Sluggish Acceleration, Timing Is Being Retarded

[RPrindl]

I have a problem with my 1994 Lexus ES300. It's been in my family since new in November 1993 and has 64,000 miles now. About 500 miles ago the engine light came on, the dealer replaced the rear O2 sensor and the light is off. But I notice that after the car is fully warmed up it has sluggish acceleration, and it's kind of intermittant. I hooked up an AutoTap OBD2 tool and saw the computer pulling out alot of timing when the problem occurs. It takes out so much timing that the exhaust manifolds glow red hot! That's why the Oxygen sensor died, the heater circuit failed due to all the heat. When the problem happens the timing goes from around 30 down to 5 degrees, which is basicaly pulling out ALL the timing down to the base timing set by the phyiscal position of the crank sensor.

The pseudo-OBD2 1994 diagnostics don't help much as they were just the first year and didn't really get perfected until 1996. Here is what I've done to the car:

New PCV valve

New Fuel Filter

New Air Filter

New Trans Filter and fluid

Changed Diff Fluid

New Platinum spark Plugs (factory spec)

Flushed Radiator (DexCool)

New Cam Belt (checked timing before & after OK)

Checked Valve Adjustment, all were within spec

Cleaned throttle body (was typical)

Cleaned inside Valve Covers and Intake Manifold while it was apart

New Sears DieHard GOLD battery & negative cables

Oil is spotless clean and was changed every 3000 miles.

Fresh tank of 93 octane gasoline.

I wanted to change all these parts anyway and was wishing it would solve the problem but it hasn't changed. I also did the following to eliminate some things:

New Coolant Temp Sensor (for Computer) only $30, was worth a shot.

Disconnected both Knock sensors, same sluggish acceleration problem, but OBD2 did see them disconnected so at least that works.

Cleaned cam and Crank sensors, measured resistance according to Factory Lexus Service Manual and is OK.

Measured resistance of Mass Airflow Sensor and is OK also acording to book.

Removed Cat Converter, it's honeycomb is in perfect condition, ran with test pipe to confirm.

I read that some guys on the Toyota Previa Yahoo Group have the EXACT SAME problem with their vans. This must be a common Toyota problem. They use the same part number MAF sensor as my car has.

Anybody have any information on this problem before I start replacing expensive parts??

Thank you

Roger

[Ronald]

It sounds like the engine is running lean, which would explain the retarded timing (knock sensor being zealous) and the hot exhaust (lean burn). A lean mixture increases the propensity of an engine to knock. Is there away to do a pyrometer test and measure the temperature of the exhaust gas and the catalytic converter?

This might cost some bucks, but I would have the other oxygen sensors and other feedback sensors checked. It's been awhile since I read the manual, but I think there is one in each exhaust manifold and maybe a fourth one somewhere else.

The problems sound like the lean burn issues of the pre-catalytic converter 1974 model cars with their built in retarded timing. Some people used to fiddle with their carburetors, illegally, by fitting richer idle and power jets to get around the hesitation upon acceleration. With the SFI these days, the correct stoichiometric mixture is not an issue, unless the feedback circuits have a problem.

I don't know how mixtures are checked these days, but I remember the carbureted Hondas used to have an inlet on the intake manifold for a propane tank attachment. If one added propane to the mixture and the idle cleared up and the exhaust temp was within specs, the mixture was judged to be too lean and adjustments were made.

[SKperformance]

you might be running rich from too much gas and not enough air. check to make sure there are no rips in the intake pipe or the maf being plugged makeing the engine think it is not getting as much air as it is.

[cui]

You probably have done this already....

Have you mesaured the injectors resistance? And took them out the see if they are not clogged?

I used to have car that has rust bits clogging the injector...it took me a long time to diag the problem as the injector resistence checks out okay....

[RPrindl]

If she was running rich or lean wouldn't it set a code?

I do wonder if a bad fuel injector could be causing the problem. I want to pull them out and have them cleaned & flow tested by a good shop like RC Engineering.

http://www.rceng.com/

New injectors are $100 each and cleaning is $25 each.

I have a winter beater Cavalier to drive so I can ship them out and wait. Has anyone here sent theirs out for cleaning?

My air intake tube is good, no cracks or rips. I did find a bunch of Oil in the tube from the PCV system which allowed the Oil vapors to backup into the tube between the throttlebody and airfilter. The vapors kind of turned into grease all over the place. The Mass Airflow Sensor (MAF) was full of oil. I replaced the PCV valve and grommet and it seems OK now. I'm also thinking of replacing the Mass Airflow Sensor part# 22250-20010 because I can't get all the oil out and wonder if it's causing my problem. A rebuilt A1 Cardone is $185.

