my Corvette has a nasty part throttle stumble when I accelerate. Very light acceleration doesn't cause it, and WOT acceleration doesn't cause it. It's when I'm somewhere in between that it'll sometimes happen. I temporarily blocked off the EGR a while back with no sucess, and recently I changed the oxygen sensor with no sucess. My next thought is that perhaps the MAP sensor is getting confused. So far I can't seem to find anything that's out of the ordinary with my auto x-ray, though I was focusing primarily on the oxygen and timing numbers until now. I'm getting no SES codes.

Has anybody experienced a similar situation?

 

TPS have a smooth swing?

 

I had a similar problem on another vehicle.

I changed the TPS and the problem was still there. I went to my mechanic and he told me the TPS I bought was not working correctly and he replaced it with another one and the problem was fixed.

I'd also, check to make sure the throttle blades open and close smoothly and aren't sticking at a certain point.

 

Oops. Yeah, I forgot to mention it but I swapped the TPS with the one on my IROC for a while and the problem persisted. I've also swapped throttle bodies with no help.

 

You mentioned you may think it's the MAP...most likely you'd have to datalog it for a tip in problem, scanner probably won't update quick enough.

 

It's not a tip-in situation. It's during acceleration when the pedal is held constant.

 

Regardless, your AutoXray may not update quick enough...FWIW, my SnapOn MT2500 isn't fast enough either to catch things, so datalogging is the best way to see blips and bumps in outputs.

Reminds me, I gotta go Ebaying for updated modules for my scanner...later

 

Does it stumble when the motor is cold and has been sitting overnight? Does it go away when the motor is warmed up? Reason I ask is because my Tahoe had the same exact problem and it turns out the cap and rotor was bad. I believe moisture would accumulate under the cap and would misfire under steady acceleration on first start of the day. When I pulled off the cap it was evident there was a lot of corrosion on the terminals.

 

Nope, just the opposite. It doesn't seem to do it when the motor's cold, only when it's warmed up. Everything seems to indicate that it's ONLY doing it in closed loop operation, which is why I keep going back to sensors.

I put a new MAP on last night. Right after the swap it still did it (though it seemed less severe), but on the way to work today it behaved.

When I get time I'm going to get the x-ray back on it and pay more attention to the knock counts and how much timing it's pulling out to see if it's doing more of that when I'm getting stumbles.

After that, I guess I'll put a fuel pressure gauge and a vacuum gauge on and see what I get.

 

i had the same problem on a stock v6 92 bird. it ended up being the wire from the coil to the distributor module. WOT fine, idle fine, but for some reason when i would lightly accel it would stuble and run like crap. maybe swap that out from the camaro and see??? I tried no egr, wires, plugs, new module, swapped in a known good distributor, checked grounds, fuel pressure. soon as i swapped in a new connection wire, ran great. what a pita

 

Unfortunately, that's not the problem here. I've got the large distributer with the coil in the cap. All of that hardware was recently changed.