Midnight 85

I was scanning my '85 today to see if I could find out why the idle increases all by itself if I let off the brake, I realize it will come up some just because the car is rolling but it comes up over 400 rpm and will go along without me touching the accelerator. I found a code 24 which is the speed sensor so I figure I have that one solved. However, while I was scanning I also noticed the car was in open loop while idling. I could rev the engine up & hold it & it would eventually go into closed loop until I let off the gas again. It seems like the O2 sensor is cold but I have a heated one on the car because of headers. Apparently it is working since nothing else shows up wrong so what is your guess as to why it will not stay in closed loop?

toptechx6

Why do you assume the O2 heater is working? Your ECM cannot monitor the heater operation because the it was not equipped that way from the manufacturer.

Midnight 85

Good point, I plan on going out later when it cools down & see if it is getting power or if it just dead. When I re-read my first post I realized I goofed. (First time)

toptechx6

After you check for power at the sensor, check the heater circuit with an ohmmeter, if it is open that is likely the problem.

Midnight 85

Thanks, I'll do that.

Midnight 85

If I checked the sensor correctly I think it is bad. It has 3 wires, 2 white & 1 black. The black one is the signal wire. I put an ohmeter lead on each of the white wires and it went from infinity to 0.00. Shouldn't there be some resistance? I then put power to the one white wire & grounded the other and the sensor did start getting warm but it took some time and it never got too hot to hold. Unless I hear different, I am going to get a new sensor in the morning.

toptechx6

You are correct that there should be some resistance, I checked several spares and all tested between 7 and 16 ohms. I have to wonder what scale your meter was on, if the reading was truely zero ohms you would pop the fuse on the power side assuming your ground side connection for the heater circuit is good. Make sure you verify that you have a good ground to the heater circuit when you are checking it for power, good luck

John Robinson

Yesterday I had a problem with the car not restarting after it was run 6 miles in 99 degree heat and sat for 3 hours soaking up the heat under the hood and the sun on it. It gave me a service engine soon message and I got the paper clip out and had code 15, code 21, and code 23. After the car sat for a few min. I tried to start it and it started without showing the service engine soon. Drove it home and when I got here I checked the TPS voltage I had .63 closed throttle and 4.1 WOT. This morning I again checked it cold and got .52 closed throttle and 3.99 WOT. From what the manual says I should have 5 volts WOT. Since the codes are for a lean condition could this lower voltage in the TPS cause a lean condition? Do I need a new TPS? I have checked the circuit grounds and cleaned the frame grounds in the last 2 days. All the grounds checked good.

Midnight 85

I checked for power and it was good, I then pulled the O2 out and tested it on the bench, the dvm was in the lowest range but sitting here I can't remember what that range was. I am replacing the sensor today and I am moving it into the collector, I had it originally in the reducer just behind the collector. I believe the sensor was weak since it took it a while to even get warm. I did not test it with a torch, when I got the 0.00 reading I just quit for the night. Thanks for sticking with me on this.

Midnight 85

Fixed! The new o2 sensor did the trick. Thanks again for the help.

toptechx6

Good to hear, glad it did the trick.