Good evening all,
I'm popaX, returning to the forum after a lengthy hiatus due to Covid, and the demise of my '01 SS. As things would have it I recently became the proud owner of a '03 SS that had been garaged since 2021. Besides a dead battery(14), dry rotting tires, and a desperately needed oil change it started right up. I let it sit and idle after starting it up...it ran for a about 5 min...acted like it had a misfire...recovered then shut off. It restarts without any issues...runs for a few minutes...does the misfire thing...recovers...shuts off. Now, I drove it the seven miles to my home...it did the misfire thing while sitting at a stop light...accelerated without a noticeable issue...brakes working just fine. The service engine light came on about a block from my house. I parked it in my driveway, and let it idle while making a note of the changes in sound as well as the gages. Here's where I'm at:
1. It had 3/4 of a tank of gas
2. It had 173,000 miles
3. It warmed up from idling and driving yet never went over the 200 mark
4. The oil pressure went up while driving, but settled back down when parked and idling--the oil change filter should take care of that, and it had the proper amount of oil in the engine when I checked it before starting it.
So...oil change, new plugs, a half a tank of fresh premium or mid grade, fluid flush, and a diagnostic check to find the code then repair---that should take care of the misfire I hope, or am I still over looking something? Any help would be appreciated.

Thanks. PopaX
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2003 Monte Carlo SS, 2001 300M, 2010 F150 Supercrew, 1987 Turbo Thunderbird, 2009 Can Am Spyder RS

 

Sounds exactly how mine behaves when an o2 is going bad.

Welcome.

 

Hello and thanks wht02monte,
It's been a while and I had forgot all about the O2 sensors...they can be a bear sometimes. I guess I'll go out to rockauto and get some ordered in. With the amount of miles and age I can't go wrong with replacing them all.
Again thanks.

 

A bit of advice.. Find an ACdelco sensor. Cardone, walker, all the generics, Ive had problems with. Brand new sensors bad out of the box, almost everytime.

 

Hey wht02monte thanks for the confirmation, I have put generic-y sensors on my 98 monte z34 and on my 99 olds 88 and both did not care for them. Not sure if its a GM thing or luck, but I have found putting original manufacturer parts fixes the issue the first time 99.9 percent of the time. I did get a bad o2 sensor that was brand, but it was replaced without a hassle...

 

You could also be looking at a fuel issue. Car runs open loop at start, starts to warm up and then it switches to closed loop and starts to use the MAF + fueling tables. You can unplug the MAF and see if that helps too. May need a cleaning to the MAF, or something else is going on with the fuel system.

 

Given length of time sitting, my first impulse was what Chibi said, old/bad gas. I am guessing this Monte needs some maintenance/TLC.
- Before doing anything, get a fresh oil change!
- New air filter
- Check the engine codes (as those may give direct guidance on the issues)
- Fresh gas (clearly it can run on that old junk but it may be pretty weak). You could drain the tank (you could actually connect a fuel pressure testing host to the fuel rail, jumper the fuel pump with 12v at the fuse block and pump the gas right out) OR try and fill it up with good gas (to try and dilute the bad with the good).
- I am assuming the Monte is over 100k miles and may need some basic maintenance like:
---- New spark plugs and wires
---- New fuel filter
---- May want to change the trans fluid and filter
---- Before changing the MAF, I would try a MAF cleaner spray first.