1990 suburban with high idle ?

[sidewinder]

Well,I tried all the diff sensors and checked all things noted with no luck.I decided to take it into a shop and have them hook it up to there computer.It came up with no pulse to IAC.They say this means it needs a new computer.I have located a few at the local salvage yards.Is this a plug and play type of swap or is there more to it?TIA

 

[Leper]

You need to look at your distributor very close. This just happened to mine. I was having the same problem, until it died. The piece inside the dist came apart. I dont know what to call it.I had noticed a hairline crack before, today when I looked, I pulled some pieces off of it. It hase some windings on it,kinda like an alt. winding. I believe it sends the pulse signal to the ecu. Anyway, as it starts to go bad, it advances the timing giving the higher idle.

 

[sidewinder]

I will give that a check.This part is under/inside the dist. cap?If so was it removeable with out pulling the dist.?Thanks for the info.

 

[muddbudd72]

i just had the same problem with my 90 blazer. my pcv was bad. changed it and now idles fine. the pcv wasn't that old.

 

[Leper]

I will give that a check.This part is under/inside the dist. cap?If so was it removeable with out pulling the dist.?Thanks for the info.

Yup, just take the cap off.

 

[BXwildshot]

DO you have cruise control? I had the same problem it turned out the linkage for the cruise control was too short and the throttle would not settle all the way down. I found this strange since noone ever had touched it. Hope this helps.

 

[sidewinder]

The pcv has been changed and the cruise was also checked with no change to the problem.I will be checking the dist. on sat. morning.Thanks

 

[Canadianbuilder]

I`m not sure if you got your idle problem solved or not but concerning your question about swapping ecm`s,yes it is plug and play.They are located behind the glovebox and on the 87 pickups and 87-91 blazer and subs they can be removed by undoing the bolt that holds the strap around the ecm.The bolt head is sometimes hidden behind the wiring harness as it`s tie wrapped there.Trucks without A/C are easier to get out but the ones with A/c just require some forcefull wiggling to get them out and in.
I went through the same problem you have(idle too high) on my 89 burb.In my case though I had swapped a 305 into a truck that originally had a 350.The 350 ecm caused the 305 to idle too high.I put in a 305 ecm from an 88 extended cab I have and the idle is perfect now.
If you don`t know the history of your truck you might want to double check what size engine it has.The previous owner may have changed the engine.Just a thought .