about a year and a half. I've used it when I needed to, but for the most part it has been sitting there. (because I needed to replace the transfer case, which is what I am doing now).
I put Sta-bil in the gas.
I started the truck every month or two and ran it for 15 minutes or so.
The last time I used the truck was 6 months ago. It ran fine. And I put Sta-bil in the gas 6 months ago as well. And I just put fresh high octane gas in it yesterday.
I know I probably cannot fix it myself and will most likely have to take it to a mechanic. I was just wondering if anyone might know why it would rev up so high. Is there something I can put in the gas, or ???
Any help or tips would be greatly appreciated.
Thanks,
B.C.

 

[Kenneth Brown]

Re: 1991 Chev S-10 idling question

Look around for a vaccum hose that might have rotted or been eaten through by a mouse. I have had a similiar condition on my wifes Montana and a mouse had chewed through the vaccum line to the map sensor.

 

[JCF350]

Re: 1991 Chev S-10 idling question

Should idle rough with a vacuum leak but check anyway. Sounds like the temp sensor is acting up or has a bad connection. Check the vacuum lines then take it to a mechanic who has a scanner that is able to read the data stream between the sensors and the PCM, not every sensor malfunction will show a fault code.

 

[dolluper]

Re: 1991 Chev S-10 idling question

Hi there BC first grab the codes if any paper clip between the A +B connector which is the top far right last two ,check engine light will flash with the key just turned on not to start>>>> one flash pause 2 flashes = code 12 it should give you that at least 3 times then another codes if not 12 again....anyways if you don't get any other code take your battery out and re charge it go from there and let us know
Turn ignition switch to OFF position
Locate Data Link Connector (DLC), see image below.
Jumper the A&B terminals(a paper clip or a jumper wire work ok)
Turn Ignition switch to ON position.
Count the flashes on the "CHECK ENGINE" or "SERVICE ENGINE" light.
FLASH, pause, FLASH, FLASH = code 12
NOTE: Some 94 & 95 models do not have the B terminal. In which case a scanner is required.
NOTE: Some 94 & 95 models that DO have the A & B terminals still require a scanner.
All vehicles after 96 are OBDII,and require a scanner to access them.

12 Pin DLC
A - Ground F - TCC
B - Test Terminal G - Fuel Pump
C - Air Injection H - Brake Sense Speed Input
E - Serial Data M - Serial Data

 

[brother chris]

Re: 1991 Chev S-10 idling question

Thanks guys, for the tips.
All the hoses are fine. I'll try checking the codes tonight or tomorrow when I get some more time.

 

[Windykid]

Re: 1991 Chev S-10 idling question

You probably need to look at the Idle Air Control.(IAC)

 

[thefairlaneman]

Re: 1991 Chev S-10 idling question

You probably need to look at the Idle Air Control.(IAC)

Yes I agree. I have had several ford products that did then same thing and the IAC be the problem. Next I would check the TPS (trottle position sensor)

 

[dolluper]

Re: 1991 Chev S-10 idling question

Errrr did you find a paper clip yet?????

 

[brother chris]

Re: 1991 Chev S-10 idling question

No, sorry, I have not done the paper clip check yet. Every time I come home it is dark. I will give it a shot on Sunday when I am not working. I will definitely post what I find out.
See, work always get in the way!!!
Brother Chris.

 

[island boy]

Re: 1991 Chev S-10 idling question

If you try getting codes and all other advice posted above try replacing the MAF it was doing the same thing to my friends 96 comaro and he tried tons of stuff and finaly he replaced the MAF and it cured the proble. JUst a thought hope it helps.

 

[JCF350]

Re: 1991 Chev S-10 idling question

His vehicle doesn't have a MAF sensor.

All your buddy had to was clean the hot wire/resistor on his though, use a q-tip and rubbing alcohol. It was obviously still working as the data from it was still changing with the change of air flow, it was still within parameters but not reading correctly. If someone had looked at the data stream (something you don't get with a code reader) during testing it would have been obvious that it wasn't reading correctly.

One reason to take it to a pro who knows what he is doing.

