Hey Guys,

I'm working on my buddy's '94 GT 5.0 and it has developed a strange idle. If you sit w/ it in drive for a minute the engine starts to lope a bit, but it's perfectly fine at all other engine speeds.

Shortly after it started doing this the check engine light started popping on occasionally & then going out. I ran the codes and got a 172 & a 176, which list as 172 (R,M) Oxygen sensor not switching - system is or was lean - Single, Right or Rear HO2S - Fuel control and 176 (M) Oxygen sensor not switching - system is or was lean Left or Front HO2S - Fuel control

So the computer is showing a lean condition left, right, front, and rear, apparently only occasionally because the light only comes on once in a while when driving.

Can anyone tell me what these codes mean & where I should look for a fix? My buddy needs the car in two days to drive home to see his family for the Holidays!!


Sorry to cross-post, but I'm short on time...

 

Lean condition ussually means a vacuum leak. Since it only happens when driving, then you probably have a vacuum line that has a crack in it that opens up when the line is wiggled/vibrated. Quickest way to figure this out would be a smoke test (running a special type of smoke through the vacuum lines and look for the smoke leaking out). While its a simple test, the smoker unit is expensive. So you'll have to take it in to a shop to do it. An alternate method would be a visual inspection of all the vacuum lines, looking for rot/deterioration/breaks, replacing any that look bad. Kind of like looking for a needle in a hay stack, but you could get lucky. Note: some lines have covers, or tape on them from the factory so make sure you remove the covering/tape etc while hunting and putting it all back on afterwards.