[92Mustang5.0LX]

So I cant seem to figure this out. I replaced the negative battery cable. After that the car has had s***** idling when started. 500 to 1000 then to 500 then to 700. I had a thread for it and thought I fixed the problem but no. Someone said drive it so the computer re-learns. well that hasn't worked. After about a week (it stalled twice) I checked for codes. got 91. In my book it says o2 sensor running lean always. the car also got really hot today. reservoir coolant was bubbling. never done that before either. I went home replaced both sensors. (non aftermarket) I started it up and it seemed fine till I went to the store and came out to start it and it did the same thing went to 500 rpms then 1000 then to 700. I noticed when I pulled into the garage I was rolling the windows up and when I would use power( like the head lights or power windows) the rpms would go down a little. never noticed that before. I don't understand whats going on with my car. no other codes either.

 

[fordman777]

Alternator and battery check out good? If it's running lean you need to trace the cause down. Which bank did that specify for on the O2? Vacuum leaks/unmetered air can cause bad idle/stalling as well as lean conditions. Also exhaust leaks prior to upstream O2's can trick them into thinking there is a lean condition.

Also I know you have probably done it already but double check that ground and make sure it is clean.

 

[92Mustang5.0LX]

Battery and alternator are good. It didn't specify a bank. just gave me code 91. after I replaced both o2's yesterday ive driven it about 40 miles. now I have code 41 and 91. I think I need to drive it more though. Whats unmetered air? I do have the smog pump deleted and the 2 vacuum lines that were connected to the smog pump are clogged shut with some kind of cement stuff I got at a auto parts store. that was 2 years ago. could that be a cause? its so weird after installing this negative battery cable now my idle is ****** up. it got really hot the other day driving too. coolant was bubbling in the reservoir. never seen that before either.

 

[fordman777]

41 O2 sensor signal/lean fuel mixture.

91 Oxygen sensor problem, fuel pressure out of specified range or injectors out of balance

If the O2's are good you need to verify the wires and harness is good. Also check fuel pressure and injectors.

Clearly you are getting a lean condition. Either you are not getting the amount of fuel desired by the ecu to keep the AFR stoich...or you are getting unmetered air. Unmetered air is air entering the engine unmetered by the MAF. Vacuum leaks are the most common. Exhaust leaks prior to the upstream O2's can cause problems as well...especially at idle.

I would start by checking fuel pressure and for vacuum leaks.

 

[APOCALYPSEof87]

+1 for Fordman777

41 O2 sensor signal/lean fuel mixture.

91 Oxygen sensor problem, fuel pressure out of specified range or injectors out of balance

If the O2's are good you need to verify the wires and harness is good. Also check fuel pressure and injectors.

Clearly you are getting a lean condition. Either you are not getting the amount of fuel desired by the ecu to keep the AFR stoich...or you are getting unmetered air. Unmetered air is air entering the engine unmetered by the MAF. Vacuum leaks are the most common. Exhaust leaks prior to the upstream O2's can cause problems as well...especially at idle.

I would start by checking fuel pressure and for vacuum leaks.

Check fuel pressure, should be 36-41PSI.

If you have a propane torch turn it on but don't light it.

place the torch end near the vacuum hose(s) where you think the leak is, if the engine rev's up or smooths out, then that's where the leak is!

 

[ciesielski]

Is your coolant still boiling after driving it? If so, check your rad cap. If that is the reason you are running hot it could be the cause of some of your problems. Give us all the info possible and I think we can solve this problem. I think you have a mechanical problem and not a sensor/electrical problem.

 

[fordman777]

He never stated to be exact but sounds to me he has problems before the car gets warm. That would point to a lean condition which could however cause over heating problems. Detonation can destroy an engine just as fast as over heating.