I plan to put 100,000 more miles on this car so I don't mind spending money on it now inorder to make it care free in the future.

Thanks for the suggestions guys, I appreciate it!

[SKperformance]

No if it is a normal rich or lean condition it won;t give a cel.

If the maf is full of oil then you already know that is is the problem.

Take it to a pro and let them clean it ,as the filament inside is rather fragile but still should be able to be cleaned

[bartkat]

Yes, sure does sound like the MAF sensor. needs cleaned or replaced. I don't know about the 94, but most models will go into "limp" mode when the MAF isn't reading correctly.

[RPrindl]

We took the car to the Lexus dealer, Prestige Lexus in Ramsey NJ, and they charged us $450.63 to replace the Oxygen sensor and do their "55,000 mile service" (oil change & rotate tires). This was 500 miles ago.

The dealer fixed the problem, but NOT the cause of the problem. If continued driving the other Oxygen sensor would go bad also. (Both the front and rear exhaust manifolds glow red hot during agressive driving) The Lexus dealer missed the oil in the air intake tube and missed the bad PCV grommet seal during their 55,000 mile service. I got a new PCV valve and seal at Autozone for $10.

The dealer wanted us to do their "60,000 mile service" (spark plugs, coolant, brake trans & diff fluids, etc.) which was estimated at $880 plus tax, fluids, supplies, waste disposal fees, etc. This would be over $1000 by the time they were done. And that's without Cam belt or Valve adjustment. Their position on the car is "do those things first then we can look into the other problem" which I just can't afford to do.

I've had the MAF cleaned with a SafetyClean automotive parts cleaner, it uses mineral solvent. The dealer cost for this part is like $600.

Having been in situations like this with other cars I don't want to spend $3000 at the dealer to fix a $6000 dollar car. So far I'm out a little over $200 for the work I've done.

The search here on this forum hasn't given me any clear troubleshooting help. Perhaps this will help someone else in the future as I will post my findings when this is fixed.

Thanks for the suggestions guys, I appreciate it!

[cui]

You don't need to check valve clearance for 60k...I openned the valve cover and immediately know that there is almost impossible to wear down those shims...(unless the oil isn't lubricating.)

running hot is usually a indication of running rich...(the excessive fuel is the reasons for heats.)

btw, how do you check timing on the IMZ engine since there is no spark plug wires?

(this is exactly another reason why I don't like distributorless system....)

at this point of time, if I were you, I would also check for fuel pressure...and see if the fuel return line is not clogged or pinched.

[bartkat]

There are places online to buy those parts much cheaper than at the dealers. Often you can also get them at a Toyota dealer for about half of what Lexus charges.

[RPrindl]

The Lexus factory service manual calls for 60,000 miles or 72 months valve adjustment. The camshaft lobes are the part that wears down, causing an increase in clearance. I have a digital picture of a worn camshaft lobe but I don't have a place to host the picture.

The exhaust manifolds are running hot because the timing is grossly retarded therefore igniting the fuel mixture too late. This causes heat to be generated in the exhaust manifold rather than the combustion chamber. This excessive heat damaged the rear oxygen sensor. This will also burn the exhaust valve seats if not corrected.

All OBD2 cars run in a closed loop which adjusts the fuel inorder to maintain the proper air/fuel ratio. The service engine light isn't on, no codes are set, so it isn't running rich.

The ignition timing is easily checked by either using the service port on the motor and a timing light which triggers off the primary side of the ignition coil, as explained in the Lexus service manual. Or by using a laptop computer running OBD2 software and an interface cable that connects to the OBD2 port inside the fuse box. I chose the latter method.

If the fuel pressure were too high the closed loop OBD2 system would have to shorten the injector pulse width inorder to maintain the correct air/fuel ratio. This would cause the fuel trim numbers to go out of range and would set a code.

At this point I've given up on the Lexus dealer. I have a friend who works at an autoparts store and plan to get the MAF thru him. The injectors will be sent out to Marren fuel injection in CT for rebuilding. www.injector.com

Lucky for me the Lexus is a spare car and I don't have to drive it while I shop around for parts. After I get it running perfectly the mods can begin. he he

Thanks for the suggestions!

[bartkat]

Sounds like you got it handled.