2000 Avalon Drivability /Acceleration Issue

[nosretep]

After sitting for 6-8 hours, my 2000 Avalon with 177K will barely move when you press the accelerator. As the engine warms up, it improves enough to be driveable, but even when you're moving, if you try to slowly accelerate, there is limited response. If you push the accelerator to the floor, to try to get it to downshift, there is about a 3 second delay, then a jerk as the car accelerates, although at a slow rate.

I checked the spark plugs (great condition), replaced the fuel filter, then had a transmission guy drive the car because I thought maybe the tranny wasn't engaging. He's been repairing trannys for 25 years and said it's NOT the tranny, but would suspect either the fuel pump or a restricted exhaust system. I checked the fuel pressure (48 psi) and it jumps a bit when I blip the throttle, so I assume the pressure regulator is working, and when I shut the engine down the pressure only dropped a few psi in 10 minutes.

I hooked up my vacuum gauge and had only about 9" at idle. Removed the O2 sensor from the front bank (to allow more air to exit the engine in case the exhaust system was restricted) and vacuum rose to about 16". Reinstalled the O2 sensor and did some work to make sure the exhaust system has no restrictions. Now have 15" at idle, but periodically drops to about 10. If I blip the throttle, it will go back up to 15", but will drop again in about 30 seconds or so. Another blip raises it, etc. However, the vehicle still operates the same. TPS voltage increases linearly and within proper range while pressing throttle. MAF sensor ohms ok for the air temperature, and when advancing throttle the voltage for the air volume ranges from about 1.7 - 2.7 volts. My Chilton manual, in which I've already found mistakes (like claiming the fuel pump should operate when you turn the ignition key - it actually requires the crank to be rotating before the fuel pump in enabled) says the range should be .9 - 1.5 volts and to replace if out of range. This is a MAF from a salvage yard, which I installed last June, so I put the old one back in and it gave the same 1.7 - 2.7 volt range. When the engine is cold you wonder if the car will make it up a hill and it improves slightly as it warms up, but still the accelerator seems to have little effect.

I'm not sure whether 15" vacuum is an issue (should have checked that when the car was working well), but periodically dropping to 10" can't be good. Was thinking perhaps a flaky crank sensor could cause a problem with fuel delivery as the crank input is required for the fuel pump to operate, but everything I've read says a bad crank sensor will set a diagnostic code and I'm getting NO codes.

Any help would be greatly appreciated as I don't know what to do next (other than taking it to a shop and I've only done that once in the last decade when the clutch went on a FWD car in the middle of a MN winter, and I don't have a heated garage).

[wifelikesavalons]

The amount of vacuum at idle will be dependant upon your altitude. At 4500 feet typical idle vaccum on most cars is in the 15 to 17 in/Hg range. If your catalytic convertor was restricted, there is typically an underlying problem - most of the time it is a fuel control issue causing excess fuel in the catalyst causing it to melt and restrict. Look at the ari/fuel ratio sensor (some call it a front oxygen sensor even though it is an AFR sensor). If it is skewed and/or stuck it will cause improper fueling which can cause your concern.

[muddkatt]

On the girlfriends 2000 Avalon, she had a similar problem. I finally found out it was the MAF sensor. It was not defective, but rather coated with a film of oil. Cleaning it did the trick. It is now part of the regular maintenance.