Welcome Visitor! Please take a few seconds and JibbaJibba56
Well-Known Member
This is sort of a diagnostic step by step for rough idle on the 4 bangers (from personal experience with the 2.5L from 2000 2WD)...
I've read nearly every thread dealing with rough idle after I felt defeated that I couldn't smooth the idle out on my truck on my own and from a discussion on here, so here it goes.
1. If you have a CEL use that as the base for checking anytime something goes wrong. Autozone reads codes for free, generously, with a basic OBD reader that will give an idea of what zone or bank is at fault.
2. A typical print-out will list anywhere from 2-6 items that 'could' be at fault but by no means is exact just gives what the Engine control computer interpretation of what's wrong so don't panic and think its going to cost $2K to fix your $500 truck.
3. That being said, if you have a truck with a huge amount of miles on it (Say 150K or better) and you do not know the maintenance history, check your plugs first. Simple easy cheap fix and most likely they will need changed soon anyways. White, Brown, Crusty, Wet or any of the like says replace. You need that complete burn in the combustion cycle to maintain smooth idle and throttle response!
4. If plugs don't fix it or are un-needed, OR, you did not throw a CEL, start at the IAC valve. In my case it is located on the rear of the throttle body and looks like a soda can sticking out from no where (small shiny cylinder). Unplug that bad boy and see if any change occurs in the idle. If changed for the better, remove the IAC (literally two bolts) and clean it out using some carb cleaner. Make sure you let it fully dry and evacuate fumes from cleaner before reinstalling. If changed for the worse then move on IAC isn't whats bad. Don't forget to plug it back in!
5. Locate your Fuel Pressure Regulator (typically right on the fuel rail). There is a vacuum line that runs to it. Unplug the most convenient, safest end of the line to check operation. If idle begins to sputter worse, plug it back in ASAP. If no change, look to see if gas is making it into that line, if so you might want to find a new one.
6. While we are at the rail, I suggest getting a Fuel Pressure Gauge to check the rail pressure. 50-70 psi is nominal, any less tells you...
a.) Fuel filter super dirty or clogged
b.) Fuel pump on its last leg
c.) Extremely dirty injector (stuck open or leaking)
d.) Vacuum problem
The easiest of the above to check is a vacuum problem, simply grab some WD40 or carb cleaner and selectively spray vacuum lines/fittings one by one. If you have a leak and you spray it the engine will rev up a bit from the extra combustible fluid. FYI, the main vac is just under the injection rail on the 2000 2.5L so be sure to get some sprayed down there as carefully as possible (i.e. don't put your anything by moving parts). If you find a leak obviously repair it.
Next easiest would be the fuel filter, if you have the miles on the truck and you still have a stock one, just change it. It's cheap and easy and could actually solve the problem.
The fuel pump may be the more difficult to diagnose so and personally I still haven't found a sure fire way to be 100% on those other than it failing completely or by CEL
Injectors can be done relatively easily for a home garage mechanic. If you can change all 8 plugs on the 2.5 then you sure as heck can do the injectors. Remove that upper intake (take your time and be careful it only took me an hour to do so really don't rush it). Unbolt the fuel rail and disconnect the Fuel pressure regulator from the rail. Disconnect all of the injector harnesses and remove the entire rail assembly with the injectors. Be sure to spray WD40 or PB blaster around the injectors followed by shop air to blow away loose dirt before removing from engine though. Check the injectors for dirt, one of mine had a rather thick layer of nastiness on it. If this is your case then you can simply clean it. I work in a metallurgy lab and have access to an ultrasonic cleaner. I put all of mine in an ethyl-alcohol bath for 1 hour to clean the filter baskets and nozzle tips. Remember to remove the o-rings as to not damage them in the bath. Or just replace with new ones. Mine cleaned up and I put them in and they work really well. I know this because it was the last thing I did and the idle was restored to a very smooth purr.
7. Simpler things that can be checked are plug in sensors such as O2 and MAF. Unplug these one at a time to see if any changes occur, worse idle means move on, better idle may mean clean or replace.
This is by no means a comprehensive list but it is a list of 'common' issues with idle. It is likely that if you are experiencing rough idle with your engine that one or a combination of these will fix your woes. I personally have replaced the spark plugs, wires, an O2 sensor, cleaned injectors, cleaned the IAC and have replaced a few vacuum lines with a 53 piece mechanics set from craftsmen and a pair of welding pliers, an adjustable wrench, and a utility knife. If I total the time spent doing this stuff (counting removing and reinstalling the upper intake manifold 3 times) it takes only a weekend at most. If I tally my money spent, I come in at about $200 for plugs, wires, WD40, fuel filter,O2 sensor, and vacuum line. Really, you can fix this problem, just take your time and be methodical about diagnosing the issue.
