Hello folks,

I have a ’91 Firebird Convrt with a 305 ci V8 (LO3). It has 80k original miles on it. I have been having the Check Engine Light come on intermittently, mainly after it has been driving for a bit, and it runs very rough until it warms up. It never stalls, but the RPMs jump up and down and until it warms up there is major hesitation and loss of power when you accelerate. It actually idles pretty well if you let it sit there and warm up first.

I have been searching your boards (Very helpful!!) and used the paperclip procedure to get the codes. Here is what I found (I got the meanings from your site):

12. No reference pulses to Electronic Control Module (ECM).

23. Low temperature at manifold air temperature sensor OR
Throttle position sensor error

32. Fault in barometric pressure sensor circuit OR
Fault in exhaust gas recirculation valve diagnostic switch OR
Fault in electronic vacuum regulator valve

44. Oxygen sensor lean.

My question is how do I get the Check Engine Light to not come one?

Could this be the reason it is running so rough when cold?

Thanks…

 

91,

Welcome Abaord!

In no particular order:

Yes, the error codes are likely indicating a problem that is at least contributing to your cold/rough running problems;

Yes, the Tech Boards (like any other tool) can be very helpful (and a little bit of fun, too!);

The way to prevent the "Check Engine" light from turning on is to repair the problem(s) that the ECM is detecting;

Your error codes indicate a few notable things:

• The '12' is normal when the ignition is on but the engine is not running. Since that is the correct mode to retrieve error codes, you'll always get a '12' unless the ECM has a serious problem;
• The '23' indicates a problem with the MAT/IAT sensor. The code is for an impossibly low temperature indication from the sensor (less than -40°). Unless you store your car in a deep-freeze, it's likely that the sensor has failed or is not connected (open circuit);
• The '32' in your application is for an error in the EGR system. On a TBI engine, the EGR function is sensed by the MAP sensor. Diagnosis of the EGR valve can get rather involved, but you need to repair the other issues before proceeding. It's possible that repairing the other problems would solve the '32' as well.
• The '44' is for a lean condition, which could be a fuel mixture problem or oxygen sensor problem. If the oxygen sensor is more than 30,000 miles old, it's probably time to replace it as a matter of routine, preventive maintenance. Even if that doesn't solve the error code, you'll know that the signal from it is corect. O˛ sensors degrade slowly over time, and don't typically last for the life of the vehicle.
  
  Other possible mixture problems are low fuel pressure, vacuum leaks (including the EGR), and injector spray pattern problems.

Since a few of the error codes invlove engine sensors, it would also be good to verify that the electrical grounds on the engine are clean, tight, and intact. It only takes a couple of minutes, but can make all the difference in correct data to the ECM.

Keep us posted on your progress, please.

 

Thanks for the quick reply, Vader. That was very helpful.

Well...I changed the MAP sensor (wish everything in life was so easy ) and cleared the codes. The rough running at initial, cold start is still there. I am not sure that changing the MAP sensor alone has resolved the "Check Engine" light, as it was an intermittent problem and I have not driven the car enough since the repair.

About the O2 sensor, that does not seem as straightforward. On my F-Bird is that on the driver's side exhaust manifold, way down near the firewall?

-If so, what is the best way, tool to get to it? It's a tough one.

-Also, at the parts store they listed 2 different O2 sensors for my engine, one had a small male or female connector at the end of the wire and the other had a more complicated plastic connector. Would you know which one is for my particular engine? I realize that the best way to tell is to take the old one out first and take it with me to the parts store.

Thanks again for all your info and help...

 

O2 sensor is very easy. Get under the car and look at your Y pipe. You'll see a small cylinder with a wire sticking out. Look at the connector on it-that's the kind you'll need. Bosch makes a direct replacement for $20. Heat up the car for just a minute...just enough to make the exhaust piping warm, but not hot. That'll expand and loosen the metal a little bit. They make oxygen sensor sockets to remove them, but I find those pointless. Use a wrench and a rubber/lead mallet...it'll work just like an impact wrench and will have that sucker out of there in 30 seconds or less guaranteed or your money back. Screw the new one in carefully and reconnect it. Simple as can be. Just reset the ECM after you're done or the car will start to act all weird on you and throw codes that don't make sense.

 

If you're really determined, you can get it from the top:

 

Yeah, but......why?

 

Excellent pic, Vader. So far the CES light has not popped back on so I am hoping that the MAP sensor did the trick.

BTW--with my engine, which is 1991 5.0 TBFI V8, is there a fuel injector cleaning or service that could be done. I am wondering if that could be causing my "major hesitating and RPM drop" when it is cold. My other thought is a Tune up?

Thanks again folks...

 

Change your fuel filter

 

Thanks, RB83L69. But, I forgot to mention I have done that twice already in the last month. I also used a bottle of that "water separator" treatment in the tank. I originally thought my problem was getting some bad gas. I have already used up that tank and refilled.

 

If you haven't done so in the last 20,000 miles or so, a good tune up would be well worth your time and effort. Make sure you test fuel pressure as part of that.

 

How Do u Know what error codes you are getting?

 

https://www.thirdgen.org/newdesign/faq/thirdgen.shtml

Scroll down to Miscellaneous. First item. Super-easy once you know how.

 

NAPA sells a kit which you hook directly to the Schrader pressure valve (I know you have one, you have fuel injection, just may be harder to find on a TBI car than on a TPI car) to clean the injectors. I saw it on TV. It works great, so I've heard. You attach the hose to the valve on the pressure line and disconnect the fuel pump so the engine isn't getting gas, then you attach the other end of the hose to the can and start the engine. The engine uses the cleaner as a fuel, so it runs like it normally would. Use about half the can and then turn the engine off. That's all there is to it. I can't wait to do it over the winter.

 

you may need to reset your IAC motor or possibly replace it that was the cure for my car acting a fool