Mr.Griz

Hey people, got a question! My 91 sierra startrs fine idle's perfect cold but as soon as you let it warm up it starts idling rough, never stalls or trips a trouble code. Today i unplugged the vacum line from the egr valve itself and the truck worked perfect, as soon as i plugged the vacum line that is still hooked to the solenoid it starts idiling rough again, the same when i hook it back to the egr. I havent tried pulling the line off the solenoid yet to see what happens that way. The egr valve does move when you push it with your hand.

Is there any other checks i can do to find out what actually is the problem, (egr valve or solenoid). Am i missing something here any help would be appreciated.

Thanks

horse482

Could be that there is carbon keeping the erg valve stuck open. You should be able to purchase one at any parts store, make sure that you take the casting # off your old one and have the parts store cross the # to insure that you get the correct egr valve. Also if the solenoid is broke and is constantly pulling a vacume on the egr valve. BTW, egr valves after market run about $50. Hope this helps.

2000CAYukon

You need a vacuum pump to test both of them.

EGR Valve: Ignition off, hook up a vacuum pump to the valve and apply vacuum (15 or 20 inches). It should hold the vacuum. If not, replace. Start engine, the vacuum should go to zero. If not, replace.

Solenoid: Ignition off, apply vacuum to TBI side. It should hold vacuum. If not, replace. Ignition on, engine off, jumper terminals A and B on the ALDL connector and you should see vacuum on the EGR side of the solenoid.

By the way, I have the 90 service manuals and just tested my EGR valve and solenoid on my 90 K1500. In my case, the solenoid would not hold vacuum so I replaced it.

//2000CAYukon

70GTORAG

Spray WD-40 into the diaphragm with engine running. If engine idles up, replace EGR. Also, if this is an original part, because it is a mechanical item with 15 years of use, replace it.