hi, don't want to give up on my evo 4. it's a 98 lancer coupe with an evo 4 engine. tried almost everything and i couldnt find the reason for the rough idle. really hope someone from here could help.

 

maybe its the tune? have you tried getting it tuned.

my car used to have cold start issues and rough idle, i got it tuned and its fine now.

try doing a boost leak test aswell, maybe somewhere the car is leaking out vacume, that can cause rough idle aswell.

 

thanks for your reply. how do i go about with the tune? can the stock ecu of an e4 be tuned?

i already had it tested for vacuum leaks and still the rough idle exists. we swapped several parts as well just to check but to no avail.

swapped maf, throttlebody w/ servo, sparkplugs, plug wires and coil pack, fuel pump.

dont know what else to check.

 

Do you have a wideband gauge installed? Knowing your AFRs helps to see if you are running lean or rich. From there you can narrow your troubleshooting instead of just shooting in the dark. Would be even better if you can provide a datalog.

 

after all this, only tuning is left. give that a try aswell.

you need ecuflash and a flash cable to tune your car. you can get it done locally if there are people in your city who tune evo's or get email tuned from united states.

 

no I dont have one installed. but looking at my sparkplugs, i think am running lean. am planning to buy a obd 2 scanner

 

i also had a compression test. 170, 150, 160, 150.

 

firstly get a wideband and then go from there. see where your AFR's are and then proceed forward.

i dont think compression should have more that 15 diffrence, but im not sure.

im sure tuning will do the job because you did everything else, maybe a bump in timing or fuel will helpout.

 

It could be a million things. Without a way to datalog, you're kinda guessing. You can start checking and replacing things bit by bit, if you have no other options.

 

yes it should not go beyond 15 of a difference. so i have 2 cylinders that are too low.

damn cel wont turn on.

 

thanks. how do we get a datalog again?

 

first of all you get a tactrix cable and then you download evoscan software.

you connect your cable to your car's ecu and start datalogging.

its very simple but you need cable and software first.

 

Don't get hung up on the fact you have 2 cylinders are reading 15 psi lower than the others. Get a wideband and do some research on how to pull a datalog from your car. That will help point you in the right direction. Otherwise, like I said earlier, you'll be shooting in the dark. If you're not up to researching, have a competent mechanic take a look at it for you. We really can't do much here since a rough idle can be caused by lots of things.

 

i would suggest a afr gauge if you havent got one. then datalog, if nohting is showing you try the basics with maf and biss screw