My car is a 1992 Buick Roadmaster Wagon, 5.7 TBI. with 185,000 miles. When I got it 4 months ago, it ran really well, just the slightest hesitation off-idle.
It was to be my winter beater here in Alberta, so I went over it all to be sure it would be reliable at 30* below zero. I changed the oil, changed the trans fluid and filter, changed the gear oil in the posi diff, flushed the rad, changed the rad and heater hoses and thermostat, replaced the fuel filter and air filter, PCV valve, plugs, wires, cap and rotor.
It ran really well, even when it was super cold out.
Then, it would run well when the engine was cold, but when the engine warmed up fully to 200*, it would start to act up, hesitate, miss, buck a little.
After sitting overnight at 20* below it would fire up fine, and run fine until the engine warmed up again.
In past experience that meant that the ignition module was failing so I bought a new GM module. When I was installing the module, I noticed that the wires from the pickup to the module were brittle and cracked, and that everything was pretty rusty. After twisting the wires to get them hooked up to the module, I didn't even expect it to start they were so bad, but it did. I thought it pointless to replace the pickup un a rusty, high miles distributor so I bought a new one.
Not wanting to use the Chinese module the new dist came with, I used my new GM unit. I set the timing to 2* advanced with the ESC disconnected, with it hooked back up, it jumped to 22* advanced.
The car ran better, but now, when you depress the throttle from a steady cruise state, it misses and bucks. It starts instantly, never stalls, will run from a dead stop to 100 MPH with it absolutely floored with no issues.
It coasts fine, if you take your foot out of it when it starts to shudder it's fine, just at any slight increase in throttle it stumbles. If you floor it when it starts to stumble it will rattle and buck like detonation, even on 94 octane.
So, to try to remedy this, to date I have:
Rebuilt the throttle body, no play in throttle shafts, 13 PSI fuel pressure.
Cleaned EGR valve, new gasket, no difference.
Replaced EGR valve with shiny, GM, auto wrecker one.
Replaced EGR solenoid with 2 different auto wrecker ones.
Replaced ESC module with 3 different auto wrecker ones.
Replaced Throttle Position Sensor with 3 different auto wrecker ones.
Replaced MAP sensor with 2 different auto wrecker ones.
Checked and replaced all the vacuum lines. Checked manifold bolts, sprayed ether (!) and carb cleaner around manifold.
Checked and cleaned all the grounds, new 900 CCA battery.
Multiple bottles of Seafoam through gas tank.


NO stored codes, have disconnected battery overnight to try to get things to reset, part throttle miss / bucking happens whether the engine is stone cold or fully warmed up.


WHAT COULD IT BE?
If I had any hair left I'd pull it out!
Thanks for any input or ideas.

 

I have a feeling it's the CTS sensor (front of the intake near the thermostat housing). Replace with an AC Delco part, I have not had good luck with the other aftermarket suppliers. I would buy a ALDL cable and download a free datalogger aswell, I would suspect you would have narrowed down the problem a lot sooner and spent less money doing so. I also recommend getting injectors professionally cleaned. This solved my poor idle and allowed me to pass aircare (in BC) before I sold my Caprice. All of which I discovered in one datalogging session after 5+ years of owning the car! Check the throttle body shaft for wear/vacuum leak aswell very common on these older TBIs now.

One last recommendation: Having lived in Saskatchewan I found a huge benefit in upgrading from a 1-wire to a heated 3-wire O2 sensor. This will get you into closed loop a lot quicker which allows the ECM to control fuel trims. I even found living in Vancouver that with a non-heated O2 in the fall/winter evenings the ECU would constantly switch from closed to open loop even with the car warmed up. Again, something I discovered once I started datalogging. Let me know if you have any more questions very familiar with these TBI B-bodies!

 

I am going to suggest it might not be an engine issue at all. Check your TV cable for proper adjustment. Next move on to the TCC lockup. It sounds like the torque converter might be trying to lock too soon. TCC Solenoid failure is pretty common on the 700r4 and in some modes of failure can cause the converter to lockup right after the 1-2 shift. The additional load causes the engine to run rough.

 

Thanks Fast!
That makes sense, the shifting is not quite as smooth as it was, but I attributed it to an iffy vacuum signal due to the rough running.
The trans is actually a 4L60 (not "E" though), basically a 700R4.


I've seen many of your helpful posts on the truck boards.
Vans Rock!
I have a 1991 G30 Cube Van, 350 TBI, 4L80E, DANA 70 w/4.88s, Ceramicoated Hooker longtube headers (36" primaries), Hooker H-Pipe, 47mm bored TB w/ultimate mods, bored and ported GMPP Vortec TBI intake, GMPP Vortec heads, Lunati Voodoo cam, MSD distributor, 6A box, wires and coil, and Hypertech Powercharger.
At a red light no one will get behind me because they think this big truck will slow them down. The body is all aluminum.
When the light turns green, she launches pretty good with the 4.88s.
I once stacked 40 cement 24X30 sidewalk blocks just inside the rear door, well behind the rear axle so I could unload them easier. When I punched it, it pulled the front wheels an inch or two off the ground.

 

That cube van sounds like it moves out nice. When I had my old G20 with a similar setup I switched the TBI for TPI. Love the way it accelerated though the midrange and pulled hills. I only had the 700r4 and 3.08s in the rear.

I have a 97 Express that has a moded up L31 in it too. Etec 170 heads, 215/220 @ .050 Comp Cam, LS7 lifters, Marine L31 intake, Doug Thorley Tri-ys, custom exhaust with a dual in/single out walker school bus muffler, swapped the 4L60E out for a 4L80E and soon plan to throw some 4.56s in the rear. I have A 9.5" 14-bolt with 3.73s in the van and only a 29" tall tire, but the swap to the 4L80E netted me a taller overall 1st and 2nd gear ratio and the desire for more punch off the line.

 

UPDATE: FIXED THANKS TO Fast355

Finally got a chance to drop my transmission pan and replace the TCC Lockup Solenoid.
It runs perfect again!
No more miss, shudder, ping or falling on it's face. Perfect seamless shifts and my good gas mileage is back.
What a relief.
If Fast355 hadn't suggested it, the transmission would never have been a suspect. I still can't believe how much of an effect torque converter lockup can have on driveability.
Message boards like this one are invaluable, someone, somewhere has experienced your problem and is willing to offer up their help.
This is the premiere TBI site on the web and I have learned a lot.
Thank you all.