Diagnostic Codes 25 and 26

[palos]

The car is an '88 Supercharged MR2. Yesterday, without prior warning or symptoms, it was difficult to accelerate from a standing stop or accelerate at slower speeds. Once the car began accelerating, it would do just fine. The clutch is not slipping, but I need to rev the engine to actually get the car moving. It just seems like its bogging down.

I checked the diagnostic codes this morning. Codes 25 and 26 were flashed -- essentially air/fuel mixture is too lean (Code 25) and air/fuel mixture is too rich (Code 26). I have the BGB, both the e-version and more coveted paperback edition, which doesn't really narrow down the possible source of the problem all that much, (i.e. fuel pressure, ignition, O2 sensor, ECU, AFM, air leaks). I also noticed an annoying whining sound, which I am presuming is one the pulleys or belts.

The O2 sensor, cap, rotor and plugs were replaced earlier in the spring, but I will check them nonetheless. Next I was going to check the timing belt and ignition timing. Then loosen or remove the alternator/AC belt and the water pump/supercharger belt to isolate the pulley or belt causing the whining. Also, I'll check the tension on the timing belt.

When I had the car idling today, checking for air leaks, it seemed to be idling rough. At times I could give it half throttle and nothing happened, i.e. engine revs did not increase; other times the revs would slowly increase; and then another time the engine revs increased immediately. The BGB isn't referencing the throttle positioning sensor (FI-26 and FI-62), but it almost seems as though it should come under scrutiny.

I'm also thinking of disconnecting the O2 sensor to see whether it puts the ECU into limp home mode, but makes the throttle more responsive. (Sounds oxymoronic, but limp home mode may be an improvement.)

Any other suggestions? Or perhaps you have experienced the symptoms and arrived at a solution.

Thanks in advance.

[dirocyn]

Both rich and lean? That's got vacuum leak written all over it. Most probably, varying amounts of unmetered air are getting into your system. Usually vac leaks hiss or whistle, could that be your "whine?"

Do a quick visual inspection, follow all vac hoses from one end to the other. You'll probably find something's come loose. If that doesn't find it, a mechanic's stethoscope (a couple feet of rubber hose) can often help you pinpoint sounds. Or use a propane torch (unlit), when you get it near a vac leak the engine will change how it's running.

[palos]

dirocyn: Thanks for the suggestion -- usually I spray throttle body cleaner and listen for the idle to increase.

My neighbor suggested the EGR and AFM, essentially inspecting and cleaning. So I'll include those into the fray as well.

[mr2tim]

Your book refers to the checklist on page Fl-46 why not run down that list?

[palos]

Actually, page FI-46 appears to be identical to page FI-62 I referenced above. FI-46 is in the 4AGE section of the BGB and FI-62 is in the 4AGZE section.

[palos]

I choose to run my car without the timing belt covers and the belt must have jumped a tooth at the crank. When the crank was at TDC, both the cam gears were one tooth off (counterclockwise). After inspecting the belt, the timing was corrected and the car is running like it did just a few days ago.

[With the Cusco crank pulley, I loosened the water pump belt and then removed its pulley to gain additional clearance. To loosen the timing belt adjuster pulley bolt, I had to grind a 10mm box end wrench to make it thin enough to fit between the crank pulley and the twelve-sided 10mm bolt.]