Got FI problems with my Chevy go getter

David M. Lyon

Subscriber
The pintle on the Idle Air control valve will not move if the computer can't find an initial reference point to know how many steps out to open it. It has to be manually moved to the extended (out) position, reinstalled, and once the engine starts the computer can adjust the pintle out the proper number of "steps" to maintain the correct fuel/air mix. If it is already open when you install it, the computer is "lost" and doesn't know which way to adjust it. You'll have to wiggle the pintle to get it to walk out of the ratchet enough to seal off on the throttle body seat. :brows:
 

Doug Tallman

Subscriber
All the terminals are dim all the time, no matter if it is jumped or not? Thanks
Does the check engine light flash code 12 with the key on/eng off and the A&B jumpered. If not, follow that troubleshooting tree first. You may have a power or ground problem or you have a computer going south. The light should change state at the IAC connector. The computer starts with the pintle backed out every time and shuts it as necessary. Some systems reset after the computer goes to closed loop and then shut off. Some systems have to see 35 MPH before they reset. The throtle body base gasket was prone to fail on these but it sounds like you have already covered that.
 

Avery22x36

New member
OK, everything checked out on the hand held computer reader again and I jumped A and B, I thought I was in the clear because I counted 12 flashes and then as I was unhooking them it started flashing again, I lost count at 43 flashes? Anyone got any ideas? Thanks
 

Avery22x36

New member
Bought a new complete TBI, bought another couple hundred bucks worth of sensors, just about everything is new but the wire harness and computer and its no better. Gaskets on intake are good and no vacuum leaks. Almost a grand in it now and no better. Talked to every shop around and they got nothing, everyone's readers says systems running fine????
 

C-Wade7

Member
Did you replace the coolant temp sender for the ecm? If it goes open it thinks the temp is -40 and it will run super rich until it floods out sometimes. The amount of fuel spray from the injectors will be high like a solid stream umbrella. It can cause some weird stuff.
 

Avery22x36

New member
Yea, one of the pro mechanics told me that sensor would be the #1 thing after a V leak so I replaced it and cleaned the wire connection.
 

Power

Active member
Well, as I said in post 8, stop throwing parts at it. Cost you lots to maybe eventually solve problem.
I do all the simple cheap stuff first.

Are you positive you got all the parts back right, with no air leaks?
The throttle body base gasket will "suck in" and leak if it is not installed right.

Stuck EGR valve can increase idle some.
Stuck PCV valve can too, as can any leaking vacuum hoses or accessories. Got power brakes? is the booster leaking?
Disconnect and plug all vacuum hoses and start it (do not test drive it this way).

There is one other thing - On some models, the throttle plates were coated with a black plastic on the leading edges. That was so they would not have to machine plates for close fit. If wrong cleaner is used, it will dissolve the plastic and there will be a gap, like the throttle is part way open.
 

Avery22x36

New member
I replaced all that stuff, there was no plastic on it, just shiney aluminum when I took the thing off. I have plugged all lines and tried it. With every single port on the intake and TB closed including the power brake line, it still did the same. I have sprayed around the base (multiple gaskets) and around the intake to see if I could detect even a faster pick up but nothing. Butterfly is at the most closed position possible. Of course the new TBI came with all the parts on it so that make a 3rd set of those things and still the same. Have tried multiple code readers and all of them say system is operating normal?????
 

J.B. Castagnos

Active member
Sounds like you can't afford to save any more money. I told you to see if the idle air motor was seated or backed in. If backed in the air will be going through the idle by pass port at the back of the throttle body, kind of hard to plug because of it's irregular shape, but a rag tucked in with a screw driver should slow it down. I can get you a wiring diagram, you'll have to check continuity from the computer to the idle motor, 4 wires, if they are good I would try a used computer, bought one for a 94 with transmission problems, $45 used, solved the problem. All of the parts you changed could have been tested, if they are good, a new is no better.
 

Power

Active member
I have sprayed around the base (multiple gaskets) and around the intake to see if I could detect even a faster pick up but nothing. Butterfly is at the most closed position possible. Have tried multiple code readers and all of them say system is operating normal?????
It will say normal. That is a 15 year old system, they were not as sophisticated as today.

