Hey all. I have a 2002 Impala LS 3.8L with 103k miles and it was running fine. I decided to get the 100k maintenance done and changed the plugs & wires. The plugs I used are AC Delco 41-101s (.060 gap i checked) which are the direct replacement for the stock plugs. I used Duralast plug wires from Autozone.

I installed the front 3 plugs (1, 3, 5) & wires first because that's all I had time for and the vehicle ran normal for 2 days. Then I installed the rear plugs (2, 4, 6) & wires and it seemed normal at first. I went to run an errand and once the vehicle was at operating temperature it would stall at lights and stop signs when idling (800~ rpm). It starts back up with a little coughing. I'm able to keep it from stalling with a little gas at 1000rpm. The RPMs do NOT flutter when I give it gas and hold it, only when idling under it's own control. When the motor is stone cold it will idle fine until it hits operating temperature then sputter and die (did this in my garage). If I revved the engine while in park it sounds normal up until 4000~ rpms then starts to sputter. I put all the old plugs and wires back in and it still stalls. There are no check engine codes and I triple checked everything to make sure of a tight fit.

I'm at a loss here! Car has ran great in the 45k miles and 3 years that I've owned it. I would think if it was an O2 sensor or idle air control sensor it would throw a code?? Any input is appreciated.

 

Drove it to work this morning. Took the freeway and set cruise control at 60mph which puts the rpms around 1800~. RPMs stayed constant, no surging. I'm getting a faint exhaust smell in the cabin though. Would an exhaust leak or bad catalytic converter cause the symptoms above without a code?[/align]

 

If it didn't act this way before you did the work, it sounds like something happened. Do you think you might have knocked something loose changing the rear plugs?

Can you put a scanner on it, look at live engine data? Just because something should set a code doesn't mean it will. Can you tell if the system is running rich or lean?

 

Yeah I figured since it ran fine before changing the rear plugs I MUST have knocked something loose....but I swear I looked over the engine 10 times and didn't see anything unusual. When I pulled the motor forward it only moves an inch or two, and it's supposed to do that without the front mounts in place. The only loose connector I saw was a blue one on the harness near the alternator on the top passenger side of the motor. I never disconnected this manually and it looked like an unused plug because it was dirty, unlike a sheathed connector. Usually if something is disconnected like that it would throw a code (I would think anyway). I looked all over and didn't see any open female plugs that it would go to.

Unfortunately I do not have a scanner. It did throw a temporary code at one time and I took it to Autozone and hooked up an OBDII reader. The code was P0300 I believe, random misfire. But that could have been the one time I forgot to hook up a plug wire when I was testing stuff (I installed and removed plugs/wires a bunch). It went away shortly after I hooked the wire back up. I might have to take it to a shop for full diagnostics...I just hate spending money on that stuff. Stubborn. [8D]

I think it MIGHT be running rich, only because there seems to be more exhaust and moisture coming out of the rear pipe than normal...that's a guess though.

(NOTE: After talking to a shop I found out that sputter at 4k~ rpms while in PARK is normal because the rev limiter is kicking in. I thought that might be it, but wasn't sure. So I basically just have the idle/stall issue and less power.)

 

After having a shop run diagnostics on it they told me it was a bad O2 sensor. Unfortunately I thought a bad O2 would throw a code but I guess it doesn't depending on how far gone it is. And having it go bad at the exact same time I changed my plugs was a horrible coincidence that made me think it was something I did. The only bright side to this debacle is I got so good at installing and removing my plugs I can do the whole job in 25~ minutes.