First off, I've got alot of info from this sit while building my car. I should introduce my baby that I have built from ground up (I did all the work myself). She's a 1957 Chevy 210 Sedan with a 350 TBI, 2004R overdrive transmission operated with a B&M sport shifter, narrowed 8.8 Explorer 3.73 posi rear, Denny's HD driveshaft, PRC's crossflow radiator with dual spals, hydroboost braking system with all stainless steel brake lines, 2 inch drop spindles, 4 wheel disc brakes, all stainless steel fuel lines, IDIDT chrome steering column with a APC sterring wheel, all Autometer gauges custom fitted to my cluster, front and rear seats from a Chrysler Sebring and 18" Boss 304 wheels. Paint is Daytona Metallic Blue, not done with her but here she is:


I did all the wire install and learned alot about TBI engines while doing it. I should say that the engine was basically new when I got it. It had about 50 miles on it when the 57 Nomad it was in was wrecked. It is built for a 1989 Chevy G10 van.
So on to the problem. It won't start without me barely cracking the throttle and it won't idle up when turning the wheel (it has power steering) or hitting the brake pedal or shifting to drive, etc...So I've spent the last year working on the problem. Testing everything I can. When this all began I suspected the IAC valve. After pulling it I saw it was cracked at the base but was clean as if it was new. There is no carbon build up what so ever in this engine, looks brand new.
I replaced the IAC valve and it still reacts the same way. I have reset the IAC numerous times, tested the TPS (which is perfect), replaced the coolant sensor, etc. Everything that affects the IAC is working as should but the IAC is still not retracting upon startup or when it is suppose to increase idle.
One day I finally got tired of looking for the problem and took the car to a automotive computer specialty garage. When I went back to pick it up and they told me my timing was at about 14 degrees advance and I said that wasn't suppose to be and asked if the disconnected bypass wire on the distributor when the set the timing and they said yes and pointed to the wire that ran to my O2 sensor and we had to reset it, I observed all the readings on their hand held reader...the IAC steps were with the correct range. Actually everything was correct except the idle was a little low. We adjusted the idle screw a tad and I paid them. Got back in the car and the idle dropped so low it would barely run. I got home and readjusted the idle and that's the way she has been ever since. They did offer me a few comp hook up because they screwed up the timing.
Anyway here is what I need....

I want to know the voltage across A to B and C to D - right now I am getting 10.5 across A to B but have to reverse leads from (C to D) to (D to C) to get a positive 10.5. I'll have to verify hot pins on the plug with my wiring diagrams. If the wires are backwards on one side then I'm not sure if it would retract - wouldn't both sides always push out?

I would also like to know the resistance across the terminals on the IAC valve - just to make sure the IAC valve isn't shorted out.

My conclusion is that the problem is the IAC valve. My main reason is I can remove the IAC valve and push the pintle in and reinstall and the car starts absolutly perfect, idle is expected to be high but I only have to reach through the window and turn the key. Once the car is turned off it resets the IAC and closes it all the way. The start and idle issue returns and I can not start it through the window.

This topic has been discussed alot on here but I could not find specific information to verify a shorted IAC or incorrect wiring from ECM to IAC.

So, I'm looking for voltage across the 4 prong plug with key on as well as the resistance on the IAC itself.

 

There's some wiring harness and voltage checks at website below. You'll have to register to download them, but I know the 7747 are there. I put them there.
http://www.eagle-mark.com/Forums/

 

I wired a 1995 TBI unit into a 1984 Vette. I finally got the wiring correct to make the IAC move correctly. Search a thread I started about 2 years ago for wiring advise.

 

Was it a Big Block IAC? Big Block IAC has 2 wires swapped in the IAC and must be changed when..... no... now that I think of it the change is in the wiring harness. I'm going to leave this so people think when they do the swap.

 

Yes a BB IAC and same on TB. Not sure if my color code on my 1984 harness are same on all GM harness as far as IAC. What I do know is the IAC itself had diff color code. Wires are considered A-B-C-D on IAC. I have wiring at home on paper notes. Regardless last post in my thread worked.

 

YES! Color codes are differant and same on some years BB and SB so you have to go by IAC position and wire to ECM location.

 

Well, I typed a bunch of info up and I got logged off while trying to post so I'll try it againl. Basically wiring a 350 TBI into a 57 Chevy was not the funnest thing I've done. The problem was the 57 ignition switch doesn't supply power to the aux side when in start and it doesn't have power to the start side when in aux position. Had to install some relays to maintain power to the aux side of the switch. The reason? because with out constant power to the aux side, I lost power to the ECM which powerd my injectors which meant no start. After that was finally figured out car start, runs and drives but the IAC is giving me problems.
Since the TBI was made for a 1989 G-10 van I tracked down the wiring diagram for the motor. The IAC wires are ltblue/white, ltblue/black and ltgreen/white, ltgreen/black. I just found out after looking back at the wiring diagram that I have been testing the voltage wrong. I went from A to B and C to D but the flow of the IAC is D to A and B to C. I believe I'll still get 10.5 volts but at least I will know the flow. Which is hot in a white black wiring setup?

 

I found this thread: https://www.thirdgen.org/forums/diy-...i-iac-7-a.html
may be helpfull
another:https://www.thirdgen.org/forums/tbi/...-yet-ohms.html
yet another: http://www.megamanual.com/ms2/IAC.htm#stepper

 

So I checked the IAC valve and got 52ohms across A/B and C/D. I believe that is good. I then pulled out the wiring harness diagram and verified the wires to the pin connector. The diagram showed them different than the connector. I switched the wires around but got nothing. I tried several different ways but am not sure if any where correct. I could get the pintle to move completely out and sometimes in and I belive sometimes it was doing both but no matter what I tried I could not get the IAC valve to open at startup. Hopefully you guys can help. Here is what I know
My ohms seem good on the IAC valve itself.
The IAC is new.
I get 10.5volts from the connector wires for both sides of the IAC.
The 89 G-10 wiring shows the blue/white wire to D pin and blue/black to A pin and green/white to B and green/black to C.
According to my readings I get ohms reading on the IAC from A to B and C to D which doesn't seem to fit the wiring diagram.
I am not understanding the test i should be performing.

Heres what I need to know.
If I push the pintle in, jumper A and B on the ALDA, attach blue/black to A and blue/white B, turn key on and if pintle moves out, can I assume the wiring is correct for out movement?
If I turn key off, disconnect blue/black and blue/white and connect blue/black to C and blue white to D, and the pintle moves in then can I assume replacing on the blues with the green on C and D and move blue back to A and B, that the wiring will be correct?
Am I confussing anyone besides myself?

 

Another question, the pinout at the ECM is the following
C3-ltgreen-blk 444
C4-ltgreen-white 443
C5-ltblue-white 441
C6-ltblue-blk 442

Which wires are high and which are lows and why can't it be determined which wire goes to what pin on the IAC if the wiring diagram is wire?