Well, This one has got me stumped. I have searched all over the internet and still can not pin down what my problem(s) is/are.

Specs on the car:

DOHC ZC, swapped into a std 1988 HB. ECU (PG7) throws a code 1.

I have had this engine in my car for about a year and have had very few problems with it. About 2 months ago I had a weird problem where my car just died as I was getting off the freeway from a 200 mile drive. It wouldn't start and I had to get it towed home. I dialed in the problem to the Main relay, and a blown under the dash #14 fuse. Replaced the relay, replaced the fuse, no more problems with not starting.

Then came my idle problem. The car will run just dandy then at a stop light every now and then the idle will drop down to where the car sounds like it wants to die. I usually just keep my foot on the break and gas to keep it from dying at any given stop light.

So in attempt to fix that problem I ran seafoam and bled the coolant system. No luck. So then I decided to start my trouble shooting. I remember that the car has the fan wired to always on, and that it gets no heat in the cabin. I also noticed the temp gauge stays at about 1/4 from the C.

So I thought to my self if its not warming up, the thermostat isn't opening and my bleeding of the system was useless. So today I went to rewire my fan the correct way and see if I could fix things.

I got the fan wired up the correct way and took my car for a drive. The temp gauge still showed it at about 1/4 the way up so I decided to go on a 10 mile freeway drive. The temp gauge dropped down to the Cold line while I was on the freeway. I stopped for in n out and while I was waiting in the drive through the temp gauge slowly went up to where it should be. Then the idle started going up and down up and down. I have always bled the engine and that problem goes away so I figured it was a good thing.

Got food and got back on the freeway and the temp dropped back down to the C line.


So I started to bleed out the system using the bleed valve and It didn't seem to be getting me any where after about 30 minutes. The fan never kicked on, but I did feel the bottom radiator hose get hot so I am pretty sure the thermostat is opening. I then decided another technique may be more beneficial so I took the radiator cap off and pumped all the hoses until all the big bubbles seemed to be out of the system. Turned the car on and watched the tiny bubbles come out the top of the radiator. I finally felt the heater core outlet hose getting hot and continued to pump as the car was running to get as many bubbles out as I could. Finally I had to call it a night. The Idle on the way back home was fine but my heat still isn't that hot and as I drive my car the temp gauge goes back down to the 1/4 way up from the cold line. I pulled in my drive way and it did its normal thing it does at the stop light where the idle sinks to about 200 rpm. So basically I have gotten no where although my heat semi works now.

Any ideas what could be causing this problem? Is there still a chance I have air in my cooling system or should I start looking into other things.

Cliffs:
Idle sinks to about 200rpm at stop lights
Car idles at Normal Temp but when driving drops to the Cold line.

 

Well what you are saying about the idle at stoplights is when the engine reaches operating temp if the car wants to die then it's probably your IACV (idle air control valve). It could just be dirty or it may need to be replaced.