I’ve got a problem with my car not getting hot enough to go in to closed loop and its idling rough. I had some codes and I cleared them. I had to replace my MAF sensor, the MAF relay and the burn off relay. My car runs good now with no codes stored in the computer or no new codes coming up after I made the repairs. I've also set the throttle position sensor to the factory setting of 0.55 Volts.

It won't get hot enough to go in to closed loop mode and it won't get hot enough to let the converter lock up so my fuel economy has went in the toilet. Anybody have an idea what the issue could be? I am also running the stock 195 degree thermostat and stock chip in my car. I’ve got a 1988 IROC L98/7004 drive train.

Sometimes after I drive on the freeway and get off and stop the temp will go up to around 220 degrees (it was running around this temperature before when it went in to closed loop mode) like it used to for a couple of min. When that happens the converter locks up in overdrive like it’s supposed to so I think the TCC and VSS are working properly. A couple of min later the temperature starts dropping and it goes back in to open loop mode.

Today I replaced the coolant temp sensor and the oxygen sensor. Now the car gets hot enough to go in to closed loop but its still idling very rough. Anybody have any ideas on what I should look at next?

 

sounds like a bad ecm, you can go in to closed loop as low as 140F and the o2 is heated up to 500-600F to become active and swing. If you have headers you will need to install a heated o2 to obtain closed loop operation.

 

Maybe. All of the other components check out now so maybe the ECM crapped out.

What about the manifold air temperature sensor?

I have been using the stock o2 sensor when I put my headers on my car 10 years ago and have never had a problem. The sensor was really worn out (it was the original sensor with all the factory markings) so it was good if I replaced it.

 

do you have a scanner to see o2 cross counts. If not connect a vom to the o2 lead then the engine is warm. If the o2 reading is stuck at 0.45 volts the o2 is not hot enough or is defective. You can observe the mat on a scanner the ohm resistance is the same vs temp as the ect.If the mat is excessively high or low you will throw a malf.

 

I'll have to check that out. My friend has a scanner and I'll check that out with him.

Been pulling my hair out trying to figure out whats going on ha ha!

 

Just out of curioursity, you stated that your friend has a scanner. How did you know it wasn't going in closed loop without the scanner except for the TCC wasn't locking up ?

You stated that you are running an OLD O2 sensor.. Which from factory was a 1 wire. I would run a 3 wire sensor and it should fix your problem.

 

Field service mode of the ecm will let you know if your in open or closed loop.

 

The car was running rich, you could smell this in the exhaust. The car also wouldn't get up to 140 degrees. The car not getting up to operating temperature even after driving the car for 20 min on the freeway and the converter not locking up were signs of the car not going in to closed loop.

Also the car was still running rich after that same 20 min drive time on the freeway. The exhaust still smelled the same as it did when it was cold in open loop mode as compaired to the way it was running and operating in closed loop mode before.

We haven't used the scanner to check out the o2 sensor yet.

Yeah I'm still rinning the 1 wire sensor. What 3 wire sensor do you use?

 

acdelco AFS-74

 

Thanks. I'll check that out.

 

I originally ran a stock one wire O2 at the end of my long tubes and it only dropped out when the engine was idling
and the headers cooled off.
As soon as I drove off , it came back online again

 

I'll have to get one of these 3 wire o2 sensors. That may fix the problem too and its cheaper than getting another computer or going through another round of sensor changes that may not work.

 

A pigtail to connect the stock o2 is easy to build with packard connecters from mouser.com. You can hook the ground to a bell housing bolt the purple signal wires connect together and the accessory hot can be hooked to the cooling fan relay. Jims performance.com has the pigtail for I believe $20 amazon always has good pricing on the afs-74.