Stutter issue

[runamok]

Got a bit of a problem. Made a wide open throttle pass this morning and my floormat caused the pedal to stick briefly. Once the throttle reset the car had a noticable stutter during accelaration. Everytime it stuttered the air/fuel went lean. If I boosted it became almost unnoticable but part throttle cruising on the freeway or leaving a light causes a tremendous sputter or buck. I have to down shift to Drive on the freeway to lessen the effect.
Now the scan master shows nothing out of the ordinary. All parameters seem normal. No vacuume leaks. Pulling the plug wires one at a time showed nothing, each one caused the car to run rough and all were producing spark. All injectors are firing. I have a translator plus but unplugging the mass air caused the car to run rough, again nothing noticably wrong. It almost seems that something is cutting out but there are no trouble codes. Any ideas?

[Keller]

Give us some data on your combo.

Could be a lot of things. You say there are no vacuum leaks, but often a WOT pass can open a loose hose or clamp on the intercooler or intake path. Pulling a plug wire actually kills two cylinders, so it is hard to tell much by yanking them.

My suspicion is a loose IC hose, a fueling issue, something loose in the exhaust path feeding the turbo, or...maybe a leaking head gasket. Honestly, a lot more data is needed for a good diagnosis.

[runamok]

I looked over all the IC hoses and found all the clamps looked and felt tight. I have not checked the fuel side, my test gauge broke but I am getting another soon. I am running Cometic head gaskets and doing a quick water test on the headers revealed all cylinders firing. Vacuume is good on the gauge, it does jump when the car stutters, however that may be because the engine is stumbling and nearly shutting off. Is there any sensors that are not checked by the computer that might cause a stutter with engine load? The problem is hardly noticable without a load, I can rev the engine and it will be pretty clean throughout the rpm range, but if I put it into gear or drive it the problem becomes immediately notible. On a side note when the car is cold the problem is not there, when it starts to warm up it begins gradually then escalates to full blown. I don't know what to look at besides the obvious stuff. Any further info I can provide just let me know. Thanks all.

[kenmosher]

From your description, I'd be looking at fueling ... the change when it gets warm is suspicious. My thought is that cold enrichment might be covering up an issue with a sticking injector, low fuel pressure, dirty fuel filter or something?

It wouldn't hurt to pull the plugs and see if they read really lean (and replace them)...

[runamok]

Pulled all the plugs (NGK iridiums). While they looked a bit lean and showed some detonation nothing jumped out as a bad cylinder. I also changed out all the injectors (green tops) 2 by 2 but the problem still persists. I still have to check fuel pressure while running. It's the stutter when it gets warm that is strange. Can't put my finger on it. Since this is my daily driver I am overly frustrated at a hard to find problem. Aside from fuel pressure is there anything else to look at?

[Keller]

The fact that it won't idle clean with the MAF unplugged worries me. Did you unplug the MAF itself, or the Translator?

I am not a fan of the "gimmick" plugs such as those you have. Standard ACs or Autolies often have less issues, but they are likely not a cause as they are new.

What is the age of the coil and module? Have anyone you can borrow a setup from to swap on and compare?

[runamok]

Unplugged the MAF. I have an older translator but took it off because the translator plus had newer software and the car ran better with it. The coil pack is relatively new, year or year and a half or so, and the module is maybe three years or slightly newer. I will throw on the old translator and see if the problem persists. Think the module or coil might be causing the problem?

[Keller]

Unplug the Translator instead of just the MAF. That will let the ECM get the MAF error code and go into speed density mode. If it runs fine (unlikely) then you know the issue is MAF or Translator related. Chances are the issue is elsewhere.

I've used the Casper's tester to check many of my ignition issues, and the issues of others. Age is not always a good indicator. Non-GM/AC-Delco units are often not as stable or long lasting as GM/AC parts. Regardless, the easy way to see if it is working right is to swap with known good or new pieces. However, it is expensive to have these $$$ parts on the shelf. So having a TR friend nearby who will let you borrow his coil/module for an hour or so to confirm that is the issue can be very helpful.