For the last 2-3 years I have had a strange stumble/flutter I can never figure out. I've replaced and cleaned so many things on the car.
This happens only when cuirising on the highway at and is most noticable between 40-55 mph. When accellerating lightly the car seems to flutter and there seems to be not enough power for it to accellerate more efficiently. If i push the pedal down to say 50% itll eventually catch and go on as if it never happend. Car behaves great at ALL other speeds and rpm. This occurs a little bit worse up hills btw.

Finally today I noticed a strange patter in my CSV logs after doing probably my 20'th run trying to troubleshoot this problem :/

http://tobyz28.ath.cx/files/help.zip

Theres an excel file within that zip. If anyone who knows a good deal about interpreting these logs I would really apprecate the help..

At row 882, Please look at the L and R integrators, this seems to be a trouble spot... I should also point out that this is the exact point in which i notice the "Flutter".

The Left and Right integrator readings read higher on the right and lower on the left for exactly two rows (was polling at 250 ms/row). After 2 rows it complely switches, Lower on the left, higher on the right, and does that for 2 more rows. Then this continues as i give it more throttle until it finally gets out of it.

Can anyone help me diagnose this? I've changed plugs and wires many times, motovaced the injectors, cleaned the injectors, replace the engine block (another story), MAF, MAP TPS, Coil, etc have all been replaced. Plugs were gapped correctly too.

The Opti has not been replaced.
Fuel pressure checks out OK at Idle, WOT and cruise.
The O2's were replaced 1 year ago with Bosches, but appear to work fine elsewhere in the log file.
Injectors have never been properly flow tested or replaced either.

Does anyone have any ideas what this strange integrator readings could mean? Its looks like a miss thats alternating between engine sides. If it were injectors I'd imagine that it would happen on one side... O2's would report wrong all over the place.

Whats going on! I'm hoping someone will have a good idea of what this means. Please have a look at the log file, i posted some cell comments on cell 895).

 

Can't explain your logs but I think your problem is tranny. You already cleaned or replaced everything else. Many 4 speeds have a problem selecting the proper cruising gear when you get near the shift speed. Try putting it in 3rd and try the exact same thing as when the problem normally occurs. When was the last time you had the tranny serviced, THE RIGHT WAY not that BS back flushing?

 

Actually not that long ago, Flushed and then the pan was dropped and cleaned up. I've also had the tranny rebuilt It existed before and after the rebuild too...

Assuming it is trans related though, what would I look at doing to fix it or isolate what is causing the problem? Also, how would the trans cause the readings to flip around like that?

I do have Tunercat, is there anything I can do to prevent this from happening?

 

Try driving in 3rd and see if you notice the problem. It will eliminate many questions.

 

No problems on D. only in OD...
This only happens around 1800-2500 rpm, so when in D, its already well above that rpm in 2nd and doesnt happen when it switches into 3rd. Hope this helps.

 

The point was to drive it at the conditions that cause the problem but be in another gear. For example put the selector in D and drive at exactly the same RPM's as when the problem occurs in [D]. If the problem still occurs, you should look at the EGR and see if it is sticking. If you still have it, I didn't notice you saying you deleted it.

Hell if you still have it you should pull it anyway and look at it. Clean it and the seat and test it by sucking on the hose to see if it moves freely. Replace the gasket with a new one and put er back in. Don't pull the end of the pintle off.

Dave

 

EGR has been replaced and also blocked off in the past as well. It's now back on since i need it to pass emissions. There is probably only 5000mi on this new one and the flutter thing happend regardless of the EGR being on or off. I guess i should have posted that in the "things ive done" section

When I did put it on it held vaccume just fine when i sucked on it, and the car would stall out when I depressed it manually. (The old one had a "tiny" vac leak which probably didnt cause any problems at all).

I've also removed and cleaned the TB passages as well and cleaned the IAC pintle. I have yet to replaced the IAC since it appears (best as i can tell) to be behaving just fine.

Any more ideas on what it could be?
Does anyone have any idea why the CSV logs are showing the strange pattern?
Could this be my OPTI? From my years of searching it doesnt seem like the typical opti symptoms but it might explain why the car appears to be "missing" on alternating sides of the engine...

Thanks for the effort so far slopokrodriquez! If your frustrated with this problem yet, imagine how I feel! I'll try and drive at the same RPM in D later on today, I know if the hesitation does happen in D it'll be very very little, but i'm quite sure it doesnt do it at all.

 

i had that problem before when i first bought my car last july. I replaced about a grand in parts and finally i said screw it and went up to the chevy dealer, and was talking to one of the mechanics. I asked him to ride with me with the pcm checker and i got it to stumble and he said it was a piston not firing. turned out to be spark plugs actually ONE spark plug which in turn did give me a struggle getting off, the number 2 pistons plug and i cut my right eyebrow so i got a lil scar to remember it bye lol but i believe your problem is about the same, its definately something to do with the plugs, maybe your coil and opti

 

oh, i agree with the idea of drivign in d, when mine started happening all i did was pull it down to d and it was gone, mine seemed to be in a certain rpm range at afounr 50 ish also if this helps any, dont be discouraged though, like i said change plugs and maybe opti, and buy a gm coil because the msd actually make the optispark go bad faster