Need help!
Wife's 97 ES300 (140k, great overall condition) has a check engine light. I'm pretty mechanical but am stumped on this one. Code indicates #4 cylinder misfire...that's it...nothing more specific. I have replaced plugs (iridium) and ignition wires. I swapped #4 and #6 coils to see if fault followed...it did not.

Now here is the strange thing. If cold, car starts and runs perfect with no light (presuming I cleared it). Runs great as long as you want. But, if you shut it down and restart it again within 5-10 minutes, in other words when it is hot, it has an obvious misfire and the check engine light comes on within a couple minutes. It has acted like this for over a month...exactly the same.

I have run concentrated Chevron with techron injector cleaner through a couple tanks with no change in symptoms.

Sadly, I live in the great state of California and I have only a month left until the registration runs out so I have to get on this...and I hate to give up and take it to a shop!

Any ideas out there?

One more thing that I forgot to add: if you start it when it is hot and the misfire occurs and the check engine light comes on, under hard acceleration the light will flash...but strangely the car will accelerate strong with no misfire. I heard something about closed loop and open loop something in relation to throttle position.

 

How long has it been since you've done some spark plugs and or wires? It sounds to me like it is just starting to misfire. It is rarely anything more than basic tune-up items on this motor.

 

I changed the plugs and wires about 3 weeks ago. Cleared the codes and drove it hard to test it...then drove straight to the smog test place where it failed....he gave it back to me chugging with the CEL. That is when I started putting together the symptom of it having problems after being started when hot. My wife said it did it after she got gas...well, when she gets gas she shuts if off to fill it then starts it. Since then I have tested my theory and it validates consistently. Ideas? I read something about the mass air flow sensor might need cleaning. I can do that, but why would that give a specific #4 misfire code? On one instance it gave a code of "several cylinders misfire" but only one time. Cleared it and it never came back...just the #4.

 

Yeah. A dirty MAF will most likely give you a "random cylinder misfire. If you've already done plugs and wires, and it drove fine for a while after you did that, it's got to be something else. cleaning the MAF is a good place to start.

 

I would check injector on that particular cylinder. It can be either spark plug wire, coil, plug, injector

 

My wife's 97 ES300 has exactly the same issue. She failed to mention the check engine light, but I drove it today and realized there is a random misfire on 3 and 5. I just had new iridium plugs and new plug wires last month. I took the car out on the freeway and after 20 miles, did a WOT wide open throttle blast, strong power nice run, but on idle, I can feel the misfires. I will go for the above mentioned cleaning routine when I have time. She's out of town, and use my RX, anyway. MAF has never been cleaned.

 

It is ether a bad coil or a bad injector.

 

Check the spark on that cylinder - remove the coil and measure it. You could have bad wiring or a signal issue.

Then I would check the injector pulse. It sounds like the engine is misfiri

 

Can you see any code ??

 

It was the injector! I changed out all 6 with remanufactured ones and the problem is solved! Thanks for all the help. All I have left now is a little whistle noise which tells me that something is either sucking or blowing (probably sucking?). I have been told to use brake clean on various suspect points to see if I can make the whistle stop and identify the spot. Any suggestions?
I plan to take it down to get smog checked today. Hopefully it passes and is good for another two years.

 

DJPsystems, you were correct, thanks. We did install all new iridium plugs, new plug wires, coils, still "random misfire on 3 and 5". Of course it had to be on the firewall bank and cost more for labor. I thought to myself, "Self, you must realize that at more than 140,000 miles, this is routine maintenance that you should have done anyway." So I told the shop, "Replace the injectors on that bank, so I don't have to pay labor again. PASS! Now it's time to move on to the next crisis.