idle surge

[notopherc]

I have a 1980 1ton pickup. The engine idle surges up and down. It has a fuel injected carberatur. It belonged to my dad who has passed away. He was an awesome mechanic but I am not. Do not know where to start.

[J-Mech]

Originally Posted by notopherc

I have a 1980 1ton pickup. The engine idle surges up and down. It has a fuel injected carberatur. It belonged to my dad who has passed away. He was an awesome mechanic but I am not. Do not know where to start.

Fisrst of all you have a carburated engine. You can't have both carburated and fuel injected

Does it surge
-Fast? or slow?
-Only cold?, only hot?, always?

[notopherc]

It surges always, cold and hot, fast and slow. The year model is 1989 not 1980.

[J-Mech]

Got it that helps a ton. Ok is the A.C. off? You could also have a vacuum leak. I need to know if when it revs up and down if it immediatly goes from one extreme to the other or if it gradually revs up and down. Does it do it in gear?

[2000CAYukon]

I just fixed a surging idle on my 90 K1500. Turns out the vacuum hose from the MAP to the TBI would not hold a vacuum. The glue on one of the elbows was liquid and I replaced it with a piece of vacuum hose. A leaking MAP can also cause a surge.

//2000CAYukon

[notopherc]

I replaced the EGR Valve. The old valve appeared to hold a vacum upon testing but the gasket was in bad shape. It had black marks from exhaust leaking by. After replacing both with new equipment the truck runs like new. Thanks to everyone for their input. It help rule out potential problems.