help with throttle problem that turned into a misfire... - Lexus IS Forum
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post #1 of 7 (permalink) Old 05-09-2019, 08:17 PM Thread Starter
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help with throttle problem that turned into a misfire...

So most of this is a really long story, but I will give the spark notes and get to the issue...

I took my 03' to a mechanic to do some warranty work for an oil leak on the vvti cam gear. he never could get it to run right after he worked on it, and stupidly I bought a used TB because he said it would fix the issue. once I got it back all it would do is run in limp mode, and I ended up limping it home. (yes now i know the mechanic is a hack, and trying to get them to cover anything is going to be next to impossible..)

I originally had a bunch of throttle body codes. TPS, APPS, all that stuff. The connectors ended up being pinned out incorectly, as the mechanic had broken the connectors and tried to just put the wires on the terminals.

I have since figured out how they were supposed to be pinned out and replaced the broken connectors hoping my problem would be fixed. Once I fired it up I got codes saying the TB was stuck closed.

At that point I took the TB off, and replaced it with the original TB. It worked for a short moment, and suddenly im getting misfire codes. P300, P301, P306 that were never there before.

to finally get to my actual question, It looks like he just slapped a bunch of silicone all over the cam gear to fix the leak, and it looks like he may have taken the cam gear apart and put silicone there too... obviously that is a no go, as the dealers dont even fix those, but throw them away if they've been taken apart. If he did actually take it apart would that cause a misfire?

This whole time I have been focusing on trying to get rid of TB codes before I would worry about the hackjob on the cam gear but Im begining to think he mixed the wires on my TB on purpose so that the car being in limp mode would hide the misfires...

Im super lost at this point and dont really know how to proceed. should I chase a misfire, or start with replacing the whole cam gear?

also, when I turn on the car initially it runs OK. idling the CEL is on, but if I give it throttle it turns off. Then after about 30 seconds it throws it back to limp mode with the misfire codes.

Thanks for any help.
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post #2 of 7 (permalink) Old 05-10-2019, 08:52 AM
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Multi-faceted problems are always the most fun to sort out!

I know the Toyota manual says the VVTi gear can't be disassembled or serviced, but that's BS. I've taken both of mine apart, installed the new O-ring, reassembled and went along my way with a happy engine. It's true you lose the magic "laser alignment" that Toyota did at the factory, but there is no way you're going to screw it up more than 1º - and that's if you DON'T bother scribing your own alignment mark on it. 1 or 2º of intake cam "out of phase-ness" (if you will, lolz) is NOT going to cause misfires.

So, fix the hackjob on your VVTi gear, or buy a new one if makes you feel better.

Next, regarding your DBW throttle problems. You need to go back through the pinout of all 3 of the connectors and really, really satisfy yourself the wiring is correct. Also inspect each female socket terminal in those connectors to be sure it is getting a good connection onto the pins on the throttle body itself. If no issue there, you'll need to follow the diagnostic and wiring manual available for these cars and go wire by wire, checking their voltage. The manual tells you what all readings you should be getting.

Seems to me you've now had two throttle bodies that don't work - which is either a huge coincidence, or points to a wiring issue.

So our old engine harnesses don't age well, and the get pretty crispy. You need to inspect all the wiring and connectors anywhere near the throttle... Like, for example, the COIL connectors directly under it. They are notorious for breaking, and bad connection to your coils could most definitely cause misfire.
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post #3 of 7 (permalink) Old 05-11-2019, 09:43 PM
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That vvti should be a quick fix there are videos on YouTube about it the seals can be found for a little bit of money on eBay. Just get some towels and do it when you change your oil to minimize the mess. Good luck to you
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post #4 of 7 (permalink) Old 05-14-2019, 08:31 PM Thread Starter
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Thanks for the advice! so a bit of an update,

I had a few minutes yesterday to take a look at it and there was a ton of oil in the sparkplug wells from my valve cover leaking. My coils tested good but I didnt have time to actually test the spark plugs. Hopfully this weekend I will have the opportunity to take it apart and really clean the oil out of there. Im hoping once its all clean it will fire up right.


Also I noticed a little bit of fuel leaking around one of the injectors of the misfiring cylinder, could this be a clogged injector? or just a bad seal?
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post #5 of 7 (permalink) Old 05-15-2019, 07:53 AM
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Start from scratch. Forget everything that happened (to a point)
I would check the basics and go from there. Spark, fuel, compression.
When you add all these variables you're just adding to the confusion
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post #6 of 7 (permalink) Old 05-15-2019, 02:53 PM
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Quote:
Originally Posted by whitedragon77 View Post
Thanks for the advice! so a bit of an update,

I had a few minutes yesterday to take a look at it and there was a ton of oil in the sparkplug wells from my valve cover leaking. My coils tested good but I didnt have time to actually test the spark plugs. Hopfully this weekend I will have the opportunity to take it apart and really clean the oil out of there. Im hoping once its all clean it will fire up right.


Also I noticed a little bit of fuel leaking around one of the injectors of the misfiring cylinder, could this be a clogged injector? or just a bad seal?
It will. May not be the only issue.

Careful & Consistent
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post #7 of 7 (permalink) Old 05-16-2019, 08:04 AM
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Oil in the spark plug valley will make the engine misfire. Replace your valve cover gaskets and reseal your injectors, although if I had them out like that I'd get them flow tested and/or cleaned too.

02' MT w/MK3 Supra LSD and no sunroof
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