Well, I replaced the Oxygen sensor. I rebuilt the TBI to clean out all the crud. My 92 Chevy S-10 Blazer with 4.3L V-6 STILL WON'T IDLE!!!

I think it may be the Idle Air Control which seemed hard to move but the parts store is closed already.

Does anyone know how to test one of these buggers?

Edwin

 

If you pull it out and leave it plugged in, it ought to move when you turn the key on and off.

 

I have to wait for the sun to come up again. I got to late a start on this old thing.

Thanks

Edwin

 

Just for giggles try changing the vacuume hoses on the thing. In my limited experiance, replacing vacuume hoses is generally the cure all for a lot of little problems....
Unfortunatly it did nothing to cure my '87 suzuki samurai failing the smog test with high carbon monoxide (CO) levels during the driving test. Maximum allowable is 2.52% and mine is running 4.35%

 

I had a few cracked joints on the hoses. While replaceing them I found the PCV port was plugged on the TBI and given the amount of crud in general I decided to kit it. While I had it apart I noticed the idle air control was very hard to move by hand. I understand it's a stepper motor but I have no experience to be able to tell if it's supposed to be very hard to move or not. Hopefully it doesn't cost very much and its replacement will cure the problem. There are no codes in the computer to tell me anything. There WAS a code which indicated the oxygen sensor was defective but that $55.00 part didn't fix it either.

Thanks

Edwin

 

The stepper motor is very tough to move by hand. My friend Joe and I went through this same problem on his 93 full size Blazer w/ TBI 350. His problems were a very crappy idle, it ran cold, and got terrible mileage. We tried an idle air controler, the MAP sensor, and a few other things, none of which helped. Joe ended up taking it to a independent mechanic (niether one of us could figure this problem out). The mech pulled of the entire intake assembly and when he did found that the EGR valve had fallen apart and the valve dropped into the intake. Joe was lucky though the vlave never made it into the head. Any way, the EGR just free flowed exhaust into the engine like a very large vaccum leak. After replaceing the EGR valve the engine came back to life, got way better mileage and performance and ran at the proper temperatures and idled just fine.

I reccomend before throwing anymore parts at it to buy a vaccum guage and hook it up to your engine while its running. That will at least let you know if you have a vaccum/intake leak (which can give you all sorts of problems).

Heres a link to how to use a vaccum guage to diagnose a variety of engine problems. The gauge can be had at Sears for under $25 and comes with a variety of fitting and some vaccum hose to connect it.

http://www.obd-codes.com/howto/diagnoseengine.php

http://www.classictruckshop.com/club...ts/vac/uum.htm

 

Thanks for the info.

I took out the EGR valve and inspected it. It's fine so I went down and bought the IAC motor and it seems to have fixed the problem.



I wish you could buy better manuals at these parts stores. The ones they sell usually cover several years and models but none of the various subjects very well at all. If the info in my HAynes book was better I might have saved much time and money buying parts I didn't need. It didn't have word one about the IAC and didn't have anything on my particular TBI system either. Everything else is to general in nature to be of much use and is in the everybody already knows that category.


Thanks everyone for your help. Yo are all worth a whole shelf worth of books.

Edwin

 

Went for a drive to Sonic for a Junior Banana Split and it's dying at idle again! I'm at my wits end!!! I don't know where to look next. The computer doesn't show any codes, the EGR is fine, the IAC is new. The oxygen sensor is new. I just kitted the TBI and replaced the PCV valve and leaking hoses. I even disconnected the vacume line to the EGR to see if it was sucking in at idle. No help.

I think it's trade-in time. Anyone interested?

Edwin

 

Edwin,

Try the vacuum gauge. No point now in guessing and throwing more sensors at it. Disconnecting the EGR vac line won't accomplish much. My friends joe, his valve failed internally and free flowed exhaust, The ECM could not control it at all. If the EGR failed, it won't suck air via the vac line, it will take the exhaust gasses. The vac line is only there to make the valve open and close.

But do try out the vaccum gauge, I read more on it and it will tell you a lot more info than just a vacuum leak.

http://www.classictruckshop.com/club...ts/vac/uum.htm

 

I took the EGR valve completely off and inspected it. It's fine. I was just worried that the control for it was applying vacuum to it when it shouldn't.

I have a vacuum gauge so I'll stick it on tomorrow.

Thanks.

Edwin

 

Edwin,

Any update on this? Just wondering if you were able to finder your problem in that engine?

 

Nope! The vacuum gauge reads normal. I got an appointment for next Tuesday for an expert mechanic to put his computer on it and see what he can find.

I'll update here when I find out.

Thanks

Edwin

 

Dang, that is one tough nut to crack.

Thats both good and bad about the vaccum guage readings. Good that it indicates that there is nothing mechanically wrong with it, bad that it point you deeper into the electronics side of it.

Look forward to seeing what the mechanic finds out.

 

The Mechanic says he'll check it for $50 and then will rebate part of that if I have him fix it. I see the computers on Ebay for under $50 if that's the problem. According to what I've read, the computer reads the engine RPM then adjusts the idle air control to get the desired RPM. I've watched the solenoids on the TBI and when it falters the solenoids go wonky and don't provide enough fuel.

Before anyone says it, it's not a fuel pressure problem otherwise it would show at speed. It runs fine on the highway even at WOT.

But that gives me a thought. Could the computer be cutting off the fuel pump when it idles down? Anyone?

 

Fuel pump cutoff ? Not on an EFI GM engine. Fuel pump is controlled by a relay controled by the ECM. Its either on or off. The pump puts out somewhere around 50-70 PSI to the injectors. Can't remember if there is a return line to the tank or not. I think there is.

The computer sounds like its working normal. Joes blazer did the same thing, his ECM struggled to try to control the engine, and since it was operating out of its normal parameters the ECM would just get confused.

Edwin, was the vacuum reading normal when it would idle funny? What was the readings when it acts up?

I wonder if the EGR valve is opening when it shouldn't and flowing too much exahust into the engine at idle. I believe EGR valves are normally shut at idle and open up while driving.