Misfires, rough idle, shaking

Tiny
ACORN8
  • MEMBER
  • 2000 TOYOTA 4RUNNER
  • 3.4L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 314,000 MILES
Am I getting ripped off? Third Gen. Toyota 4Runner misfires, rough idle, shaking (details below)

My car was running just fine a year ago, when I went to a highly rated (Yelp and Google Maps reviews) independent shop because I noticed the red brake light on my dash coming on sometimes. They fixed it by tightening something, no charge, but also talked me into doing a tune-up (oil and air filter change and replaced spark plugs and wires - $350.00).

Ever since that day, my car has been shaking upon startup, while accelerating and while sitting at stoplights, but shaking goes away at cruising speed. Check engine light is also on. (What could they have done to my car to cause this problem?)

I immediately took it back, and they said “oh, it turns out we put a defective part, but we replaced it with a new one”. No difference – problem still there.

I took it back, they pulled codes P0300, P0303, P0306 (random misfires). They replaced wires under warranty, replaced radiator cap, and swapped ignition coils to test misfire. Maybe put one new ignition coil. (I paid $180). Also suggested I add Techron to my tank next time I fill up. Did that, twice, floored it while accelerating through two tanks of gas. No difference – problem still there.

Went back again, they pulled codes P0300 and P0304. Replaced 1 spark plug. (No charge). No difference – problem still there.

Had Auto Zone pull codes P0300, P0301, P0303, P0304 and P0420 (Catalyst System Efficiency Below Threshold – Bank 1).

Had problem diagnosed at Toyota dealership (they’re the experts on Toyota's, right?) – They wanted $2,000 to replace fuel injectors and $150 to diagnose “excessive coolant loss”. Also suggested another tune-up for $170 because they “Found engine to run rough” – well Duh – that’s why I came to you and I told you I had a tune-up 6 months ago! (Paid $140 for diagnosis and left).

Went back to independent shop, pulled codes P0300, P0301, P0306. They replaced fuel filter and did Air Intake Decarbonization Service – BG. (Paid $280.00). No difference – problem still there.

Went back again – now they want to replace fuel injectors, seal kit and intake plenum gasket – quote is $733.00 plus tax.

My own research on the net suggests ignition coils may be the problem? (A much cheaper fix). I already replaced the Mass Airflow Sensor a few years ago.

I want to trust these guys – they seem like good guys, but it seems to me no coincidence that the misfire/rough idle problem started immediately after they did their tune-up, and now I’ve given these guys over $800.00 and the problem has not been fixed, and they want another $733.00 plus tax…

Obviously it’s an old car and every part is getting old - I figure I can afford to replace parts as they fail – but I can’t afford to replace every part on the freakin’ car in a wild goose chase to fix a problem – shouldn’t they have been able to diagnose this and fix it correctly by now for much less money? Doesn’t it seem like maybe they caused the problem in the first place in order to sell me all this service? Shouldn’t they refund me what I’ve paid so far so I can afford to replace the ignition coils and/or fuel injectors and finally be done with this problem?

What should I do? What would you do? Thank you in advance for your advice.

Year 2000 ("third generation") 4Runner, SR5 2WD, 183-hp, 3.4-liter, V-6 engine, regular gas, 19 MPG (combined), fuel-injection, non-interference, four speed automatic w/OD ECT transmission, California emissions, 314,000 miles.
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Tuesday, September 10th, 2019 AT 9:31 PM

5 Replies

Tiny
SCWICKEDSTANG
  • EXPERT
Hello,

I understand that chasing gremlins around with driveability issues can be very, very, very frustrating. Random misfires can be caused by a lot of things, so we will be running down a list of things, the most likely culprits to the least until we come across the problem, or problems, okay. I know you're probably fed up with the whole thing and looking for somewhere to buy a stick of dynamite, but please, have a little patience and we will get everything worked out. Okay, so let's check on the health of the engine real quick with a compression test. This will give us clues to the health of the piston rings, valves, and head gasket of the engine, rule out internal engine failures and is fairly cheap and simple to do. You will need to have a compression gauge, which can be purchased at any auto parts store for around $20.00 or rented by just leaving a refundable deposit. Here is a link describing how to do a compression test below:

https://www.2carpros.com/articles/how-to-test-engine-compression

Please go through this guide and report back with the readings on all 6 cylinders and we will go from there.

Thanks,
Alex
2CarPros
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Wednesday, September 11th, 2019 AT 3:14 AM
Tiny
ACORN8
  • MEMBER
Okay, thanks so much Alex - will do and get back to you.
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Wednesday, September 11th, 2019 AT 7:46 PM
Tiny
ACORN8
  • MEMBER
Alex - OK, did the compression test (dry test), readings were as follows:
Cylinder 1 - 180
Cylinder 2 - 180
Cylinder 3 - 175
Cylinder 4 - 160
Cylinder 5 - 180
Cylinder 6 - 175

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Sunday, September 15th, 2019 AT 8:10 PM
Tiny
SCWICKEDSTANG
  • EXPERT
Hello again,

They all look good to me. Pretty strong actually. Cylinder 4 so/so but still very good readings as a whole. Okay, now that we know it's nothing internal causing these random misfires, normally I would go the ignition system, i.e. spark plugs, plug wires, ignition coil(s), but the problem with that here, is that you are having misfires on ALL of your cylinders at random times with no rhyme or reason to it. That would lead me to an air intake or vacuum leak. Next lets check to make sure no unmetered air is getting introduced into the engine, i.e. let's check the intake manifold gasket. Okay, so a vacuum leak and unmetered air is described as any air entering the air intake system up to the engine's combustion chambers that enters past the Mass Air Flow sensor(MAF). Since you are experiencing multiple random misfires this is the likely culprit. It would also produce rough idle and low speed driveability concerns and would smooth out at higher speeds because of the volume of air being ingested by the engine. Down below is a link explaining how to test for a vacuum leak. Please pay close attention to the intake manifold gasket area.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

I have also included an exploded diagram of the intake manifold and associated parts in the diagrams down below to help you. Please get back to us with what you find out, and we can go from there.

Thanks,
Alex
2CarPros
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Monday, September 16th, 2019 AT 1:28 AM
Tiny
ACORN8
  • MEMBER
Thank you - very encouraging! Will get back to you.
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Monday, September 16th, 2019 AT 10:33 AM

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