89 idle issues

[k9ulan]

I have an 89 Sierra, 5.7. auto,When I first got it it had very hi idle. I replaced base plate gasket nad idle air control valve. It ran fine for about a week. Now it idles rough , especially in drive with brake on. I have replace plugs, wires, cap and rotor, Fuel filter . No change..any advice appreciated.No service engine light and no vacume leaks that i can find..

[k9ulan]

Update:Changed tps , no change

[dogred]

Disconnect your egr and plug up the barb on the carb/tbi. I have this problem with my egr hooked up.

[Revredneck]

Sounds like your EGR valve is leaking. First unplug the vacuum line and see if that fixes it. If not, remove the EGR valve itself and see if there is debris around the pintle. You can make a simple block off by cutting a piece of pop can to fit the base of the EGR valve. It will turn on the Check Engine light, but it will get you going.
Good Luck and God Bless

[k9ulan]

Thanks for the replies, a little more info. I set the timing to 0 with the timing wire unhooked. Runs great, but, when driven it pngs and detonated terribly, so I have to retard the timing to get it to run ok, but still idles poorly. Is this still pointing to egr? all help appreciated..

[K15 Blazer Guy]

could also be the engine running too cold and trying to warm up.
someone said these trucks are engineered to run at 210 so they burn cleaner....
check how your plugs are burning too. that'll say it right there