coastierider

2005 Scion TC
Base/Manual Trans
108,000 Miles

Symptoms: Severe Engine jerking/shuddering at 75+ mph, gets worse as speed/RPM increases. Symptom occurs under load only after reaching operating temperature.

Suspect Causes: Spark Plugs, Ignition Coils, Dirty Fuel Injectors, Fuel Filters, O2 Sensors, Clogged Catalytic Converter

Completed Steps:
Step 1: Installed K&N high flow air filter
Step 2: Replaced Clutch (Not related, it was worn out anyway)
Step 3: Cleaned MAF sensor
Step 4: Checked to ensure no loose vacuum lines
Step 5: Replaced 04 spark plugs
Step 6 Removed, cleaned, and reinstalled throttle body
Step 7: Removed, cleaned and reinstalled all fuel injectors
Step 8: Replaced both In-Tank fuel filters

To Be Completed:
Step 9: Checked resistance on both O2 sensors.
Step 10: Use IR thermometer to get inlet and outlet temp of Catalytic converter.


There was a similar thread a long time ago that pointed to the Catalytic converters as well:
https://www.scionlife.com/forums/sci...tutter-168353/

I'm hoping to do a little more testing before replacing the Catalytic converter/exhaust manifold.

Do you guys think I might be missing anything?

TheManinDboX

I would suggest starting out cheap..
Since you Replaced all the plugs, make sure they are gapped correctly.. Even though they say Pre-Gapped on the box, don't trust it, it's generally off a little..
Replace the fuel filter, there should be one under the hood, make sure the battery is disconnected, and wait a good 3-5min before you start to pull the filter, it's under pressure, so make sure you wrap it in a towel before you pull it out of inline.. If you are quick, you can change it without making a mess.

I had a similar issue on my corolla, which turned out to be bad plugs and a clogged fuel filter.

coastierider

I checked the gap before installing the spark plugs, the fuel filters are all located inside fuel tank as per factory service manual. The ECM has already been reset, while I was cleaning the throttle body.

sciontc_mich

I'd suggest you check the ignition coil packs, it's in the factory service manual how to check them. I believe it's a resistance check. I've heard of some of the 05's going bad. It's hit-miss.. They usually last around 100k miles before they begin to die. Check that.. If that passes all the tests, might want to start looking at the catalytic converter.. we have two from the factory, one up on the exhaust manifold and one downstream in the b-pipe/intermediate pipe.

I'm going to bet it's the coil packs that are causing this stutter, because if a cat is plugged, it wouldn't be stuttering, you wouldn't be able to get up to any high speed (not being able to exhaust would limit intake).

coastierider

I was looking through the FSM, and could not find a resistance check on the coil packs. The only check for them I found was to remove the spark plugs from the engine and turn the engine over and make sure there is spark. There is a voltage check on the wire harness which I will check. Since I got the mutlimeter out I'll go ahead and check the resistance on the O2 sensors.

coastierider

The coil packs checked good as per the FSM, but the A/F ratio sensor was reading resistance beyond normal, so I replaced it. No luck I'm going to check all the ignition connections again

bbsciontc

Not to send you on a wild goose chase, but also check the crank and cam position sensors. Since they control ignition timing, an issue with either can cause symptoms like that as well. The FSM has fairly simple resistance checks for them too.

coastierider

I already checked the Cam Position sensor (good) Haven't done the cranckshaft position sensor yet

coastierider

Replaced all 04 coil packs. No luck, symptoms continue

sciontc_mich

looks like it might be time to take it to a knowledgeable shop that can diagnose what's going on with their diagnostic equipment. I would say a dealership but I know from personal experience that some dealerships are not that knowledgeable. (just parts replacer's) I say a good shop because you can't just keep throwing money/parts at this, it's best to get a good shop pay them to diagnose it and find out 100% what it is. The other thing is if the coil packs aren't toyota that could be the problem too. People here have replaced 02 sensors, for example, with aftermarket versions and they did not work correctly. but my thought of a good shop still stands..

coastierider

**Update**
3/12/16
Code: P0340
Camshaft position sensor/ sensor bank 1

Replaced cam position sensor - Negative Results

burgandybomber

iTrader: (1)

I second this only because I too have played the "throw parts at it till its fixed" game. If the symptoms get worse as speed increases, you may be looking in the wrong place. It is possible you have a brake/steering/mount issue. All of your possible suspects seem like they would cause lack of power and breaking up and would be noticed well below 75 mph but it is still odd to occur under load at operating temperature. When my main O2 sensor when out I had an excessive lack of power at any RPM (as a matter of fact I could barely get up to 45 mph). Also, I don't think any state has a speed limit over 75 . Good luck!

coastierider

**FIXED** Crankshaft position sensor was occasionally shorting out on the engine block, when i checked the resistance a few months ago, the resistance was within imits because it wasnt actively shorting out when i tested it.

burgandybomber

iTrader: (1)

Good job finding the cause! Not many people around here who actually post up with issue resolution. Thanks for the contribution!