Fox T-Bird/Cougar Forums  

My worthless two cents..
First check to see that all basic settings are correct, and no vacuum leaks, etc. That said, I have experienced your same exact symptoms, and the fix was: ICV (idle control valve), and 02 sensors are most likely your culprits.

Not sure I can record the pulsing....It actually feels like an extremely tiny miss. LOL. Hard to explain. You can't hear it, but I can feel it when driving own the road. very mild.

Better yet, disconnect both o2 sensors and see if things smooth out. Fuel economy will be worse on the highway, but the car will stay in open loop, and should run well under 14.7:1 at all times.

I doubt o2s are your issue though. The car will try to get them to stoich, but since it's not smart enough to see the banks are switched, when one bank starts to go lean, it will try to richen it up. Since it will start richening the wrong side, the other o2 sensor will read rich, and the EEC will pull fuel from the other, incorrect, bank. You will get one bank rich, one lean, until the EEC gives up and switches to open loop, ignoring the o2 sensors until next ignition-switch cycle.

When the car does this, the engine will begin to run rough since both banks will have bad mixtures. After a couple minutes of this at idle, it will fail the o2s and switch to open loop.

I'll run the old girl to a shop,

Run the cylinder balance test on EEC.. It may pinpoint a trouble cylinder and direct you to a problem with a plug, wire, injector..etc

With everything I've seen with tuning these things and trying to make them run smoother, I'm sure your o2 sensors are fine. It may be going into closed loop, but the motor(s) you built simply don't run very well with 14.7:1 AFRs and everything else that goes on in the motor (for example, the PCV, EGR, IAC are all undersized once the motor starts to pump more air through (higher load), not to mention the hotspots that get worse as you swap parts and make more power.

Basically, once you get away from stock, especially with older parts and wiring harnesses, and go to stoich, these will run rougher than when they were new, and stock - even with matched spark plugs and injectors, there are differences in aging in the wires going to each injectors, the spark plug wires will ALWAYS arc no matter what you try, other than coil-on-plug, and the floating grounds in the vehicle will always be all over the place, making signals inconsistent. I spent years chasing stock driving characteristics, but once you start changing things, you need to tune, then live with how it runs. Even the cylinders all breathe different amounts, some run hotter than others, etc. Restarting the engine throws more fuel into the cylinders, helping any leaner cylinders get the fuel they are staving for when in closed loop. I'm sure if you were to add a wideband sensor to each primary tube on some custom long tube heaters, the problem would be obvious.

I've been through two rebuilt engine shortblocks, 3 sets of heads, different rocker arms, pushrods, lifters, 3 different intakes, 3 different sets and sizes of injectors, various different plugs, lots of sensors, lots of different tunes, different exhaust setups, a few sets of o2 sensors, different fan setups, different throttle bodies, iacs, maf sensors, and so on. The engine still behaved the same though them all, using the same HO cam from an '89 Mustang. A low mileage, well kept stock HO mustang runs smoother than my engine, and a SO motored vehicle runs even smoother than that. I've given up trying to make a heavily modified engine, designed decades ago by someone else, run the way I think it should.

Can you grab a camera (phone) recording of the pulsing. Could be many things, depending on how bad it is. It could be something that has always been there, but you're now feeling it due to aging motors mounts.

I've never had any of these issues with my Thunderbird. It's still running the factory A9P tune with a calibrated MAF for 24lb injectors. Cold, hot, cool, warm doesn't matter. Starts up after two revolutions and settles to a 700rpm idle in park. I pop it into drive and the idle does down to 650rpm. Drives around like a new car with no stuttering, popping, or any issue. Power comes on linearly and never falters. All the EEC grounds are good and any wire I added (MAF conversion) is soldered. I've never hooked a quarter horse or any tuner up to the car. I'm pretty sure if I did it would shatter the illusion I have of how well the car runs :hick:.