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EFI Question


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Have a 1991 V8 3.5 EFI discovery. The problem I am having (and have been for some time) is that I can't seem to get the tickover revs correct. It tends to tickover at about 1100 rpm instead of 7-800 rpm. I have adjusted the allen bolt on top of the plenum (idle air valve ?) which has brought it down some but not enough. The screw has now been turned fully clockwise (I think) which did drop the tickover revs but not enough to bring iot down to the 7-800 rpm it should be. Sometimes just after starting it will settle to about 750 rpm but as soon as I use thethrotle it goes up again. Any clues ?



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Provided that you have no air leaks on the inlet side, then it looks like the IAC is probably gummed up and sticking.

As it’s a 91 I am assuming it will be a hot wire ………. The IAC (Idle Air Control) is a stepper motor on the rear of the plenum ………. Remove it and carefully give it a clean …… but don’t be too rough as they are expensive …….. usually a good clean will do the trick.

However, as I said before……… check for air leaks on the vacuum side as often a small split in a pipe will give the same symptoms ;)


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