Stumbles, Pops and backfires if she isnt warmed up for 1 min after start --- FIXED!
 

Hey guys, this is a 94 auto coupe with 125k miles.

After starting the car, if i dont let her warm up for a minute, she stumbles on acceleration, even light accel at 1500 or 2000 rpm. she barely moves and i can make about 15mph.

When the car is stationary and i rev her up, the revving is good, but as the rpm revs down it sounds like the engine is backfiring thru the exhaust, and i can hear many pops from under the hood. Does that sound like she's running rich?

But when the MAF is unplugged and i start her up, she runs great without any pops or stumble. I've replaced the MAF with no change at all.

This MAF thing is confusing, because with it unplugged, the car seems a lot more responsive at low rpm, and seems to have a little more power.

No codes, no SES light.

What else happens with i unplug the MAF? does it affect the closed or open loop? im thinking it might not be a MAF problem since a new MAF didnt solve the stumble or pops.

Is it true that most cars are designed to start rich? Is that programmed in the ECM? might mine be overly rich? or are some other sensors making her rich?



FIXED!

it was the MAF!

my bad, the first time i put the new MAF in, i didnt actually test drive the car and i called it bad. thats because i revved the engine in the parking lot and it "burped" many times from the exhaust like she was backfiring. i thought that meant that the stumble would still be there... so i didnt take her out for a drive.

a week later i sprayed electrical cleaner all over the MAF, and voila! no more stumble! woohoo! thanks guys for all your help!

Also don't forget that the MAF wiring and connectors might not be doing their job of moving current to the right place if they're damaged or shaking loose occasionally. Or the MAF logic on the PCM might not be being carried out, god forbid. It would be nice if you could get a live feed through something like auterra of what the MAF is reading when the problem happens.

:bigears

I have the same problem...

I have the same problem and I am suspecting maybe my MAF is bad.

Do you have someone who can swap their MAF temporarily with you?

The answer to this question occurs twice in the original post.

same thing here! yesterday mine started missing throughout the rpm range though. Today driving back from work the check engine light came on, was dying on me. 4 blocks from home at a stop light she died and would not start. had her towed home. Last week I scheduled an appointment to drop her off tomorrow on my way to work. It wont happen now! It acted like a bad TPS. Just my luck I cant find one anywhere local!:willy:

I had two MAF's go out on me. One was while driving back from town. Driving along fine and then seemed to become very sluggish, hesitation was bad and if I let of the gas the Vette would die. Took for ever to start back up, got her back on the road and started acting up again. Finally made it home and changed the MAF. Luckily I had one sitting around.

The other time I went to the bank and the car died in the parking lot and no matter what I did she wouldn't start up. Had a friend bring over a spare MAF and put it in. She stared right up.

How is your Opti... sounds like a timing problem except for the unplugging of the MAF and the Vette runs better.

Not sure but when the MAF is unplugged doesn't the computer go into a speed density setup. Seems I heard someone talking about that before. I might be full of it but wouldn't hurt to check your vacuum hoses and intake. If the computer does go into a speed desity setup then that could acount for the better response if you do have a vacuum leak because the computer would try and compensate for the extra air. Someone please correct me if I am wrong but I guess I am thinking out loud here.

Dave

Similiar symptoms but turned out to be my Opti
 

I had the exact same symptoms as described here, but my situation turned out to be the optispark.

I'm come to the conclusion that Corvettes are a collection of "single point failures" throughout the car.

What does the coolant sensor read when the car runs bad?

Well I only see it once and he doesn't specify where the other one came from.

So let me rephrase, because heaven forbid we repeat a question here on the forum, can you swap with a known GOOD MAF?

In other words are you sure the new MAF is good? If not you could use one from someone's car who is running right.

Like I said my car was doing this and yesterday finally gave up and would not start. The check engine light came on a few miles before. This morning I loaded her up on the trailer behind the suburban and hauled her the few miles to the dealership. They pulled the codes for free and it was the MAF. I bought the parts right there at a huge discount, changed it and she fired right up!! So home I went to take her off the trailer. I was so happy that I left a celebrational burn out!

Fixed!
 

it was the MAF!

my bad, the first time i put the new MAF in, i didnt actually test drive the car and i called it bad. thats because i revved the engine in the parking lot and it "burped" many times from the exhaust like she was backfiring. i thought that meant that the stumble would still be there... so i didnt take her out for a drive and returned the brand new MAF to the dealer.

a week later i sprayed electrical cleaner all over the old MAF, and voila! no more stumble! woohoo! thanks guys for all your help!

Great!

Now I need to do the same thing. :cheers:

what air filters do you guys use? K & N? im trying to figure out if the car likes a free-flowing filter like the K&N, or if that would cause lean backfiring.

Over oiling the K & N filter on MAF cars has been a problem for some, I don't know the exact symptoms but suggest searching the archives, good luck.

Yep, actually I think that is what killed mine.

I was thinking that, too. Although, I had a longtime member on here tell me he had never heard of a single instance where over-oiling lead to problems...I told him it happened to me, and he dismissed it, anyway. Another case of a dirty/oily MAF causing a problem in our cars.

to the OP...have you changed the air filter since the problem occurred? If not, you should.

Holy Resurrection, Batman. It has been 10 years so he either has solved it or moved on and looking at the correction, solved it seems to be the case. :D