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2001 Toyota Sienna Running Poorly in Cold Weather

I have a 2001 Toyota Sienna xle that started running rough when the weather turned cold. When started, the car idles very high and will not shift properly until it was been running for around 5 minutes. After that it will run well for about 10-15 minutes and then begin to run rough or poorly. The problem is very noticeable at low speeds and when stopped. It never actually kills, but it feels like it is going to. At high speeds it is less noticeable but occasionally you will feel it jerk or chug like the transmission is slipping or a belt or something.

I took it to a mechanic who checked the codes and found that the ignition coils were supposedly bad. I say supposedly because they replace three of the ignition coils and the problem still persists. I then took it back to the mechanic who then told me it was the oxygen sensor. The o2 sensor was replaced and the problem is still there with no noticeable improvement. I again to it back to the mechanic who tells me that they scratching their heads.

I have done some looking around on the internet and have found some discussions that seem to have some promising leeds and actually last weeks car talk show had a caller who described a similar problem. The guys told him it could be a oxygen sensor but they thought a better possibility would be EGR valve or a vacuum leak. Not sure if this sienna has an EGR, but I plan to suggest looking into it to the mechanic. Also, I found some discussions talking about the idle control valve and the engine control module.

Any help that can be provided will be greatly appreciated.

Also I am wondering how someone should deal with a situation like this. It was a tough decision to go ahead with the ignition coil replacement as this vehicle has over 280,000 miles and it cost $750. After that did not fix problem the mechanic didn’t charge me for the o2 sensor replacement. This seemed reasonable, but as that did not fix the problem either; I am left wondering how one should proceed. If they tell me they are unable to solve the problem; does that give me the right to a refund or at least a partial refund?

Thanks for your time and consideration.


It’s time for another mechanic.

Go to a Toyota dealer. Those guys have full access to all Toyota technical service bulletins, recalls, factory tools, training, etc.

I should think (hope) that somebody there is experienced enough to fix your problems.

I’d suspect the temp sensor. If the ECU doesn;t know the engine is cold, it’ll regulate the injector pulse wiidth based upon the “full temp” protocols and it’ll run terribly when cold. And, since the ECU has nothing to compare the temp sensor to, it doesn;t know it’s giving a false reading and won’t throw a code. If the ECU knew the engine was cold, it’d ignore the O2 inputs and feed more fuel in.

So have u fixed the toyota sienna problem?