P0300 P0302 P0303 1998 Toyota Tacoma Prerunner

Thanks in advance for all the help folks...

I have a 1998 Toyota Tacoma Prerunner. It is the 4-cylinder model. 2 weeks ago it started shaking here and there, but not very noticeable. Finally a week ago it was shaking very bad and the check engine light came on intermittently. When I first start the truck it runs fine but after a few blocks of driving it starts to shake and the check engine light comes on. I pulled the OBD2 codes and it gave me a P0302 code (cylinder 2 misfire).

We did some basic troubleshooting, and found a couple cracked vacuum lines which we replaced. At idle we noticed it was going back and forth form running smoothly and then shaky. I have a mechanic acquaintance who works at a Toyota Dealership look at it for me and he could not find anything. I forced him to look more in depth and this is what we found:

Timing - Good
Cylinder compression - Good
Cylinder 2 Running 5% - 33% off normal (0%) - Im not sure what this reading checks but it was going from 0 then to off...

I was thinking it could be the coil pack. My truck is distributer-less and has 2 coils for cylinders 1,4 & 2,3.

I switched the coils to see if the code would jump (indicating a bad coil pack) but that didn't change anything.
We checked the spark plugs, and they were fine, but we replaced the spark plug for cylinder 2 anyway with the suggested spark plug for my vehicle. The truck took a little longer to start shaking but it still threw the code. I put fuel injector cleaner in because I was thinking it could be the injector. Still problems...

For the last 3 days it was driving more smoothly, but just today it started shaking very badly. We pulled the codes and now it is showing p0300, p0302, p0303 and another one indicating lean fuel mixture (most likely caused by the misfiring). Keep in mind I still have the coil packs reversed from when it originally threw the p0302 so it is not the coil pack. I believe cylinder 2 is having the most trouble but I cannot figure this out Please help!!

Other considerations: Some scumbsack stole my Cat Converter last Thanksgiving so I had a brand new one welded in its place. I changed the oil a month before the trouble started. Compression is good, no known fuel problems. No other known problems or maintenance deficiencies.

I'd start with 4 new plugs! Are they original? What's the mileage on the truck? is the timing belt still lined up correctly? Is the truck equipped with an EGR?

As Jeff said, and Check that they were not BOSCH plugs they will give you that same problem seen it lots of times.

Thank you for your replys. To answer a few of your questions, the truck has 149,000 miles on it. The timing was checked by the toyota technician and he claims that the timing was perfect. He also said that the cylinders have perfect compression also. As far as the EGR, I would have to look it up, Im not that mechanically inclined, but Im fairly certain it does, and the vehicle should throw a code for the EGR if something was wrong with it AFAIK. As far as the spark plugs, I do not know which brand, but they very well could be bosch. I didn't pry too much cause the tech put a brand new one in for free so I didn't want to gripe about brands at that point. I am almost wanting to just go ahead and change the plugs and plug wires any way, although they aren't that old.

AN update of what I did today:

Some other forums suggested that I check the MAF Sensor, which I did and it was somewhat dirty so I cleaned it with MAF cleaner. I also injected some carb cleaner into my throttle body because it was in deed somewhat sticky. I also ran some fuel treatment and fuel injector cleaner. After we did the throttle body cleaner, the truck seemed to run very smooth especially at idle. Sadly the problem still persists as of my drive home from work. I found the FSM for my truck so I am going to have my mechanic friend look at the wiring diagram for ideas. He seems to think that the problems source is before the coils. I believe I mentioned that we checked the wires OHMS and they were satisfactory. If I go ahead and replace those and the plugs, what are the recommended brands to use and any possible locations for best deal would be greatly appreciated. Apparently Bosch plugs aren't desirable???

Another test someone mentioned to me is to spray the engine with a light mist of soap and water at night near the plug wires and check for arcing?? Is this a viable method to test this and how do I perform this check properly? I actually heard it from 2 separate people with no relation to each other whatsoever.

What does anything think about a possible bad injector???

