1. Home
  2. Automotive Technologies
  3. 87 firebird FI 5.0 305 thermostat / air bypass / low idle problem

87 firebird FI 5.0 305 thermostat / air bypass / low idle problem

whats up people.. i got an 87 5spd firebird with a 305. the car is new (to me), the first thing i noticed was the coolant temp gauge going way past the 260 "redline". so from what people tell me its a busted thermostat. The car ran fine for a while (a day or two), but it now seems to idle really low, it usually stalls if i dont rev it up a little when i fire it up. my understanding is that the air bypass valve is controlled mechanically by the thermostat, and that valve closes as the thermostat rises, which lowers the idle. so becase of the busted thermostat, the car idle so low that it stalls.. does this sound right?

i looked at the coolant, and it is a couple inches below the mark, but there still is coolant in the tank. is it possible that i just need more coolant/water?

if the problem is the thermostat, can anyone give me advice on how to change it? is it an easy fix?

any other suggestions?

sorry this is my first car TIA

Reply to
will taubin
Loading thread data ...

Will, Go to Autozone, get a thermostat, the shop manual for the car, antifreeze (check to see what type), and a new radiator cap (just incase). Service the cooling system as outlined in the manual. DO THIS NOW. Don't wreck your engine by over heating it. You want to change the oil and filter, fuel filters, air cleaner filter too while the hood's up. The Autozone people can pull all the parts for you. Get in the habit of basic service on these older cars and you'll be happy to know they'll run well for a long time. Cooling system and that oil change right now.

Reply to
Rich M

Your information is wrong. The thermostat does NOT control the idle speed in any way. The computer does. The computer reads the temperature from a sensor next to the t-stat. This is NOT the same sensor that reads the temperature for your dashboard. Thats right, 2 temp sensors. One has 2 wires on it, one has 1 wire. It is very possible the computer is getting the correct temperature and the dash an incorrect one. The dash temp sensor is in the left head between spark plugs 1 and 3 and has a green (I think) wire on it.

The computer does open and close the air bypass (called an IAC -- idle air control)electronicaly. The IAC is not adjustable, but may be plugged with carbon on such an old engine. Find it on the throttle body, it has 4 wires on it. Unplug it, unscrew it, look in the passage. If it is full of crud, clean it out with an aerosol carb cleaner. Don't try to adjust idle speed with the screw on the throttle body, you will put the TPS out of adjustment, and cause other problems.

I havent addressed your overheat because it could be anything from a defective sensor to a bad t-stat. T-stats are cheap, go put one in and see if that helps.

Reply to
Curly

An 87 Firebird doesn't have a temp sensor near the thermostat, the temp sensor is on the drivers side cylinder head. The sensor on the passenger side is the radiator fan switch. The temp sensor only has one wire on it.

You should look in your radiator (while it's cool) and see if there's coolant in the radiator. The tank only tells you if the tank has anything in it. If the gauge on your dash is always on 260, then chances are you don't have overheating. If you're not getting steam from under your hood at

260, then you're not overheating.. Things should be bubbling out of the overflow tank at 260.

-Bruce

Reply to
Bruce Chang

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.