Hello All,

I purchased a 91 Firebird 6 cyl. with only 29k miles on it about 2 months and I'm having problems with the 'Service Engine' light coming on intermittently, the car idling too high just about all the time and poor gas mileage (about 10 mpg even on the highway). The symptoms are as follows;

1) the car never idles below about 1050 rpm's (even after it warms up) and when it's cold, the idle continuously fluctuates between 1100 and 2200 rpm's when it's in park or neutral. I've never owned a 6 cylinder before but I assume the idle should be around 750-800 rpm's when the cars isn't in gear.

2) the Service Engine Soon light comes on and stays on frequently whenever the car is standing still for more than a minute or two (i.e. at a red light) no matter what gear it is in (including neutral) and no matter if the engine is cold or warmed up.

3) all the gauges (except for the tach) indicate that the engine is running fine. i.e.. not running hot, plenty of oil pressure and voltage, etc...

4) the light goes out about 15 seconds after I start moving or if I rev the engine once while in neutral or park.

5) the mpg is only about 10 to 11, even if I'm on a highway.

6) I've scanned the car a few times and there are no codes, not even code '12' which I believe should be there all the time.

7) given the low mileage, I've assume that the car sat for extended periods of time so I've changed the oil and used up the old gas and refilled it 3 times including filling it with 93 octane the last fillup.

Any and all advice on how to fix this problem would be greatly appreciated.

thanks

 

How did you scan the ECM? If using the jumper to blink out the codes, you should get a code 12 twice (I believe) and then any other codes should blink out (twice again I believe) and then repeat as long as the jumper is connected. If no code 12, you have an ECM issue. Re-post in the ECM section if you suspect an ECM issue.

 

Thanks for your response... I scanned it with a handheld OBD1 scanner. I've scanned several other cars with it and I know the scanner works. However, I can try jumping the terminals if you think it will make a difference.

I've searched the forum for similair problems and only found ones with specific codes pointing to the problem. However, since I've got no codes to work with, I'm at a loss as to where to start so any suggestions would be helpful.

thanks again.....George

 

Have you checked for vacuum leaks? Vacuum leaks allow extra air into the engine which the O2 sensor sees as a lean condition and will try to compensate by adding more fuel. A bad O2 sensor will also cause erratic idle and poor gas mileage. HTH!

 

Hi....thanks again for your response.

The first thing I checked was the vacuum lines. They all look new and since they looked new, I checked to see if any of them were collapsing when the engine was running. Years back, I had a cheap relative who used windsheid wiper tubing instead of real vacuum tubing because it cost less. Drove me nuts trying to diagnose his car because the lines would only collapse when the engine was above idle causing the car to run like crap.

I'm going to replace the O2 sensor next since they're cheap and looks easy enough to get at. Unfortunely, I was injured in a bad accident years ago so I have to depend on my son to do all my repairs for me and is why there's sometimes several days between my responses.

thanks again.....George