2000 Corolla P0171, P0304, very sluggish (long post)

[eclecticmn]

I have continued problems with very sluggish acceleration with my 2000 Corolla CE, having 120,000 miles. I have more time than money right now so I tried to fix it myself, thinking that this would be simple, maybe plugs or whatever. Right now it is difficult to even climb a hill unless my engine has been running for some time. I will throw in some added content below to help anyone else having my problems who is as clueless as I am.

I have to spray starter fluid in the air intake filter to get it to start some times. eventually it runs great on the highway.

0. The OBDII thing read P0304 and P0300 and P0171, meaning misfire on 4, general misfire, and lean mixture. Sometimes also P0303.

1. I replaced the spark plugs with new approved plugs. The 4 plugs are under the easily removable engine cover in 4 deep wells under the 4 coil pads which look llike 4 plastic square pieces. There are no spark plug wires.

2. I inspected the fuel pump by removing it from under the rear seat. The plastic fuel pump assembly is maybe 6 inches in diameter and 8 inches tall. Inside is the fuel pump which is metallic and twice the size of a shotgun shell. The fuel filter looks like a horseshoe from the top, and is the size of a small hand curled around the fuel pump viewed from the side. There is an external strainer sock as well. I blew air through the fuel filter and some dirty spray came out.

Note: If you buy a fuel pump from NAPA/whoever, you only get the fuel pump, not the assembly, and not the fuel filter. I did find a separate fuel filter on the Internet, but it was hard to find.

3. I later tested the fuel pressure and it was OK. Maybe 27 as I recall. The fuel pump relay is directly behind the pivoting change compartment near the driver's left knee. It is on the lower left when looking toward the drivers side quarter panel from under the dash board.

4. A shade tree mechanic looked at it, and suspected a vacuum leak, but could not find one, but did not test the vacuum. He replaced the air intake manifold at my request and manually cleaned out the throttle body assembly very well. He swapped around the coil pads but the misfire problems stayed with cyliner 4, sometimes also 3. I had cleaned the mass flow sensor with approved stuff.

He suggested using lots of Sea Foam and some Marvel mystery oil.
The Sea Foam seems to have helped and it ran better, but I suspect I was treating the sympton, not the cause.

5. I replaced the oxygen sensor that is upstream of the catalytic converter. This was hellish until I learned to lean over the engine from the passenger side and use my LEFT hand.

Also, put in new EGR and PCV valve.

It is now as bad as ever.

What to do? I would like to fix it myself rather than admit to failure, wasting money, and being a moron.

Will a Toyota dealer plug in some superdiagnostic and find the problem in no time? How much would this cost to diagnose?

P.S. I really hate the Haynes manual for this car and year.

[randini667]

I had similar issues with mine, so I would recommend doing a compression test next.

-Rand

[eclecticmn]

I was reading other posts on this forum and noticed something unusual. One suggestion for a similar problem was an exhaust gasket leak upstream of the first O2 sensor.

In the past I have noticed a loud exhaust noise at times, as though I had a hole in a muffler, except it seemed to come from the front of the car. It is intermittent, and may happen more when it is foggy. A mechanic looked for it 6 months ago when he had the car up on the rack but could not find anything.

I wonder if these two are connected?

Also, where do I check for vacuum on a 2000 Corolla? I have a vacuum gauge but no clue.

[Crowbar911]

The P0171 can also indicate a dirty MAF, causing the car to run lean and possibly a misfire?


I replaced the MAF, and the code went away when I had it.

[genti]

eclecticmn, I am in the same boat and if you are still checking this I would love to find out what you did.
I have the same noise from the front of the car, somewhere in around the bottom.
It definitely is loud when you hit water on the road and that is maybe why you say you hear it more when is foggy. Or maybe because there is less wind and the sound bounces.

[dimwittedmoose51]

I'm thinking either exhaust leak or vacuum leak and here's why:

You say the motor doesn't run well until it's warmed up. That could be a coolant temperature sensor that's not reading properly. It's test is in the Haynes manual. If it's bad, make sure you buy one made in Japan or the US, not China. I found a Mintex(Japan) on ebay for like $30. The other possibility is clogged fuel injectors, but doing the SeaFoam through the brake vacuum hose doesn't seem to have solved your problem.

Fast Forward to the leak. When the motor is cold, ANY exhaust leak or vacuum leak will show up big time with crappy running. As the motor warms up, it's possible that the metal/rubber parts warm and expand enough to mostly seal whatever leak you have when the motor is cold, so diagnosing the leak will have to be done when the engine is first warming up. One friend of mine suggests using an incense stick if you have access to indoor service or a non-windy day outside. Light the stick and see if the smoke moves towards a certain area of the engine as you move from suspect joint/hose to suspect joint/hose.


Exhaust leak is harder to diagnose for me anyway. I have used an assistant at the rear tail pipe with the engine running and had them use an old t shirt or other wad of cloth and temporarily plug the tailpipe. The engine should die pretty quickly when this happens and if it doesn't, then from under the car,you should be able to tell where the exhaust is escaping to keep the motor running by hearing the hissing of the exhaust noise that wasn't there before the plug was activated. Make sure your assistant has work gloves on to protect their hands from heat.

Good luck with the search

DM&FS

[genti]

I found an exhaust leak and it is running better although I am not sure because of the ECU reset or simply the improved exhaust(I am not 100% sure yet that the leak has been sealed). Look for the down pipe exhaust gasket, also called, doughnut, or engine bottom. Google Exhaust Spring Bolt Kit (Bosal). There is also another gasket that connects the pre-cat pipe, right under that clamp before the converter, get them both.