Code 172 and intake backfire

[1993BlackSHO]

OK here is the deal. My new engine is in and sounds like it is running well. Idle is smooth and does not sound like there are any misfires or anything. Here are the symptoms.

I noticed only when the engine is cold and I roll the throttle hard, it backfires out of the intake once. Once the engine is hot, no backfire.

KOEO - none
KOER - 172- O2 lean rear.

Anyone think these are related? I am ordering a new O2 sensor but Ive never heard of a O2 sensor causing a backfire. Im worried the timing belt jumped a gear. Just installed it while the engine was out. If the timing belt jumped would it cause the 172?

 

[1993BlackSHO]

Anyone?

 

[1993BlackSHO]

No thoughts on this. I did search and found nothng related.

 

[gas it]

How old are the plug wires and which brand are they? Is your car an MTX? If so it could be you have a bad baro sensor. It's on the firewall in the middle, looks like a MAP sensor but with no vacuum hose going to it. Unplug it and see if it runs better.

 

[1993BlackSHO]

Thanks, I will give that a try tonight. The plug wires are Motorcraft and not very old.