Stumbling at idle ONLY after hot starts
 

Just put in BHR coils and plugs less than 500 miles ago. No issues starting the car hot or cold, no issues driving the car cold, no issues driving the car once warmed up from cold.

However, when I start the car hot (after letting it sit for maybe less than a half hour), it will start but will stumble from 1,000 to almost dead. At one point it stalled when doing this, but most of the time the ECU catches it and saves it.

If I hold down the gas and rev it up to 1500-2000 rpms for a few seconds and then let it idle, the issue goes away. I'm really confused.


Edit: During a drive today the stumbling happened so bad at one point that I would start it, it would immediately die. However, if I revved the engine before it died I could drive and the issue went away.

I've also noticed the engine artificially idling at 1,000 rpms sometimes when it normally idles at 850 rpm (factory map).

Sounds obvious, but did you also replace the ignition wires along with the coils and plugs? And are all the wires seated fully on all coils and plugs? I don't remember if you said you had done a rotary compression test on the engine yet ? Might also need to reset the ECU.

Yeah did coils, wires, and plugs. I have a gnawing feeling it's the engine going out on me, but I still need to get around to cleaning the MAF sensor and e-shaft sensor to see if that's the issue because what I've described happens on and off. I would think that if engine compression was really suffering that it would be affecting my performance a lot more than just occasionally at idle.

Yes clean the MAF and ESS sensors. Could also be an O2 sensor problem, and as I stated before, you may need to rest the ECU after cleaning. If none of that works to solve your idle problem, yes it could be a failing engine, but try my suggestions and those from RIWWP first,hopefully these will be a simply fix.

Quote from moderator RIWWP to another member having idle problems:
"this suggests that your fuel trims are currently running you too lean, so that initial gasp of air makes you go so lean that the engine has trouble staying alive.

Since you got a code of "system too rich", this does point at a sensor malfunction. Basically, if the ECU thinks you are too rich, it has probably kept pulling fuel like crazy trying to make you run leaner, and you are running leaner, the ECU just isn't aware of it, still seeing the rich signal.

If I was in your shoes, I'd buy a bluetooth OBD2 adapter, pair it with my smartphone, clear the fuel trims with a battery disconnect, and then fire up the car and let it idle, and watch my short and long term fuel trims to see what they start doing. Also watch my commanded vs actual AFRs, to see what clues I could get about which O2 sensor was the one that the ECU was reporting the 'too rich' off of.

If I couldn't figure it out easily that way, then I'd disconnect the rear O2, reset the fuel trims again, and then repeat. If the fuel trims and AFRs stayed fine, then the rear O2 is the one with the problem, if they still go out of wack, then it's the front O2 sensor. "

It's a 2005. Current mileage is about 96,000 and I'm fairly certain that's on the first engine. Most cars should have had a swap by now I'd think. The first owner bought it from a dealer in 2006, put about 50k on the car. Carfax doesn't obviously show any major car work other than standard x,000 mile maintenance. Second owner put about 42k on the car, and now I've put a few thousand on.

When the emissions people made me take the car into a mechanic for CEL "diagnostics" the mechanic that checked my car said the O2 sensors were fine. I had specifically said I thought the problem may have been with the sensors after doing some research myself but he seemed to think that there was no problem with them and that it was the catalyst, which I agree with because weak ignition coils will kill a cat pretty quickly.

I had a similar problem a while back. I solved it by cleaning my MAF and my ESS. I have got to say, my ESS was DIRTY!!!! After I did all that I had later found a problem in the wiring with my Low Fuel Pressure Resistor located under the air compressor near your washer pump. I fixed the wiring and cleaned my sensors and have yet to have a problem since.

Hope this helps.

Yep, just went to O'reilly's today and picked up some shop rags and MAF cleaner. I plan on wiping off the ESS with a rag and then spraying the MAF sensor with the MAF cleaner.

While waiting for my sister the other day at idle, I noticed that, without idle RPMs changing from about 850, the car would run very quietly, like you'd expect. Then, somewhat predictably but still kind of random, it would start to vibrate and shake the car a lot more.

We will see how it runs after I clean the MAF sensor and ESS, and I am hopeful.

I also picked up some 2-stroke oil. They didn't have a lot of options for non-TCW3 2-stroke so I had to go with a semi-synthetic JASO FC certified oil but I think that will help prolong the life of this probably pretty tired engine.

Edit: I just remembered also just ordered a BHR midpipe with cat yesterday and will probably have it installed next week so that should get rid of my P0420 code and clear my CEL for now. :D