Hey Guys.
I have a 98 Protege', 1.5L, auto, a/c..

Recently, my car has developed at idle issue. When I first start the car in the morning, it runs just fine. Idles perfectly. But once the car has warmed up, it starts acting up.
Once warmed, the car will either have a really rough idle or it won't idle at all.
I checked around under the hood for basic stuff like loose or bad vacuum hoses and unplugged sensors. All is well.
Checked the air hose from the MAF sensor to the throttle body. Its in great shape. No holes or cracks and still very flexible.
I did notice one thing that does have me concerned though. I hear a slight popping sound coming from the filter box coming down the line of course from the intake. Don't know if this would give any clue to what the issue is.
The check engine light has been on for over a year. I had it scanned numerous times and each time, the scanner says no codes to be found. Tried with several different scanners. Same thing. I disconnect the battery negative cable and turn on the headlight switch for a few min. Reconnect and the light is gone till I run the car for about 50 miles then it comes on again. Still no codes..

Anyone have any idea what to do with this?
Thanks

 

i don't know why there is no code coming up, maybe your module is faulty in a way that it does everything except delivering the codes to the scanner. You could try to have it re-flashed, if someone is willing to do this for cheap.

There is a code that seems to come up after about 50 miles or so: P0420, catalytic warm up efficiency....
That code is coming after the computer runs a test and finds a fault comparing the readings of the 2 O2 sensors. There are tons of possible reasons. You have covered some of them already. Next I would make sure that the EGR boost sensor can get the vacuum signal. The sensor sits on the firewall at the passenger side and there is a vacuum line going down and connects to a nipple at the back of the manifold. Pull it off and poke into the nipple with a strong wire. The wire should be about 3" long. I am sure you have to push it through some resistance. That resistance comes from carbon build up.
There are other cheap things you can do: clean the EGR valve by scraping out the canals. You have to take it off and you need a new gasket for about $5.00. With the trottle body off you can clean the EGR ports at the mouth of the manifold. Look at the 6:00 and 12:00 o'clock positions.
You can give the throttle body a good cleaning inside and out.
You can replace all vacuum lines for about $5.00.
You can look for vacuum leaks at the lower intake manifold gasket using an enrichment tool.
Disconnect and reconnect all electrical harnesses to ensure best possible contact.
Using the Haynes manual you can check all sensors and injectors for their voltages.
You can check the ignition by inspecting the spark plugs.
Pull a wire of one plug while the engine idles and see if it gets worse. If so that coil/wire/plug is likely alright. Do all four.
Inspect the distributor cap and rotor.
Check the injectors and fuel pressure.

If all that doesn't fix it you may have to replace the ECM so you can get the codes.

Good luck.

 

Thanks for the info Tan. I'll start the process tomorrow after work. (short day)

 

You are welcome.

And here is an additional thought: inspect the connectors for the scanner and check the connectors at the ECM. There could be a problem establishing contact, keeping the information from flowing to the scanner.

You can produce a code intentionally. I once disconnected the wire at the EGR boost sensor and immediately got the CEL with a code referring to the EGR Boost Sensor Circuit malfunction. This gives you a way to test after cleaning the contacts or replacing the ECM.

If a replacement ECM does not deliver codes to the scanner, the problem must be in the wiring harness.

 

Great Info.. Thanks!