Sometimes car stalls when declutching, especially in reverse

In a nutshell, sometimes my car will stall or revs will drop to 200rpm before it catches itself and shoots up to 1500rpm and then bounces around in smaller increments until it reaches 800rpm where it purrs. But sometimes it doesn’t do this. Sometimes a cold start will have erratic idle or almost dies, and the car will have a lumpy idle like I have race cams in it (but I don’t). Other times a cold start is just peachy. Then on the road, car cold or warm, when I push the clutch in to coast to a light the revs will dip and sometimes stall. I can start the car right back up if it does stall. Once the erratic idle stabilizes at 800rpm, it will sit there and purr. Wet weather seems to make it worse. With the car just sitting, if I rev to 3000 rpm and take my foot off the gas, the revs will dip and either stall or bounce around in smaller and smaller increments until it gets back down to 800rpm. Here’s what I’ve done so far (that I can recount, there might be more…):

-Tons of engine to body grounds, including 3 grounding straps.

-Cleaned my positive battery cable connections.

-New O2 sensor with dedicated ground, grounded at the ecu grounding spot on intake manifold.

-Checked injectors, no leaking or apparent clogs.

-Cleaned throttle body.

-MAF is within spec.

-Cleaned idle air control valve

-Coated my engine bay with carb cleaner but didn’t find a vacuum leak.

-Ran the car without the idle air control valve plugged in but the behavior didn’t change.

-Adjusted idle screw up a bit.

I can also smell a bit of exhaust in the cabin with the HVAC system on, but this is more recent so I doubt the two are tied together. And since this started, I am getting worse fuel economy, I presume because the engine thinks I’m lean when I’m really not.

This seems overly obvious, considering the amount of work you have done, but what is the condition of your spark plugs and wires? Your statement about wet weather making it worse makes me think you have carbon tracking in your wires. If you haven’t done so recently, replace your plugs and wires with new. Go with OEM style parts, nothing gimmicky. Regular old Denso or NGK will work great on this car.

Thanks for your quick response and for bringing up other things I left off my list. I recently did a full tune-up of the car, where I replaced plugs, wires, cap, rotor, PCV, and probably some other things. I also swapped out my EGR for a used one from a friend and replaced the EGR-BPT valve with a new one. The problem was occurring prior to these changes and none of these things affected the issue.

Bad coil?

Have you tried to use a troubleshooting flow chart? you are using a diagnostic approach that has no clear stratagy to it, you are simply hoping to stumble on the cause of this concern. This is a costly approach to use. What year model is your car?

I think I may have found the answer, but it will take a few days to confirm. I swapped in a MAF from a friend with the same engine and so far it appears to have solved the problem. I will report back after the weekend as to how it is going. Thanks for all of your quick replies and I hope this solves it!