Warm hesitation/stutter

I need some help figuring out what is causing my truck to hesitate. I have a 96 2.4l auto with about 110k miles on it.

On cold start ups the truck starts fine, idles fine, and drives great. The hesitation starts about 10 minutes later when the truck warms up. The hesitation happens with light/normal throttle after it shifts into second between 15-20 mph. It always happens right at that spot.

I have also noticed that at a certain throttle position, when held steady the truck will start to stutter. When going up a slight incline the truck will struggle and stutter.

The problems only occurs with normal throttle. If I was to drive it hard then I don't feel it.

On my last ecu reset I noticed that the truck would run perfect. No hesitation/stutter and the gas mileage seemed alot better. I also noticed that the gas peddle felt a lot smoother compared to when the hesitation/stutter is around then the peddle feels tight and rough. But after about 40 or so miles the hesitation problems all came back.

The truck has also has very bad gas mileage.

Things I have changed since getting the truck:
spark plugs- denso
Wires- ngk
Dist cap-Bosch
Rotor-Bosch
Pre cat 02-denso
Fuel filter-previous owner recently changed it

I have cleaned the maf, throttle body, iac valve.

I am thinking that it's either the tps, ect, or a clogged cat.

What do you all think?

 

Ive heard of this with a clogged cat. Cant say for sure. Check your fuel pump.
Have you tried running premium for a tank?

 

How do I check the fuel pump? Am I checking for voltage?

I haven't tried premium gas, I will on my next fill up which will be soon because this truck guzzles gas.

 

I believe you can check the fuel pump via PSI by hooking up a gauge to a valve at ther fuel rails. Not sure on the tacos though.
I found this guide. I cant guarentee it but there are a few do it yourself guides out.
http://www.ehow.com/how_4520277_check-fuel-delivery-toyota-tacoma.html

 

OK so after driving it yesterday and today without changing anything, I am having the hesitation during the warm up instead of when the truck gets to full "warm" normal temps. So after letting the cold engine warm up for about 3 mins I drive off taking it easy and about 5-10 minutes into it it starts to stutter and hesitate. Again it happens after shifting into 2nd (auto trans). It will mostly do it after that 2nd gear.

When the engine gets what I am thinking is "fully warm" and up to normal operating temp, the hesitation goes away and the truck drives proper. The throttle feels a lot more responsive and overall great.

Now what could it be? Ect? Thermostat? Egr?

Any help will be grateful. Thank you.

 

Bad thermostat causing the engine to think it is not warming up, therefore making it run rich and burn more gas? I have no idea really, but I did stay at a holiday inn last night

 

Have you checked the voltage between you cats for the o2 sensors to see if they are switching at the normal rates. I believe you have a cat on its way out. Another way to test this is use an infrared temp gun. If the post temp is say 375 and the exiting temp off the cat is 390 the cat is not working the way it should. If the cat is bad why did it go bad? Check for misfires and any large vacuum leaks

 

I put in an new pre cat 02 sensor about a week ago. It made it better. I will check the post cat 02 and see if I can find someone with a infrared temp gun to check the temps.

 

OK so I checked the temp of the catalytic converter with a infrared thermometer. Inlet is 400f and outlet 460f.

Also lower Rad hose temp at Tstat reads 150f and upper hose right at the radiator is 140f. Is that about right? This is after driving in traffic for about 15 minutes.

 

So I've had this sporatic stutter starting back in Sept. First it happened while idling. Then on the highway crusing at 60-65mph. Couple of stutters then smoothed out. Took it to shop and they did not find and CEL codes. PCV valve good, no leaks or other issues found. They recommended a fuel system flush and to change spark plugs based on age and milage. I had them do the fuel system flush (which was probably a waste - seems like a scam) and I did the spark plugs because I was just about due anyway. Truck had about 98,000 miles. Still stuttering - so I ran a couple tanks of 93 octane and the stuttering stopped for about a month. Figured I was in the clear and that it was probably a bad tank of gas causing the problem. Now I am back to 87 octane which I've been running in the truck since new and I am getting the stutter back again after only it did not return right away after going back to 87.

What else could be the problem? Could it be electrical/computer related? Almost seems like it is searching for a gear - transmission? I've also done the ATF change hoping that would help. (I know there is a specific procedure to follow and has to be done at correct temp - I followed the procedure successfully).

Maintenance in order:
MAF cleaned
Engine air filter changed
No CEL codes
System pressure checked
Fuel system flushed
Spark plugs changed
2 tanks 93 octane
Fuel stabilizer added to 1 tank of 87
ATF changed

Next: ??
fuel filter
fuel pump
timing chain check
reflash computer
??
??

 

help!

 

Still need help. It was running rough at idle last night, not even in gear. Can't be transmission or anything drive train related. I'm due for emissions test so hopefully that will tell me if the cat is bad or o2 sensor.

 

this gremlin is being chased by many and there is no smoking gun to point to but you did what needed doing first so now it comes down to poor fuel pressure from a fuel pump issue of a clogged cat.

I don't see fuel pressure making much sense in these cases so look at your cat, it may be full of soot and not flowing freely causing too much back pressure.

by the way I have the same exact thing going on and cant find a solution either but my intake manifold and EGR was heavily sooted up so I bet I have a clogged cat as well but I don't have a temp gage to check it.

 

So the shop said they found the problem. It was a misfire on cylinder #5. It was only misfiring 10 times out of 9000 cycles so it wasn't enough to triggle a CEL. Anyway, they replaced the spark plug coils on that cylinder and it was still misfiring so they replaced the injector. Problem seems to be solved now but I've only driven about 50 miles since it was fixed.