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IAC Valve: Does it operate only at Fully-Open & Fully-Closed modes, or are there different positions ? 700 1985

posted by  ndesouza on  Mon Sep 20 22:35 CST 2004
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last visit: Sun Mar 18 15:14 CST 2012
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Hi Art,

Yes - I expect that is a possibility. Though the IAS wire is a bit shorter than the TPS extension, so it would be a stretch, but still - it could happen.

Opened up the computer, hoping I would be able to spot the obvious burnt component - but that double-sided printed-board was as clean as the day it was made. I was really impressed with the condition, considering it was 20 years old. Found 4 large transistors (3 on a large heat-sink, and 1 by itself), along with 2 smaller ones. Considering the amperage of the IAC, I suspect 2 of those large transistors are used to power it. Difficult to test the transistors on-board with a meter, and the problem is not serious enough to warrant desoldering to test them - especially since I dont have a spare on hand. So I ended up putting it back together and reconnecting it.

I've made a simple circuit with 2 LEDs - one green and one red, that I'm going to connect in parallel with the IAC so I know whether it is receiving an open & close signal. Lets see what I find out tomorrow.

Interestingly enough, while searching the archives - I found a post by someone named Vroom (see link below) where s/he seems to have the same idling problem, and isolated it to one of those 2 transistors in the ECU. Fixed it with a replacement transistor. Would love to contact Vroom, but unfortunately dont find a mention of the name anywhere else, so...

http://brickboard.com/FAQ/700-900/EngineFIComputer.htm#RepairingYourOwnECU

Thanks again for all the responses,

Noel






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