Erratic rough idle

[amacatan]

Hi all,

I have a 90 series 5VZFE Prado which erratically experiences rough idling (or misfiring). I have tried everything that may cause the problem as follows but still no luck:

- New spark plugs
- New spark plug wires
- New ignition coils (x3)
- New fuel filter
- New fuel pump

All parts used are OEM. I also had the injectors cleaned and all tested ok. I also poured two bottles of Toyota fuel injector cleaner as per the manufacturer's instructions.

Before experiencing the problem, I recently had the timing belt changed (as well as the tensioner bearings, water pump) and all of the belts (all OEM). All was running smoothly for about two months. The problem occurred after we went for a vacation from which we had not used the car for 5 weeks. The car would behave fine for 5 days then run rough for 2 days erratically.

Any suggestions/ideas?

 

[Rob Cowell]

Possibly a sticky EGR valve. That would tend to light your engine malfunction warning light though, although some ECU software waits for it to happen a few times before it lights up. A Techstream reader would tell you even if it wasn't worthy of a light.

 

[induna]

The first place to start with these motors is cleaning the MAF sensor. It can be easily removed, inspected, and cleaned with MAF Cleaner, which is a simple spray (only use MAF cleaner). It is located on the air intake just past the airbox, is attached by two screws, and has a five wire connector plugged into it. Simply disconnect the connector, remove the screws, thoroughly spray the silver wires with MAF cleaner (if these wires are not shinny silver, the MAF is definitely dirty). There is also another set of wires in one of the black plastic channels in the sensor which is not readily visible. This is the intake air temperature sensor. It should be sprayed as well. Once everything has dried completely, re-install the sensor and test.

The other thing you can do is pull the codes and see if there are are stored faults (You can find instructions for doing this on several forums.)

 

[amacatan]

The first place to start with these motors is cleaning the MAF sensor. It can be easily removed, inspected, and cleaned with MAF Cleaner, which is a simple spray (only use MAF cleaner). It is located on the air intake just past the airbox, is attached by two screws, and has a five wire connector plugged into it. Simply disconnect the connector, remove the screws, thoroughly spray the silver wires with MAF cleaner (if these wires are not shinny silver, the MAF is definitely dirty). There is also another set of wires in one of the black plastic channels in the sensor which is not readily visible. This is the intake air temperature sensor. It should be sprayed as well. Once everything has dried completely, re-install the sensor and test.

The other thing you can do is pull the codes and see if there are are stored faults (You can find instructions for doing this on several forums.)

Thanks induna! I have cleaned the MAF sensor with no positive results. Could you post pics on where the intake air temperature sensor is?

There are no codes returned when I had it checked using obd ii.

 

[Shayne]

I don't know this engine at all but i think the clue is in the pattern "fine for 5 days then rough for 2" I bet the truck has a day off in between ?

If that's the case there is probably a pin hole in the fuel lines somewhere that is sucking air in . No codes for running out of petrol i don't think .

 

[StarCruiser]

Try and see what the weather is when it's running rough. It could be a poor connection with some corrosion. I would suggest checking every connector for correct fit and intact seals as well as for any sign of corrosion or dampness.

The other thing that is worth checking is that the air intake between the maf sensor and the intake manifold is not split.

 

[induna]

Thanks induna! I have cleaned the MAF sensor with no positive results. Could you post pics on where the intake air temperature sensor is?

There are no codes returned when I had it checked using obd ii.

I don't have a photo, but on the MAF sensor you immediately see the two wires for the MAF portion sitting in the large plastic archway when you remove it. Towards the base of the sensor there is an additional plastic hollow and the temp. sensor wires are buried in there. Simply sphray the hollow well with the MAF cleaner. You also might want to try posting on the Australian site Pradopoint since there are a lot more gasoline engine 90 owners there.

My 2001 90 is not ODBC II -- it is a european model that was sold in Central America -- and the codes have to be pulled by shorting two terminals on the test port under the hood and counting the blinks on the check engine light. Yours sounds different.

Good luck.

 

[amacatan]

Is it possible to have an injector that is bad and not have a check engine light?

 

[induna]

Another possibility is that the MAF sensor is bad. Apparently they can fail without necessarily throwing a code. The test for this is quite simple according to several posts I've read. Simply disconnect the MAF sensor and start the engine. This will definitely throw a code and will put the engine into limp-home mode. However, if the MAF is bad, the engine should idle smoothly and run well up to the 3000 RPM limp-home limit while it is disconnected. I have not tried this myself.

The reason I keep mentioning the MAF is because dirty/failed MAFs are notorious for causing intermittent poor idle, lrough-running, ow-power, high fuel usage, etc. without lighting the check engine light.

 

[alfa]

danke

 

[Umar]

If the misfire or rough idle is only at idle speed I would also make sure the idle control valve is clean and functioning correctly if the roughness continues at higher revs then I doubt it's the idle control valve. Does it misfire at all temperatures?