An ohms test on a static ignition wire is pretty much useless in my opinion unless it confirms that it is in fact open. I disagree about the egr but Im not going to argue it at this point. I've seen enough misfires caused by egr's with no egr codes on mazdas, dodges etc to know it's a possibilty. If I were you I'd get your buddy to get you a good deal on ign wires and plugs from the dealer he works at and start there. If it were an injector why more then 1 cylinder? You're test for a poor ign wire is still a good test but again it's not always 100% accurate! I'd still recommend the dealer stuff for the parts. Why don't you just have your friend fix it?

UPDATE:

Ok folks. I replaced the Spark plugs and spark plug wires to NGK Iridium and NGK wires. The old wires were Denso and the old spark plugs were as well, but they were just regular plugs. Any way I have new wires and plugs and the problem persists. We know it is not the coil packs because we switched them out and the CEL still threw codes on the original cylinders (2 (and now 3 also)). We checked compression which is fine (so its not a burned valve), timing is fine, its not the EGR because that would throw its own code (actually I checked and this piece was replaced not too long ago anyway). We are almost certain it is not an injector, especially because it is throwing the code on two cylinders now.

Here's where my biggest focus is. The cylinders that are misfiring are two and three. These both share a coil pack, but we tested it and found it not to be the problem. The only other thing that it shares is the pigtail or wiring connection. Therefore I believe it is something to do with the signal coming from these wires. Now with my prerunner, the igniter is in the coil packs, so the question is where do these wires go?

Does anyone have a wiring diagram for a 98 prerunner? OR 98 Tacoma with 3ZFE 2.7 Liter Engine (4 cylinder)? There could be a component that shares these wires that is defective and causing this issue?

Another item to note: I have a diring diagram for a 97 toyota 3zfe engine that shows the coil packs 2 and 3 sharing a common ground between 1 and 4. The interesting thing is that it shows to other wires going to a connection (perhaps on the ecu?) labeled as "oil". Now supposedly 98' started a new model so I need a 98' wiring diagram to make sure they didn't change the wiring for this year. BUT, interestingly enough I did have my oil changed by god forbid Walmart about a month prior to the start of the misfiring. Perhaps it is an odd coincidence, but there could be something here. Any ideas????

New or not very well expressed symptom: Some times, when it is not shaking like a red headed stepchild about to be punished by his biker step dad, I will have my foot on the accelerator and it will feel like Im getting a major boost for a second and then it will calm down again and shake.

Yes I have four new NGK Iridium spark plugs AND new wires. The truck has 149666 miles on it, and the timing is good. It does have an EGR which has been replaced somewhat recently as I can tell from the newish gasket and vacuum line attached to it. The EGR should throw its own code if there was a problem with it AFAIK

your buudy the toyota tech should have the wiring diagram. as would a haynes or chilton manual would. I think you're in over your head at this point

Well I believe my problems have been solved. For those interested heres what I found:

We performed some simple OHMS testing on various vehicle components. We found that we had an injector that was way outside of the OHMS parameters. Normal resistance for my injectors was 13.5 Ohms, and my number 2 injector was at 43 OHMS. I replaced the injector and cleaned out the throttle body with carburetor cleaner while it was open, along with the other injectors. A few hoses cracked during the operation so I replaced those, and took out the FRAM oil filter and replaced it with a much much better one. Now the vehicle runs smooth as silk.

SO I should be done with my problems for now. Just remember that if you can't solve the problem with simple troubleshooting, get an electrical wiring diagram and do some resistance testing on your components!

Thanks for all who helped me along the way. And a special shout out to Cannon Automotive of Sacramento for the help and use of equipment and testing tools. Excellent work from this man!

As lots of misifre posts in these forums can confirm switching an injector from a misfiring cylinder to an adjacent and seeing if the code moves is a test that can be done with no specailized tools other then the code reader that you're already using. Just something for everyone to keep in mind for future. Congrats on the successful fix. 43 ohms is alot though compared to the rest of them at 13.5!