rough idle

[4Runninfun]

Truck is almost ready to go just have two things left, first hook up a couple gauges second figure out why my idle is acting up. when i first start the truck up from cold it will idle fine for about 5-10 seconds then it starts sputtering and will die out. as it gets warm it does a bit better but is still not great. i replaced the coolant temperature sensor and that seamed to help a little bit. any other thoughts on the matter?

[Funrover]

Is it your brake vacuum again?

[Brody]

My first two thoughts are the MAF sensor and/or the O2 sensor. I would take some MAF cleaner to it and also take out and clean off the O2 sensors using the same MAF cleaner.

'They' say that you can't or aren't supposed to clean the O2 sensors, but I never have had any trouble. They gum up much like spark plugs and everyone knows that you can clean them off. I have been reluctant to use carb cleaner on the O2 sensors, but the MAF cleaner seems to work just fine. I have cleaned mine out twice since I have owned the truck (7 years) and there never seems to be a problem. I will probably do it again soon, too.

Hope this helps. Whenever stuff like this happens with an EFI it always seems to be electrical related and usually something that sends a signal to the ECU is the culprit.

[Funrover]

My first two thoughts are the MAF sensor and/or the O2 sensor. I would take some MAF cleaner to it and also take out and clean off the O2 sensors using the same MAF cleaner.

'They' say that you can't or aren't supposed to clean the O2 sensors, but I never have had any trouble. They gum up much like spark plugs and everyone knows that you can clean them off. I have been reluctant to use carb cleaner on the O2 sensors, but the MAF cleaner seems to work just fine. I have cleaned mine out twice since I have owned the truck (7 years) and there never seems to be a problem. I will probably do it again soon, too.

Hope this helps. Whenever stuff like this happens with an EFI it always seems to be electrical related and usually something that sends a signal to the ECU is the culprit.

I have also used electrical parts cleaner and been ok! :thunb:

[4Runninfun]

it shouldn't be the MAF since that has not changed between the motor swaps, but the o2 sensor has, i'll put in the old (actually almost brand new) sensor and see if that helps. I figure it SHOULD be something that changed between the two motors.

[Brody]

Since you mentioned that, if there is big difference in the years between the two engines and/or if you swapped the ECU, you may need to double check to see if that particular motor had two O2 sensors on it. Maybe not, but they did do that on the V6 engines..It will run, but not quite right and the ECU will be trying to sort out all sorts of mixed signals.

It may also be worthwhile to pop out the hard to get to EFI relay--the silly one that you have to take the fuse box off to loosen(:eek:) and put it back in after you change the sensor. This supposedly resets the ECU and also will get rid of the 'check engine' light. There is also a specific amount of time you need to have this out. I don't know exactly what it is, but 10 minutes does the trick.

[transplant87]

im havin the same problem with my moms explorer wat do u think i should do. it runs really bad at start and it rev's up by itself but when it warm up it runs fine all day.

[Brody]

What year?

I know Jon has just redone his engine so I didn't mention the throttle body or cleaning it, but if stuff hasn't been done for awhile, I would start with that. Then do the MAF sensor clean out. A lot of people don't like using the MAF cleaner, but I have never had any problems with it. It needs to be specifically MAF cleaner, too as anything else will jack the truck up.

There are a couple of wires inside the MAF that read stuff like air flow and temperature and send the signal to the ECU. These get gummed up and send false signals so that the car gets too much or too little air or fuel.

I am no expert, nor even a for real mechanic, but the EFI stuff has a lot of sensors that send signals to the ECU and it is really easy for them to get crudded up just enough to start jacking with the engine. I am simply saying that this is where I would start....mainly because it is cheap and fast. Then if that doesn't work, you have at least eliminated those as problems and it doesn't hurt a bit to do it anyway...

[transplant87]

its a 98. i put my scaner on it and it sayin its the idel air controll so we replaced that and its sstill messed up:mad:

[porkchop]

i had inconsistent idle problems due to a gunked up fuel filter if you have an easily replaceable fuel filter you should change that just to be sure should be an easy cheap fix if it works if not then you know its taken care of and its not the problem.