Guys I'm having problems tracking down a studder or hesitation, while slightly depressing the accelerator. If I accelerate hard it doesnt do it. It does it everytime if I'm coasting for a few seconds and then barely press the pedal it will surge like someone is holding a kill switch down and then it resume accelerating, this take place in just a couple of seconds. It started about 3 weeks ago when I changed the spark plugs, so I thought maybe i didnt get one of the plug wires back on good. So i checked the wires per the FSM all under 35K ohms, still didnt help so I bought factory wires, rotor, cap, still does it. I've checked for vacuum leaks with starter fluid, but didnt find anything. Pulled all the plugs none of them were wet looking all looked good. Fresh air filter, TPS was replaced with OEM toyota about 50,000 miles ago, the whole engine was rebuit about 50,000 miles ago so i checked everything per FSM before re assembling. This one has me stumped. If anyone has any ideas, bring them on.

Thanks

mine did what you described, didn't know what the problem was until I cleaned out my throttle body of black sludge, and found out that my timing was retarded. check your timing. stock is 5* jumpered.

timing is good, it was 5 jumpered and about 12 without jumper. I thought maybe I got some bad gass but its been several tanks since then. I'm wondering if maybe the O2 sensor is going out.

Thanks

Checked the TPS this morning, checked out perfect, reset checked timing, idle, all were fine. double checked for vacuum leaks, found none. This morning while driving seems I can make it happen for a long time if i keep the pedal just barley depressed, I hooked the tack up and it seems to start around 1200 RPM, this is with the the pedal just barely cracked open maybe about a 1/8" moving the butterfly. I was going to check the O2 sensor, but I only have a Digital Volt Meter and when I tried it just read 5v DC the whole time so maybe I need to find a analog so i can see the on and offs of the signal.

Your timing should also advance instantly as soon as the throttle opens.
If not you will bog, studder and hesitatate...

Your TPS controls this operation

Yeah it advanced perfectly and never jumped around. Everything is that would normally be related is fairly new except O2 sensor, Injectors were rebuilt when the engine was rebuilt. The exhaust smells like its not burning all the gas r something, its a weird smell, there is also alot of black suit on the edge of the tail pipe, plus im only getting 18 mpg instead of the 22 was getting.

Thanks

At this point I would do a compression test on the cylinders.

good luck

I dont think im loosing compression, because it will haul butt if I give it just a little bit more gas. Seems it only does it when im in a situation that only requires the lease amount of pedal movement. What exaclty would a compression test tell me other than leak down? Oh yeah the engine only has about 50k on it.

Thanks

I don't know why, but something keeps telling me that the TPS is out of adjustment.

Not the normal way, though... I am thinking it is actually rotated a hair too far clockwise. You know, where the IDL signal is being sent when the throttle is just barely cracked open. The ECU is sending the right amount of fuel for idle, but it is getting too much air, leaning the mix out for that tiny amount of throttle applied. As soon as he pushes past that hair's breadth application, the TPS kicks in, and the ECU starts adjusting the fuel via the o2 and AFM signals.

The only hole in my theory would be the fuel cutoff... If he gets above 1800 rpm without brake application, the injectors would cut off...

Or would that be the cause of his "It does it every time if I'm coasting for a few seconds and then barely press the pedal it will surge like someone is holding a kill switch down and then it resume accelerating, this take place in just a couple of seconds."?

A compression test would tell the differance in compression between cylinder.
Idle would be rough with when a cylinder or two has low numbers, this may be due to a burnt valve or a headgasket that has been compromised between cylinders.

Also a weak fuel pump will produce a poor spray pattern at the injectors and result in unburnt fuel and poor idle.

But I would re-adjust the TPS, sounds like the timing is advancing a little late.

Good luck