20 Most Recent 1999 GMC Envoy - Page 7 Questions & Answers

What year is your Envoy ? Probably high speed relay .

Did you check power an grounds , fuse's . Basic Electricity for Service Techs Ohm law Current Flow Opens Shorts http://www.bbbind.com/free_tsb.html free wiring diagrams . How to Use Multimeter Beginner Crash Course

Do you have heat coming out of the heater after the thermostat opens? If you do and the truck is still over heating the head gasket could be blown and burning the antifreeze through the cylinders and thus would cause a rough idle. You may want to run a compression test on the truck. Just to be sure your assumption is correct that the head gasket is good. Have you felt the heater hose to make sure it is circulating through the heater and it is not plugged. Hope this helps.

When guages go crazy, look for the ignition switch to be the culprit, OR the stepper motor behind the tach is going out.

First check your coolant level, you may have a bad thermostat that may need to be replaced if you are not geting coolant flow you may also want to consider a coolant system flush I your vehical has not had one since new

What year ?

Get the system purged as there is a contaminant in the system freezing and blocking the pipes

Very well known problem on the I6 engine. It's your fuel regulator, right hand side of the plastic resonator on top. Really should be a recall issue, it's that common.

Take it to any Auto Zone ! They will run a scan for you - there is no charge for this !

Yup

The internal resistor may defective. It's easier to just replace it.

It is mounted on the radiator to sense it's temperature.

Look at the vacuum hose on the cruise control actuator. It may have gotten gummy or lost it's grip on a connector.

Shoot some penetrating oil or WD40 on the center hub of the wheel where it contacts the drum. Let it work for 15 or so minutes then wiggle the wheel off the brake drum