idle issues cold start

[awzer2]

i have a 1990 gst with a rebuilt head .
It idles at 1500 on cold start .
then drops to 1000 rpm. is this normal?
my car is constantly running very cold below first white line.
i get like 16 mpg .
none of the four vacuums on top left of the throttle body are connected to their corresponding lines. so i plugged them.

would the vaccum lines not being connected cause high idle?
i heard this was a "cheap mod" that resulted in more full usage and pushed up the boost while not having the boost solenoid t'd into the intake vacuum.

is this all normal?
the car has headers, a full straight pipe and thats it. as far as i know.
should it sound like a truck?
it sounds like it has cams installed.
the guy i bought it from had no knowledge of these cars.
he just used it for work.

what kind of hp am i getting with the straight pipe and headers?
can i get an "around the ball park" estimate?

 

[mb3000]

Yes, cold start idle should be higher than a warm idle. Pressure test to make sure you don't have any vac leaks. You say your car is running very cold below first white line, check your thermostat.

 

[awzer2]

Yes, cold start idle should be higher than a warm idle. Pressure test to make sure you don't have any vac leaks. You say your car is running very cold below first white line, check your thermostat.

the thermostat clip is pretty badly damaged the wires are showing through the 20 yr old wire cover. that's probably why.
what happens if the car runs too cold?

 

[9!'clipseDOHC]

The car idles higher when the engine is cold to help it get up to normal operating temp faster. That is the job of the FIAV (fast idle air valve) which is the lower portion of the throttle body which has the two coolant lines going to it. Once the car is warm you should be idling at 750 RPM's +/- 100 (so 650 - 850 RPM's). If you are higher or lower your ISC (idle speed controller) will be outside of its range and won't be able to keep your idle steady. You set your idle with the BISS (Base idle speed screw) as shown here: 1G BISS Adjustment

As far as your coolant temp, the gauge could be off, the temp sensor could be bad,the temp sensor wiring could be bad (very common), the thermostat could be bad, the coolant levels could be off, or there could be issues with the rest of the coolant system. In your case I would start with the gauge and wiring. The temp sensor for the stock dash gauge is the smaller sensor in the front of the thermostat housing that has a single wire going to it. The one with two wires going to it which is loccated right beside it is the actual coolant temp sensor which the ECU uses. Most likly those wires are hard, brittle, and broken. You should cut back in the harness to before the damaged area and solder in nwe wire. Make sure you use shrink wrap so there are no exposed or touching wires. For the ends, standard female spade connector fit perfectly on the sensor prongs.

In regards to your question about the vacuum lines on the throttle body, all of the vacuum lines on the throttle body are related to emissions control devices. It is ok to remove them as long as you block off the rest of the system and cap the lines on the throttle body to prevent boost and vacuum leaks. Here is the stock vacuum routing diagram if you are keeping it stock:

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And here is the diagram for if you want to block off the emissions system:

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Lastly your car is over 20 years old and over time vacuum lines crack, seals dry up, and parts start to leak. With that you lose performance, gas mileage, and drivability. I would seriously recommend doing a boost leak test and fixing any and all leaks regardless of how big or small they might be. Here is a guide on how to do a boost leak test: http://www.dsmtuners.com/forums/articles-turbo-system-intercooler/169435-boost-leak-test-how-boostpro-net-tester.html. You can even make your own tester for a few bucks worth of basic parts from home depot or any other home improvement store.

Hope this helps!