Fixed my 2000 Sienna, was running badly

This is a bit long winded but I hope story helps others troubleshoot their issues even if it's not exactly like mine.



The 2000 Sienna with a 1MZ-FE engine that I've owned since 2004 began to perform pooly. It had been running fine for years, then within a few weeks started having issues. Running rough, hesitating, drop in gas milage, hesitant/rough shifting and a heavy throtle caused a growling noise with very weak acceleration. The problem was oddly pedal position dependant. It would actually start and idle just fine too. So after a couple weeks of study and repairs I though I'd share the my own results since I had trouble finding other helpful post with my specific problem.



Initially the only code that was read said that cylinder # 4 was misfiring. My first thought was maybe we got a bad tank of gas. After a couple of fill-ups, the trouble remained, so poor fuel was eliminated. I changed the old and clearly worn out spark plugs and wires and cleared the codes. But the poor performance remained and within a couple of days the same single code on #4 returned.



The interesting symptom was that the van ran pretty well if the pedal was not pressed past a certain point. You could press on the pedal quickly or slowly as long as you didn't press it passed a specific point. If I pressed just a bit more, then the rough running returned. If I let off a little, it ran fine again. The TPS ( Throttle position sensor ) seemed a likely suspect at this point. It's position sensitive and I've found bad ones on cars I've owned in the past. I was going to pull the TPS off and test it. Unfortunately I found the screws holding it were stripped. A previous owner/shop must have damaged them in some earlier repair. Believing it was probably bad anyway, I broke it off and then was able to grab and remove the screws with pliers. I put nice new screws back in when done.



I also decided it was time for a new fuel filter. So with new TPS and filter installed (about $60 total), I thought I should be good to go now. Not so. It ran a tiny bit better and I attributed that to replacing the very horrid looking fuel filter. But some thing was still wrong. In thinking through all the possibilities and looking at all the online diagnostic info, several possibilities remained. O2 sensor, EGR valve, EGR solenoid, fuel pump, head gasket, leaking cylinder, ignition coils, computer module, vacuum leak, transmission failure.... the possibilities and price tag seemed likely to soar. I began to narrow the list by eliminated the things that should throw a code, but did not... O2, EGR-V, EGR-S all off the list (unless the computer module is bad and just not reporting them, yikes).



With a bit of frustration I decided to take it on the road and push it as hard as possible to see what other symptoms I could detect or force out. I put it in first gear and began going fast, slow, up hills, down, flooring it, backing off, and manually shifting to other gears. I decided it wasn't a head gasket, leaking cylinder, or vacuum leak. These would be bad all the time. Not just when I moved the throttle a tiny bit. The transmission seemed to shift ok too as long as the throttle position was in the "sweet area". Loads up or down hills didn't seem to matter to the shifts in the good pedal area.



My pedal position still seemed the main factor. Running good, press a tiny bit more, running bad. So I'm down to fuel pump, ignition coils and computer module. At one time while in first gear, pedal to the floor, going up hill the engine light started flashing. "Good... more codes, more clues". This time it said cylinders # 1,3 and 4 were misfiring. Hmm, looking like possibly a weak fuel pump is starving the engine during heavy demand. Probably not the computer module as it seems to be reporting these things ok. The ignition coils remain on the list as well tough.



You have to drop the gas tank to replace the fuel pump. so I'm hoping that's not it. But based on the results, I'm resigned to the fact I'll probably be dropping the tank the following weekend. In the mean time I'm still thinking about the ignition coils. The v6 1MZ-FE has 3 of them. 2 spark plugs per coil. What are the chances that the coil for cylinders 3 and 4 might be bad? But then #1 reported a misfire too, what's with that?. And why would a coil seem fine, then act bad just because I moved the pedal just the tiniest bit? I've had coils on other cars go bad, but the car would always start rough and get worse as RPMs went up. Not the case here. Buying an unneeded coil can be expensive too, starting at $75 and going up fast. Well... I called and found a nearby auto store that had just one in stock for $70. The coils are easy to change so I thought, "what the heck, let's get a new one, swap one at a time and see what happens". If it doesn't help, maybe I can return for a refund on a new fuel pump later.