 

[brother chris]

Re: 1991 Chev S-10 idling question

I finally managed to get a battery that was good.
It read. Flash, pause, flash flash.
Now what?

Thanks,
B.C.

 

[Coors]

Re: 1991 Chev S-10 idling question

I don't have access to my books, but google s-10 codes.

 

[JCF350]

Re: 1991 Chev S-10 idling question

I finally managed to get a battery that was good.
It read. Flash, pause, flash flash.
Now what?

Thanks,
B.C.

Code 12 = Diagnostic mode/pass code no faults found

GM codes will flash 3 times then will move on to the next code if there are any.

Since you changed the battery you reset the computer in the truck. If it is still exhibiting the same problem you need to get to someone who has a scanner that can read the data stream. Like I said earlier, not all sensor malfunctions will set a trouble code.

 

[JCF350]

Re: 1991 Chev S-10 idling question

BTW what is the eighth digit of your VIN#

 

[dolluper]

Re: 1991 Chev S-10 idling question

Oh carp hope you pulled the codes BEFORE you changed the battery>>> how does it run now anyways... same or did it change with the new battery... the flash pause flash flash is code 12 it will do code 12 three TIMEs then any other stored codes 3 times also when done it goes back to code 12 three times....Hope you didn't do the cart before the horse,ifin you did you will probably have to start and run it a few times before it will throw another code or until the light comes on ...then you can get the code If it doesn't throw any codes or the light doesn't come on Check it as if it doesn't have a computer

 

[brother chris]

Re: 1991 Chev S-10 idling question

The battery that was in the truck; I used it for something else, along time ago. I just took another battery that I had and threw it in the truck.
No, it does not run any better. Now it is hard to start. It will start, but unless I rev the crap out of it, it will stutter and die.
I saw a code reader at an Auto parts store for $40, so I might just go buy that.
But are you telling me that since I changed the battery, the codes will not read properly? Am I going to do this in vain if I go and buy the code reader. Is it going to tell me the wrong codes cause I changed the battery?
Am I better off having a mobile mechanic come over or tow it to a shop and have them check it out? I would like to figure it out myself and save some cash, but if I have to take it to a mechanic I will.
Thanks for the help.
B.C.

 

[Coors]

Re: 1991 Chev S-10 idling question

some codes are hard, they store even if battery disconnected- takes a scanner to erase.
A $40 scanner is no good; the proper ones are over $140

 

[JCF350]

Re: 1991 Chev S-10 idling question

I saw a code reader at an Auto parts store for $40, so I might just go buy that.

Make sure this is the right code reader. You need a GM specific one for your truck and not an OBD II reader.

But are you telling me that since I changed the battery, the codes will not read properly? Am I going to do this in vain if I go and buy the code reader. Is it going to tell me the wrong codes cause I changed the battery?

By disconnecting the battery what you did was erase the the codes that were in the vehicle (takes 10 seconds for a GM vehicle of that year) as your year vehicle only stores them in volatile memory . This will erase all the codes and resets the idle strategy in the computer making it not idle correctly (it'll take a few stops and starts for idle strategy to reset).

Am I better off having a mobile mechanic come over or tow it to a shop and have them check it out? I would like to figure it out myself and save some cash, but if I have to take it to a mechanic I will.
Thanks for the help.
B.C.

It's sounding like this would be the best thing for you to do. Most times inexperienced people start fiddling with computer controlled cars they end up replacing a lot of unnecessary parts and this can get expensive rather quickly. Labor rates are not that high when compared to parts prices.

 

[dolluper]

Re: 1991 Chev S-10 idling question

You don't need a reader use the paper clip {much cheaper}LOL...So your light doesn't come on ,no codes except 12,runs bad won't idle,have to keep feathering the gas to keep it running.....right so far? Borrow a fuel pressure tester at Canadian Tire and test the fuel pressure {fuel pump} and use a volt meter at the battery to check how many volts it's putting out when running ,should be around 14 if the charging system is good Let us know how this turns out ......My server is in and out these days until Wednesday then I will be back steady