I have an evo 4, i have an issue with the idle-ing, when it's suppose to idle it shakes and wants to go of, the rpm of the idle is there where is should be about 900, and doesnt move alot , just a lil, and i keep hearing from the muffler bup bup bup, like the car is not working correctly, but when i drive or when i rev it, it works great, i can hold it on for example 5k rpm without a problem, i also noticed my boost guage(bar) it indicates now vacuum 0.4 and keeps shacking to go to 0.3, it used to be 0.5 constant, what could be the issue? when i drive it also just picks its normal boost like it used to.. it just suddenly does this, started 2 days ago, before that it worked perfectly... no check engine light on or anything, looked for a boost/vacuum leak with soap water and then carb cleaner, didnt find anything, changed spark plugs, nothing, only thing i didnt change are the wires. i know the wires arent 100% because one of them broke of and i put it together and the car ran good after, also no check engine light on. and the fast idle works cuz when its cold the rpm is 1500 then when the engine is hot it goes to 900 but when the rpm is on 1500 it hardly fails , very little to nothing, any help ?

 

how is your cilinder head, valves guides and seals ???

 

Maybe the idle control valve going out? It's a little motor on the throttle body which modulates idle.

 

the cylinder head looks good and valves look good , didnt do compression test but, the valve cover seal maybe needs changing , i took out the sparkplugs yesterday and they were not wet, so that means its good, and i boost 0.9 bar and i dont notice any performance loss

 

i was thinking the idle control valve , but i ruled that out because the check engine light isnt on, and it actually stays on ~900 , its not all over the place, and the fastidle still works correctly

 

At a certain point the mechanical aspect of the throttle body will take over, and the valve no longer has affect on the throttle position.

I just replaced mine to resolve my idle problems, my idle would fluctuate and stall out every once in a while.

To check if this is the problem, you can pull out the idle control valve by removing three screws. While the valve is out have it plugged in, have someone turn the key to the on position, but do not start the car. You should see the valve move when the key is in the on position. If it does not push out consistently, or just spins freely it is time to replace.

There are two styles of these valves I have seen. The 03's have the older one, which has three plastic teeth that move the acutator back and forth which tend to wear out. My evo was an 04, which came with the redisigned part, but they also wear out.

 

ooooo i understand, my evo is an evo 4 , but could this problem be related to spark plug wire or a boost leak that still did not find?

 

Boost leak could also cause idle issues.

Also, my car never threw a code from all of my idle issues.

 

what were your exact symptoms?

i forgot to mention another symptom, when i reved it a bit a coupla times, it stopped failing for 2 min and started failing again, but that was a 1 time thing, when the fan is on it fails less also, and when im on the cold start when its on 1500 rpm, it hardly fails, just a tad

you know what the idle sounds like, like the engine has cams , but it doesn't

 

It's very weird mates, it does bup bup bup bup works good 2 sec, and does bup bup bup again ... and goes on and on in a loop... what could this be?

 

anyone?

 

bump?

 

bump?

 

pm me

 

What was the fix to this? My VIII just started the same thing a few days ago, after an intake/UICP upgrade. Boost leak tested it today and found a few small hose clamp leaks. There was a TINY one around that throttle body that I couldn't find though. Started the car, and still idles funky like the OP, and only at normal operating temp. Upon nosing around for the TB leak, the garage heater ran out of propane so I decided to call it a day. (26 degrees out.) However, I don't think this is the culprit. Any advice would be great, and thanks in advance.