97 Camry Stumbling and hesitation fixed

[tbalon]

Hey guys, still strugling with a problem on my 1997 Camry 4cyl automatic and thought I would post to say what I have done to try to fix it.

I bought the car used about 4 months ago with 160K mi on it. The previous owner told me that he had replaced the radiator and recently done a tune up with plugs, wires and coils.

While the car would start and run ok, it seemed to lack power and torque and fuel mileage was down. It also had a CEL on and after pulling the code it was a P0401 EGR valve low flow. I tested the EGR valve by drawing a vacuum on it while the car was idling and it stalled the engine so I knew it was working. I did some more trouble shooting and found out the vacuum regulator had a bad diaphragm and so I replaced it. The CEL went a way soon after that. While this solved one problem it started another.

The car would now hesitate and stumble on take off after it was warmed up and would tend to misfire at and buck slightly at cruising speed (just as you lifted your foot off the gas to maintain your speed). If I disconnected the EGR valve it would run fine but still lacked power. I figured that if the engine was running rich it would exhibit many of these characteristics. Rich exhaust being recirculated back into the engine which was already running in a rich condition caused the misfire. I know that the EGR valve opens just off of idle and that seemed to be timed right with the stumbling. I also noticed that the exhaust pipe was very black as it would be in a rich condition. So I figured what tells the ECM when to run rich?... The temp sensor of course. The temperature gage seemed to be working fine and it showed the engine coming up to temp normally. I soon learned that there are two temp sensors on the engine... one for the gage and one for the computer (ECM). So I picked one up for the ECM at about $15 and replaced it. This seemed to make a little difference in performance. The hesitation and stumbling seemed to subside but after a cool down and restart, they are still there. Also on cold start the rpms only go to about 1100 at idle. After warm up it drops back down to around 750. Is that about right?

I learned much of what I needed to know about the engine and its performance right here on TN by reading through many of the great posts. Hopefully if anyone has any experience with this please let me know....

[Mister_Perkins]

Thanks for posting your Solution!

I'm sure this will help someone down the road

[redgtxdi]

Yes, thanks for the feedback!! That's important for us all. Crazy that a "temp sensor" would cause such havoc.

Care to tell us the specifics for where this sensor is??

Part #???

Anything to know about swapping it out??

Thanks in advance!!

[tbalon]

First I have to apologize for my original post. I thought I had it fixed by replacing the temp sensor for the ECM. Unfortunately the problem has returned. I have updated the original post to reflect that I am still working on trying to resolve the stumbling and hesitation issue. Any help would be greatly appreciated.

I would just like to restate that the issue of stumbling and hesitation goes away if I disconnect the vacuum line on the EGR valve and drive the car that way but of course if I do this for any length of time I am sure the CEL will come back on. Also I used an aftermarket vacuum modulator instead of a factory OEM, but I don't think that would affect it that much would it?

[tbalon]

I have tried to clean out the throttle body by using the spray cleaner. It did not change anything though. I removed the IAC actuator from the outside and checked to see if the valve rotated freely and it did. Does anyone know how to test that IAC valve? Thanks

[Mister_Perkins]

DIY removal & cleaning of IAC

[tbalon]

Thank you mister Perkins, I read the thread you referenced and it was very helpful. Today I am going to try a different vacuum modulator valve to see if it makes a difference.

[tbalon]

I ohmed the IAC and got readings of 21.1 and 21.0 respectively so it tested good. I also tried a different vacuum modulator that I picked up at the junk yard and it seems to be running much better! No more hesitation or stumble.... I still think it may be a bit down on power though and the timing belt makes a lot of noise like it is loose. I wonder if the timing belt being loose could alter the valve timing enough to make it loose power?

[Mister_Perkins]

definitely a loose timing belt can cause it to have low power. Especially if it skipped a tooth or two. I would put the engine at TDC and double check the timing!

[tbalon]

Thanks Mister Perkins. I will check the timing and let you know. I have tightened the belt once about a month back but it seems to have loosened again. Not sure why.... It appears to be in good shape and was changed when the car had about 130K mi as I was told, so the car now has 170K . The records indicate that the water pump and seals were replaced with the belt. The radiator was replaced a few months later so there might have been a time where it overheated although I am not sure on that. If it did overheat, would the timing belt be affected enough to cause it to become loose?

[Mister_Perkins]

Nahh .. usually the belt gets loose because of age and stretching. Toyota thought it was a good idea to use a manual tensioner instead of an automatic tensioner, so once you set it, instead of automatically getting the slack out it stays in the same spot. and lets the belt get looser and looser until it skips teeth. Luckily they made the engines non interference so you wont damage anything though. lol