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Toyotapro, ASE master tech
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I have a 97 toyota 4 runner with an intermittent misfire.

Resolved Question:

I have a 97 toyota 4 runner with an intermittent misfire. The first time, check engine light came on and the mechanics told me cylinder 6 was misfiring. They replaced spark plugs and ignition cables but it didn't solve the problem. So then they say I needed to replace the fuel injector for cylinder 6. I did, and now I'm $1000 deep. So it ran great for a month, then engine light back on and the misfire. The code, according to the mechanics was now cylinder 4, but they said they could find nothing wrong, and the vehicle ran great for them.
They reset the check engine light. The vehicle ran great for short trips, but after a 30 minute journey, check engine light and mssfire again. Next day, it drives fine, check engine light off by itself, but vehicle will begin to misfire again after 30 minutes and be fine at cold start. What the hell should I do? I am reluctant to take it back to the same mechanic.
Submitted: 7 years ago.
Category: Toyota
Expert:  Toyotapro replied 7 years ago.

Thank you for using just answer. Sorry to hear of this issue.

Is this a shadetree mechanic doing the repairs or is this a dealer?

If not a dealer- do you know what BRAND plugs and wires were installed on the truck?

Customer: replied 7 years ago.
Not a dealer, just a local garage. The wires that were installed are NGK. I dont know about the plugs.
Expert:  Toyotapro replied 7 years ago.
Would be very helpful to know about the plugs....
Customer: replied 7 years ago.
Ya, don't have the tools to pull plug out. I tried to have a look but I need to take it out to identify. I can call and ask the mechanic tomorrow. Should I just resubmit my answer tomorrow? I also forgot to mention that they also performed a fuel system service. So maybe you could advise me know, should I take it back to the same guys? It seems to me that they are part replacers, not able to find the real problem.
Expert:  Toyotapro replied 7 years ago.

Kind of my feeling as well....there are a few common issues that can cause this but that is why I am asking specific questions here.

First check the spark plug condition and brand- certain plugs such as BOSCH commonly used by aftermarket shops are NOT good on toyota engines, i only recommend that NGK or DENSO brand plugs (just standard or platinum) be used on this engine, I get a ton of intermittent misfire issues in my shop related to junk spark plugs.


Second if this still is an issue the coils and fuel injectors need to be checked, I see some issues with obstructed fuel injectors on these sometimes, if this was an issue with a primary sensor or another item you would have misfires on multiple cylinders.

Customer: replied 7 years ago.
So if there was misfires on multiple cylinders, would that be happening at the same time? Because the first time it was cylinder 6, the second time was cylinder 4, but not at the same time.

Also, why would the check engine light go off by itself, but then the misfire continues once the engine runs for 30 minutes? for the time being, is it ok to drive the vehicle when it is not misfiring?
Expert:  Toyotapro replied 7 years ago.

It is ok to drive with no misfires, it is not ok to drive with misfires.

If the issue and the light come and go this is an intermittent issue such as a restricted injector or a plug quality issue. There are 6 injectors on this engine, the cleaning may have knocked deposits loose and now causing issues.

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