So, got the coil, replaced the one on plug 4 that also connects to 3 and fired it up. Since the problem only happens somewhere a little bit past half throttle I can't tell a difference yet until I can get out of the neighborhood and rev it up. Well you guessed it... the first time I gave it good throttle, it jumped. I slowed down and floored it... I was flying (well best you can in a mini-van anyway). Replacing the coil pack on 3/4 put me right back to full performance. I'm sure the new fuel filter helped too. I'm still leary that maybe the other 2 coil packs may be getting weaker since I got a code on #1 also. But things are running great now and I know if I notice similar symptoms, I'm dropping another coil pack or two.



Hope this helps someone and I didn't bore you too badly with my long post.



Plaz

Reply 1 : Fixed my 2000 Sienna, was running badly

I had the exact same symptoms and the exact same thing fixed it. I was terribly worried that it would cost me more than the vehicle was worth. I was so glad to have it be only one coil. I forget which one.

Reply 2 : Fixed my 2000 Sienna, was running badly

I too have a 2000 Toyota Sienna that exhibited very similar symptoms. Therefore I was very thankful to find this post!



I had gone through a similar path of diagnosis: bad fuel?-no; new spark plugs-a little better, but not fixed; new air filter-no; egr valve???; plug wires???. But that's when I found this thread and it all made sense.



I was getting error codes of P0300 (multiple or random misfire), P0301 (cylinder 1 misfire), P0304 (cylinder 4 misfire). And that's when I realized that on this year Sienna the coil actually controls two cylinders. Mine happened to be the coil over cylinder 4 that was bad, which also controls cylinder 1.



The cylinder order from left to right, back to front (starting with the cylinder closest to the passenger seat) is 1, 3, 5, 2, 4, 6. And the firing order is 1, 2, 3, 4, 5, 6. So, the coils are paired as follows: 5 & 2; 1 & 4; 3 & 6.



My van has 175,000 miles on it. Maybe others will experience this around this same age/mileage and will find this information helpful in getting their missing problems easily fixed!

Reply 3 : Fixed my 2000 Sienna, was running badly

First of all, thank you for posting this thread since I would not have, for the life of me, been able to narrow my similar situation to this potential issue. I live in California, home of the wonderful CARB and the ever evolving California emission policies. My car is currently being serviced by my mechanic and according to his code reader, it shows a misfiring at cylinder #6. Just last week it was a misfiring at cylinder #3. Prior to all this, I just had my catalytic converter replaced and all the spark plugs replaced with iridium units. Now I am currently experiencing a lack of power as I press the pedal closer to the floor. I also noticed an increase in rpms in order to accelerate. Before all this, I used to accelerate w/o hesitations, maxing an average around 3k to 3.5k rpms. Now, I float between 4k and close to 5k. Not to mention I seem to go through a tank of gas faster than usual. I will have to speak to my mech about a possible coil issue. I may look into replacing all coils just to eliminate the possibility. Man, this is getting expensive.

Reply 4 : Fixed my 2000 Sienna, was running badly

Davesgarage,



Cylinder 3 & 6 are driven off of one coil. And you can replace this yourself. There is one 10mm bolt holding it down and that's it! When you look in toward your engine it'll be the one on the right. It'll run you $70 or so from the car parts store.

Reply 5 : Fixed my 2000 Sienna, was running badly

At this moment, I still have some minor idling issues. I will start my own thread to detail my issue. Good luck to you, Plaz and thanks to those who responded.



Thursday, March 3, 2011



UPDATE: Problem has been solved! New coil purchased to replace the malfunctioning one. Van now flys! Wife took it for a spin and is now happy with it's acceleration.



Thanks TN and those whom helped!