Good Luck to all that have the rough idle, don't get discouraged, it can be fixed.
I've read nearly every thread dealing with rough idle after I felt defeated that I couldn't smooth the idle out on my truck on my own and from a discussion on here, so here it goes.
1. If you have a CEL use that as the base for checking anytime something goes wrong. Autozone reads codes for free, generously, with a basic OBD reader that will give an idea of what zone or bank is at fault.
2. A typical print-out will list anywhere from 2-6 items that 'could' be at fault but by no means is exact just gives what the Engine control computer interpretation of what's wrong so don't panic and think its going to cost $2K to fix your $500 truck.
3. That being said, if you have a truck with a huge amount of miles on it (Say 150K or better) and you do not know the maintenance history, check your plugs first. Simple easy cheap fix and most likely they will need changed soon anyways. White, Brown, Crusty, Wet or any of the like says replace. You need that complete burn in the combustion cycle to maintain smooth idle and throttle response!
4. If plugs don't fix it or are un-needed, OR, you did not throw a CEL, start at the IAC valve. In my case it is located on the rear of the throttle body and looks like a soda can sticking out from no where (small shiny cylinder). Unplug that bad boy and see if any change occurs in the idle. If changed for the better, remove the IAC (literally two bolts) and clean it out using some carb cleaner. Make sure you let it fully dry and evacuate fumes from cleaner before reinstalling. If changed for the worse then move on IAC isn't whats bad. Don't forget to plug it back in!
5. Locate your Fuel Pressure Regulator (typically right on the fuel rail). There is a vacuum line that runs to it. Unplug the most convenient, safest end of the line to check operation. If idle begins to sputter worse, plug it back in ASAP. If no change, look to see if gas is making it into that line, if so you might want to find a new one.
6. While we are at the rail, I suggest getting a Fuel Pressure Gauge to check the rail pressure. 50-70 psi is nominal, any less tells you...
a.) Fuel filter super dirty or clogged
b.) Fuel pump on its last leg
c.) Extremely dirty injector (stuck open or leaking)
d.) Vacuum problem
The easiest of the above to check is a vacuum problem, simply grab some WD40 or carb cleaner and selectively spray vacuum lines/fittings one by one. If you have a leak and you spray it the engine will rev up a bit from the extra combustible fluid. FYI, the main vac is just under the injection rail on the 2000 2.5L so be sure to get some sprayed down there as carefully as possible (i.e. don't put your anything by moving parts). If you find a leak obviously repair it.
Next easiest would be the fuel filter, if you have the miles on the truck and you still have a stock one, just change it. It's cheap and easy and could actually solve the problem.
The fuel pump may be the more difficult to diagnose so and personally I still haven't found a sure fire way to be 100% on those other than it failing completely or by CEL
Injectors can be done relatively easily for a home garage mechanic. If you can change all 8 plugs on the 2.5 then you sure as heck can do the injectors. Remove that upper intake (take your time and be careful it only took me an hour to do so really don't rush it). Unbolt the fuel rail and disconnect the Fuel pressure regulator from the rail. Disconnect all of the injector harnesses and remove the entire rail assembly with the injectors. Be sure to spray WD40 or PB blaster around the injectors followed by shop air to blow away loose dirt before removing from engine though. Check the injectors for dirt, one of mine had a rather thick layer of nastiness on it. If this is your case then you can simply clean it. I work in a metallurgy lab and have access to an ultrasonic cleaner. I put all of mine in an ethyl-alcohol bath for 1 hour to clean the filter baskets and nozzle tips. Remember to remove the o-rings as to not damage them in the bath. Or just replace with new ones. Mine cleaned up and I put them in and they work really well. I know this because it was the last thing I did and the idle was restored to a very smooth purr.
7. Simpler things that can be checked are plug in sensors such as O2 and MAF. Unplug these one at a time to see if any changes occur, worse idle means move on, better idle may mean clean or replace.
This is by no means a comprehensive list but it is a list of 'common' issues with idle. It is likely that if you are experiencing rough idle with your engine that one or a combination of these will fix your woes. I personally have replaced the spark plugs, wires, an O2 sensor, cleaned injectors, cleaned the IAC and have replaced a few vacuum lines with a 53 piece mechanics set from craftsmen and a pair of welding pliers, an adjustable wrench, and a utility knife. If I total the time spent doing this stuff (counting removing and reinstalling the upper intake manifold 3 times) it takes only a weekend at most. If I tally my money spent, I come in at about $200 for plugs, wires, WD40, fuel filter,O2 sensor, and vacuum line. Really, you can fix this problem, just take your time and be methodical about diagnosing the issue.
Good Luck to all that have the rough idle, don't get discouraged, it can be fixed.
Last edited:
