intermintant check engine

A few weeks back the 97 2.4 acted like a miss then the check engine light popped on. Noticed reduced power but then the light went off and back to normal. Checked for codes and none reported.
Don't drive it much, so just swapped plugs wires and cleaned the intake and PVC system along with replacing suspect vacuum lines. Was off for a little while 10 -15 miles and now its back to the point it runs really rich and almost stalls when the light comes on. A random issue , searched the web and haven't found anything that points to something .

Thanks

 

If you dont have a code reader a local auto parts store should be able to scan if for you. Dont buy any parts recommended as a result of their code reading. While you had the hood open did you see any signs of a rat or mouse... little poop dropings all over the place? They love to chew on wires on vehicles that sit for extended periods. Get back to us with the code(s).

 

LOL... spot on Glamisman, those little guys do like to eat our wires, the rascals, if given the chance.
Thanks to the "Green" revolution our wires are often insulated with soy based instead of petroleum sheathing.
What great ideas are next?

 

you just have to look at anything FCA puts out for what not to do. There are people with 08/09 ish Challengers that have to scrape the car because the main harness is no good and there arent any replacement harness's avalible.

 

The check engine light comes on when the engine runs rough and rich but does not store a fault code. I have even tried to see if anything is logged while the event is on going and nothing. Starting to swap out the usual suspects hoping to find the elusive sensor or valve. The truck is over 20 years old really hasn't had any issue until now so its pretty much all original minus the standard tune-up stuff.

 

Is the CEL solid or blinking? Blinking would indicate a misfire. Solid would be something else.

 

this is going to be tough, very tough without a direction to go. Does your scan tool have the capability to see pending codes? Pending codes are codes that are stored in memory but have not meet the critiria for setting a check engine light. The flashing of the CEL is telling you stop... eminant engine damage.

 

rats have been eating wires sine well before the "green" revolution. Something my grandfather (born in 1903) often complained about.

 

the Light stays on when the engine is running rough but when it seems to run better the light goes off. I have a used multiple scanners to rule out any issues with that and no faults showing or pending. If something would fail it would be easier. Oh well starting with the TPS and working my way around.

 

Sounds like the computer is going into fail-safe mode back-up function because in this situation the code may not be stored.. The repair manual says:

HINT: If the engine is controlled by the back-up function, the MIL lights up to warn the driver of the malfunction but the DTC is not output.

Some of the problems that will trigger a fail-safe mode won't make the engine run too bad. For example with a bad intake air or coolant temperature sensor the computer just assumes a fixed temperature.

What will cause a worse running condition is a problem with the mass air flow sensor. In this case the computer fixes the ignition timing at 5 degrees BTDC and fixes the fuel injector pulses. Check for leaks in the intake after the mass air flow sensor and check the sensor itself as well as the o-ring/gasket around it.

Throttle position sensor would probably be the second thing to check.

 

So after more trail and error and nothing making any sense. I took it to Toyota figured they might have some experience to find what's up after $ 300 of advanced diagnostics they recommended swapping out all electronics starting with sensors. A total waste they really just Googled and had no clue. So I started testing each sensor until I came to the ECU opened it up and found a popped capacitor... Now the fear is what made that happen but after talking several repair sites its rather common. Of course Toyota used several ECUs that year making finding the exact one real hard but for only $500.... I was able to replace it and its back to normal.
So thanks for the support here !

 

Glad it's working now.

Why didn't you just replace the capacitor for $1? You could still do it and have a backup or sell it.

 

The Cap was only 6 cents and I was ecstatic to find it and be so cheap but after looking at the board under a magnifier the damage was more extensive. Repairable maybe but probably not reliable.

 

Awesome work man! That's great to hear!

 

The fact it ran at all is pretty amazing !!

Glad you figured it out .

A shame the Toyota Techs could not figure the problem .

Then your truck being so old might have been older then them if it did not tell them the problem completely clueless