2003 Toyota Tacoma hesitation rough idle

hi all.

Truck has 197,000 miles on it. In great shape. All stock. Well maintained. Ran perfect for years.

Pulled out in front of a car the other day. Floored it to prevent from getting ran over. Truck immediately started hesitating and stumbling. Like it dropped a cylinder. CEL came on while on the way home. Flashed for a while. Stored a code. Misfire on cylinder 4.

So. New plugs. New wires. New coil packs. New pcv. New factory injectors. New fuel filter. Compression test was good. Cleaned the throttle body with sea foam. Put noid lights on the injector harnesses, no problems there. Cleaned air filter. Check air box for clogs. Still throws the same code.

Only cylinder 4. Seems like it is just something localized to that cylinder? But the symptoms I am having seem like a bad throttle position sensor. Rough idle. Slow acceleration. Low power. Slow shifting.

Thanks for any input.

 

Switch the injector with another cylinder, see if the problem follows the injector.

 

possible carbon build up if everything else turn out ok. (just throwing it out there)

 

I tested the old injectors with a multimeter. They checked out good. Figured maybe it was a mechanical failure and not an electrical. So I replaced the old injector with a new one. Didn't help.

 

Could a bad throttle position sensor cause a misfire on just the number 4 cylinder? Seems like a bad tps would cause multiple misfires?

 

New issue.

With key turned on, but engine off. There is a loud mechanical buzz/humming coming from the throttle body. When I rotate the throttle body lever that pivots the door that lets air through, the sound gets worse. Almost like a electrical short/mechanical grind noise. Hope that makes sense.

 

Bump

 

Did I post in the wrong section of the forum?

 

No, no one is answering thats all. A buzz from the throttle body? only thing I can think of is the throttle position sensor, or idle air control valve. Ive heard taking off the iac and cleaning it does wonders for rough idles. My model (2004 dc v6) doesn't have an iac. And I've been pulling out my hair trying to diagnose my rough idle. Cleaning it is fairly straight forward ive read, and cheap as you only need cleaner and a cheap gasket.

 

Thanks roehoe72 for the reply.

I've cleaned both the tps and iac area.

I'm in the same situation also with the iac. Odd they changed it.

I also have a 4 pin tps. Instead of a 3. I'm down to replacing the tps. Just don't make sense to me. Seems like a bad tps would effect more than just one cylinder (in my case cylinder 4). Maybe certain areas of the tps get scarred/worn more than others? No idea. I will replace it and let you know.

Have you done a recent tune up? What have you done to fix you idle problem?

 

I never had a bad hesitation like you. My only problem is a rough idle when i pull up to a stop sign /light. I did a full tune up. Plugs, wires, fuel filter, oil filter, air filter, cleaned the throttle body, cleaned the maf, tranny filter. Even cleaned the egr valve body solenoid things. I don't have an egr valve. My next step is to replace ALL vacuum lines. I even water decarbonized the pistons. Seafoamed the oil, fuel, and pistons also. Here is the thread i started.

https://www.tacomaworld.com/threads/rough-idle.365671/

 

Thanks again for the input and the link. It re assured me of the differences in this year model truck. Like no iac and the Electronic throttle control system.

Learning about the etcs has helped. My throttle body buzzing humming sounds like a motor glitching out. I ordered a newly used throttle body with all sensors in it. I will let you know when I get it the results.

Btw I also sea foamed through the pcv vacuum hose. Didn't help.

Wonder is a defective tps or isc can cause a etcs to malfunction? Like cause the tb plate to fault and open and close a little while running and let the wrong amount of air through?

 

the tps is the main culprit for hesitation or throttle position things because it is supposed to "smoothly" change resistance but if its bad it gets jumps or spikes in the readings and the ECM takes that info to respond so while nothing is for certain you will probably need the TPS but test yours first by putting and ohmmeter on it and as you turn it you should see smooth steady change in resistance and no twitchy readings or skips.

you might be able to use this one: http://www.ebay.com/itm/191573212874?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1555.l2649

 

Fixed!

Started the process of fixing my problem off by swapping a known good plug wire with the one on the misfiring cylinder. Didn't help.

Replaced plug. Didn't help.

Replaced pcv valve. Didn't help.

Cleaned throttle body and sensors. Didn't help.

Replaced injectors. Didn't help.

Noid light to all injector harnesses. Worked great.

New coil packs. Didn't help.

Seafoam through vacuum lines. Didn't help.

Thought maybe a stuck valve or burnt valve. Decided to start the whole diagnosis process over again before taking the truck to the shop.

Cleared all codes. Switched plug wires again. Plug wires had less than 8,000 miles on them. To my surprise. This time the code thrown changed cylinders for the first time. I reinspected the plug wires. The boot was completely cracked and firing the spark out the side of the boot before it was getting to the plug. Making the the truck run rich. Obviously when I first tested the wire the damage was nearly unnoticeable. As I worked on the truck and test drove it over and over. The truck ran worse each time. Guess the wire was getting in worse condition.

Anyway. Massive tune up. But it didn't hurt being the truck had 200,000 miles on it. It's usually something simple when your well kept Tacoma has a problem.

 

wow, that's an easy one to never notice, who thinks about that part and yet its under a lot of abuse installing and removing it

 

Yeah really. Odd thing was. The code never changed when I first swapped the wire. But thinking back. I had not replaced the plug at that point. Which looked very fouled on cylinder 4. Plus I didn't throughly inspect the wire. Being I just replaced them new 8 months prior.

It really runs like new now. Hoping for some mpg gains. Thanks for everyone's help.