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ISA questions

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I've done a search, no answer I need there :typing: .


First, what exactly does the ISA do? I have a 2.5 TBI, 4 speed, no P/S, no A/C. With all the other work done on the motor :brows: it runs fantastic, strong (for a 4 banger), smooth, doesn't burn any oil, BUT after it warms up it has a high idle speed. Vacuum hoses have all been checked and replaced :wrench: . The ISA plunger seems to be retracted (it will spring out when throttle is opened) and at closed throttle the cable bracket rides on/sits against the end of the plunger :hmm: .


I had the idea :smart: that IF it's function was to bump idle up with A/C on I could remove it or shim behind it so the throttle will close completely (plunger/bracket). Any second opinions? I'm getting decent mileage but would get even better if the idle wasn't so high.

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if it idles high AFTER it warms up it may be the O2 sensor. Until the engine warms up it runs on some preset info. Once it warms up it starts using all the sensors for info. You cannot remove/shim the IAC/ISA. It controls how much air is allowed in the throttle body tp mix with the fuel

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Oh ok, thanks maddzz, I guess I'll have to bite the bullet til next Friday and get another O2 sensor (it's probably all gunked up from PO's neglect, if the inside of exhaust is any indication). Oh BTW, the EGR seems to be ok, can open it by hand with no binding.


You see where I was thinking.....older injection/carb vehicles used a solenoid type thingy to "prop" the throttle when the A/C was turned on or when cold.


I'm still on a major learning curve here because up until I bought my Benz 5 years ago everything I owned has had a carb on it, fuel injection is a new thing to me. (we had my son's '54 Caddy running 10 minutes after the wrecker guy dropped it in the D/W when we bought it)

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