let me get right to the point.

im getting a lean exhaust code on a 87 z28 305 tpi. it mostly shows when at a stoplight or stopsign for a couple minutes. the car is always warm when it happens (between 150 and 170+) and the idle will drop to 5 or a little below, it will code, and then idle at a little above 5. for the past couple of days it has also come on when im at various speeds (35, 50, 70, 80) today it came on while at a light waiting to get on the highway and even at 80 it still stayed on.

i have a new o2 sensor, new tps (properly set at .54 and even bumped up to .57 and .59), new iac, new cts, new fuel pump, new fuel filter, checked and replaced vacuum lines

anything new i put on stops the code for a day and then it goes right back to it again. and yea i reset the computer each time i put a new part on. im totally clueless here and i could really use some help.

 

Check your fuel pressure.

 

it was within specs

 

Okay, here is some serious armchair mechanical troubleshooting.
1. Are you SURE that your car is truly going lean? If not take it to a shop with an exhaust sniffer and find out.
2. What about your voltage? Is it fluctuating? Don’t rely on the dash gauge, put it on a machine if you don’t have a clamp on voltmeter/amp meter.
3. Did you make any changes to the vehicle just prior to this problem starting including tune-up?
4. Does anything else happen when the idle drops? After it pops the code then the idle returns to normal. Does the idle continue to cycle indicating that this problem is continuous and not just one time after a throttle position change.
5. Have you checked all your grounding wires to make sure they are securely attached with no rust or paint? This includes the battery cables.
6. If all seems good to this point then you should start considering getting a new ECM. They don’t pop a code and say, hey, I’m not working right. Considering the amount of money you’ve already dropped the $125 for a new ECM would be worth it.

 

1. no i am not sure
2. new alt and battery shouldnt be a prob.
3. i had it before i put on chrome valve covers, since then it has gotten worse.
4. no it seems fine after it codes and is fine prior to the drop. once the drop occurs it almost dies and then codes and goes back to normal.
5. never touched them they should be fine
6. that sounds a little steep to put into something that im not sure it is. i dont want to put 125 in an ecm and then it be injectors or MAF i just dont have the money to drop on anymore parts until im almost positive its that part.


i took off the plenum and i heard a hissing sound coming from the front runners on the driver side. checked the plugs there and they were fine.

 

Disconnect the MAF and see if it still happens, the car will still run with the harness unhooked. If it does then the MAF isn't the problem. As for the injectors, they aren't all going to go lean at the same time unless the computer causes them to. Hook up a vacuum gage and see if you get any big changes when the engine almost dies. I'm leaning more toward the ECM after your last responses.

 

maybe you could help me out too....


my car puts out black smoke at idle and burns your eyes....
i've adjusted fuel pressure and checked timing.....
o2 voltages are low but no codes
only code it sets is egr after driving.i figure it sets that because it is disconnected.........
i just hate the black smoke and you can't even stand near the rear

 

could my map sensor be bad? the relays there have all gone bad and the MAP sensor is the onlything over there that hasnt been replaced. i think water dumpped onto those relays and i dunno maybe it got the map sensor too.

my car has always had this problem where it thisnks it is going to overheat. if i sit in a drive-thru or in traffic for a few mins it starts to really get up there. the guage moves rapidly but yet a guy that i use to have work on my car said it is no where near as hot as the gause says. could this cause the problem since it is always when in closed loop?