I've done just about everything I can think of to trouble shoot the dreaded stumbling during acceleration problems and I'm not sure where to look next. I've read all the posts here on 20V and still haven't found a solution.

Here some details:
when cold, the engine stumbles and hesitates quite bad in the 2400-5000 rpm range. Once it warms up it's better, but still hesitates around 3000 rpm.

At light throttle it runs good, and wide open throttle it runs good. Just not in between.

Idle is rock solid around 1060.
Timing is set to 10deg
No Check engine light/codes
TSP is within spec for resistances. I also checked the resistance during a sweeping acceleration and it's a smooth increase, the value doesn't jump like I was hoping to see.
MAP sensor is receiving correct voltage from the ECU
ECU capacitors all look to be in very good shape
New Silicone vac lines.
New O2 sensor with correct 4wire plug from factory (not butt spliced)
Fresh premium fuel
New spark plugs
Spark plug wires are all in good shape.

I think the engine is running rich, i.e. backfires, bad fuel mileage, exhaust smells rich.

What else can I check?

Cheers... jondee86

Give a person a fish, they eat for a day. Suggest they search before posting, and they learn a skill for a lifetime.

Out of curiosity, how is that related?

Blacktop ECU also has some learning functions, and it can take a couple of days of
driving around after an ECU reset, to settle to correct operation. I believe the same
applies after changing the O2 sensor.

I don't have a factory spec for setting the timing on a BT. But I assume the 10 deg
(sometimes I read 8 deg ?) is base timing set with a jumper in the diagnostic plug.
And that the actual timing read after the jumper is removed will be more... say
around 16-17 BTDC ?

Cheers... jondee86

Give a person a fish, they eat for a day. Suggest they search before posting, and they learn a skill for a lifetime.

I did this and my timing is currently rock solid at 10deg. Unjumpered the timing went up to around 13~14 IIRC.

Maybe it will improve if you keep driving... good luck

Cheers... jondee86

Give a person a fish, they eat for a day. Suggest they search before posting, and they learn a skill for a lifetime.

I still need to double check the resistance of the new O2. Just to completely rule that out.

I would really look into physical stuff now. Like...is the fpr getting good vaccum? vacuum lines in order? fpr not stuck? fuel pressure in spec? is there a exhaust leak by the o2?

If the FPR was going out, wouldn't it be worse at WOT when more fuel is required?

I haven't checked the fuel pressure. I'll look into that too. Still using original 16v fuel pump. Also have a brand new fuel filter installed.

I did check for an exhaust leak near the O2 sensor. All bolts are snug and torq'd to spec, new gaskets on everything. It's all solid all the way back.

Brand new timing belt tension-er.

New midpipe

New O2 sensor

worth a shot

What's the easiest way to see what the pressure is after the regulator...?

While your doing that monitor the o2 sensor voltage after its heated up and monitor if it goes lean if you pull a vacuum on the fpr

if everything looks normal, then check the fuel pressure...

if it doesn't look normal, time to inspect fuel system more

The engine hesitates while under load. It idle's great, and the throttle response while sitting is good. I can rev with no problem. So I'm not sure if I could see a difference in running while the engine isn't under load.

If the FPR is closed all the time the fuel pressure going into the fuel rail would be high I would think. Could I throw in a gauge on the supply side to see if the FPR is plugged?

Correct me if I'm wrong, but this should tell me if my FPR is stuck if I have high pressure during idle and doesn't change much at WOT?

I still haven't figured it out.

My car was totaled last week. Some guy did an illegal U-turn infront of me when I had a green light.

SOO, I'm back to square one on the car, trying to see if I can salvage the car..

Your topic got my attention as I had this problem too when I first finished my swap. I didn't get a chance to completely solve it yet due to some engine issues (thus the car on the sideline right now), but did decipher it down to the fuel system.

I'm confident that once you get the fuel pressure gauge on there, you'll be able to see the problem. I'm actually looking to solve my issue once the car is back up with an adjustable unit one myself. I too installed a fuel gauge in there to be sure. My problem really frustrated me as I had motor done (such as cams and extensive head work), so at times the car would pull real hard, then others it would be gutless. After looking into what was causing it, I noticed some inconsistency in the fuel delivery. This added to my conclusion of the fuel system so hope when you get your car back in, you too will have luck with this. I myself plan to get a harden fuel line too as I don't believe the rubber hoses are cutting it.

Good luck man, keep us updated.

I bought my car back from the Ins Co.

Having body work to do, I haven't been doing much on the fuel problems. But as you mentioned Tekniq, I am leaning toward the actual fuel system. Hopefully in the next month or so I'll have time to get back into figure this out.

I was able to find another hood, bumper and headlight assembly at a wrecker. They had a sale going on at the time, $50 bucks for all you can carry. Turns out I can carry quite a bit when money is on the line, hah!

I didn't have the STA wired in.

all your sensors are fine, Toyota ECU require all there sensors for it to work. The ECU needs a wake up signal when the engine is turning over. You need to track down the STA wire and make sure its connected. I thought i had mine wired in but its wasn't. It needs to be connected it to the starter side of your ignition switch. Find the wire and back probe with an Ohm meter from the ECU (dissconect the harness from the ECU).

that fixed mine and it ran fine.

Im having a new problem. It revs fine put when i start moving it cuts out again. I know what the whats wrong now, I gutted the car to turn it into a Track Car and just now found the problem. The ECU need the Speed Sensor from the Cluster to drive. I through away all my old parts before i figured it out.

Hope that helps.