I do it different - I use a pump oil can with heavy oil, like gear oil and go over everything. If there is a leak, heavy oil temporarily seals it, and I know where it is. Then I clean oil off - don't want to go on the road with oil on engine, could start to smoke or fire.
 

Avery22x36

New member
If you could get me that diagram I would be very grateful. carriagebuilder@hotmail.com. I tried to pug the hole several times and like you said, its not very easy to do and know 100% it is plugged. Holding the motor in my hand while someone turns on the ignition, sometimes I can see it retract as to open the passage (not every time) so I am thinking something is prompting the computer to open it? I can chase those wires down and check them, I have used a total of 4 air motors on it now and they all seem to act the same. I am an hour from town so just driving back and fourth for parts gets to be an issue. Thanks
 

Power

Active member
Well, like others said, most likely cause is air leak. second most likely coolant temp sensor. It takes a lot to bring engine to 3000 RPM. If you are positive no air leaks, then go on to the next free checks, before you go broke. Heck, you probably spent almost as much as she is worth on her.

At this point, I would look for electrical issue.
If testers show no codes, then most likely, the confuser and all parts are within their operating ranges. Now you look for something that would cause a sensor signal to come back to the computer at the fuel rich end of range.

A quick look at wiring harness to see if plastic has cracked and is brittle is worth it. Remember, signals range from 4-20 MA - just a break in insulation and some road dirt will conduct enough to throw signal off. I have not seen insulation failures on GM, tho.

While you are at it, check the computer ground. It usually goes right to engine block. Do not just look at it, take bolt out, sand clean block and terminal. put some dielectric grease on it and reassemble. I had one on a Ford that gave everyone fits. I figured out that mechanic did not put ground back under proper bolt when replacing manifold gasket. Cleaned everything up, put back where supposed to be, no more problems -still good when he sold car years later.

What I have seen in older vehicles is trouble at the connectors. Check out the big one for the computer. Make sure every terminal is clean, bright and tight. I use q-tips and toothpicks. Takes me a good hour to clean that one. I reassemble with dielectric grease so problem does not come back.

Disconnect the battery each time before you try it, to reset confuser.
If that don't solve issue, go after every one of the sensor connectors. Make sure they are all clean, bright and tight. Lightly lube with dielectric grease. Loose? that is what pliers are for, isn't it?

Do not forget oxygen sensor connectors.

It takes me several hours to clean all those connectors and terminals. Have to go slow and careful so don't break anything. If plug is tight, I spray with silicone spray and let it sit while I do another one. NO WD40, no petroleum solvents. Connectors, wire insulation, and O ring seals do not like that stuff.

Cost- your time and a few cents of dielectric grease.
 

J.B. Castagnos

Active member
The idle motor has two windings, two of the wires run it out, the other two run it in. It generally backs out a little each time the key is turned on, if it can't run back in it will keep getting faster and faster. I mentioned earlier we have a simulator to run it in and out, this eliminates all the other problems if you can slow it down. I'll get the diagrams for you, check out the circuits.
 

Avery22x36

New member
I took the softest rag I could find and it appears that it significantly slows it down, its not really slow enough to put in gear but its not just screaming now. All I can figure is its pulling some air through the rag?
 

J.B. Castagnos

Active member
If it's slowing down it's telling you it's a problem in the idle air system. If the computer were controlling it, it would have the idle air motor shut and it would make no difference. I have the diagrams printed, will have to take them home and scan them.
 

J.B. Castagnos

Active member
Here's the diagrams, wires to the iac motor are light blue and white, light blue and black for one circuit, light green and white, light green and black for the other circuit. They are on the 32 socket connector on the pcm, row C, # 6-9. Row C will have a pink/black at the top, dark blue at the bottom. Unplug the connector and check for continuity across 6-7 and 8-9, should be about the same, just a guess maybe 20 ohms. Open, a broken wire, check individually to the IAC to see which one, short, unplug the IAC and see if it goes away. Check for short to ground, should be open. If everything checks OK try plugging it back in and see if it works, could have been a bad connection at the computer, if still bad try another computer. Go to carpart.com used parts, inter your info, you can do a local search, should find one under $50.
 

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Avery22x36

New member
Thanks, I will work in this in the morning, got side tracked with some tractor repair today. I appreciate your help.
 
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