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Several sensors later and nothing to show for it....

989 Views 5 Replies 4 Participants Last post by  fenixus
I am completely at my wits end hopefully someone will have a solution. My 99 Camry suddenly started hesitating when accelerating from stop and at highway speeds. Originally checked the spark plugs and switched them all out as I noticed that one was completely black however this had no effect. It was shooting a code of P0401 at which time I replaced the VSV, modulator and EGR valve. I know that the modulator was not working as it wasn't even moving the EGR when we replaced it. Once the modulator was replaced the EGR began to operate again and on test drive it appeared the problem went away until I drove approximately 10 miles and it started up again. Now the problem is still there however it is not as persitant as it was. Tried replacing the MAP sensor and that had no effect at all. The check engine light is currently not on and not blowing a code however this has been intermitant from the begining. I believe the vaccum lines are fine as I tested them and they have air flow without leaks. If anyone has any ideas I would greatly appreciate it. Thanks!:headbang:
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several sensors later

I am not into the mechanics of cars but I will share a very similar experience and hope it helps you. My car was showing the same code and the garage I went to cleaned and then changed the vacuum, valve... We actually went two rounds replacing parts that were just replaced. During that same time I was at a red light and my car would not accelerate when the light changed. It took several minutes until I could eventually move. I was told just recently that when the check engine indicator light is on it will sometimes cause this hesitation. I can't expalin it further, the Toyota dealership I dealt with had it looked over and said not to worry about it that once the engine code was corrected all was again well. I have not had any problems since. My Dad and brother did lubricate the area that allows for exceleration under the front hood.

As to the check engine, after the garage and then the Toyota dealer had several failed tries over a period of two years, an older mechanic remembered that he had heard that a reading can show up as putting out normal readings in the garage but not when actually driving on the road. They told me they tied the windshield wiper down to the window and had the hood up to do a drive. It has been a few years but I am thinking it might have had to do with the vacuum??? They changed so many things I just don't remember off hand. Maybe this will sound familiar to another who can pick up on what I am saying but it has to do with the output, it was showing normal in the garage but not on the road. It was fine after that.
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Well, Just got back from the dealer and I feel like an idiot but it was nothing more than a bad spark plug wire on cylinder 3. I don’t know why this wouldn’t have blown a code for misfiring or bad wire but the dealer said this caused a carbon buildup in the system from the cylinder 3 not firing hot enough. I installed all the old parts with the exception of the VSV because it was a nightmare to do and the vacuum modulator because it was clogged with carbon. I replaced all the autozone plug wires with dealer recommended NGKs from advanced and the car runs like a champ. Thanks for all the help and recommendations.
Sounds very strange, my friend. P0401 means Insufficient EGR flow.

If you had a bad spark plug wire on #3 cylinder, enough to cause a spark plug to look black compared to the rest, you should have had a code of P0303.

There is a disconnect here somewhere. No way your ECU would not have thrown a P0303 code if you had a bad #3 cylinder spark plug wire. Maybe you had 2 or more codes at the same time, but you only read the first one?
weird, i would swear i replied to this topic yesterday ...
... was there a same/similar one going recently (bad spark plug wire cyl #3) ? ...

glad the OP got it fixed though :thumbsup:
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